Adding upstream version 15.5.upstream/15.5

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
author: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-05-04 12:17:33 +0000
committer: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-05-04 12:17:33 +0000
commit: 5e45211a64149b3c659b90ff2de6fa982a5a93ed (patch)
tree: 739caf8c461053357daa9f162bef34516c7bf452 /doc/src/sgml/html/glossary.html
parent: Initial commit. (diff)
download: postgresql-15-5e45211a64149b3c659b90ff2de6fa982a5a93ed.tar.xz
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+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Appendix M. Glossary</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="acronyms.html" title="Appendix L. Acronyms" /><link rel="next" href="color.html" title="Appendix N. Color Support" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">Appendix M. Glossary</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="acronyms.html" title="Appendix L. Acronyms">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="appendixes.html" title="Part VIII. Appendixes">Up</a></td><th width="60%" align="center">Part VIII. Appendixes</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="color.html" title="Appendix N. Color Support">Next</a></td></tr></table><hr /></div><div class="appendix" id="GLOSSARY"><div class="titlepage"><div><div><h2 class="title">Appendix M. Glossary</h2></div></div></div><p>
+  This is a list of terms and their meaning in the context of
+  <span class="productname">PostgreSQL</span> and relational database
+  systems in general.
+ </p><div class="glosslist"><dl><dt id="GLOSSARY-ACID"><span class="glossterm">ACID</span></dt><dd class="glossdef"><p>
+     <a class="glossterm" href="glossary.html#GLOSSARY-ATOMICITY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ATOMICITY" title="Atomicity">Atomicity</a></em></a>,
+     <a class="glossterm" href="glossary.html#GLOSSARY-CONSISTENCY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CONSISTENCY" title="Consistency">Consistency</a></em></a>,
+     <a class="glossterm" href="glossary.html#GLOSSARY-ISOLATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ISOLATION" title="Isolation">Isolation</a></em></a>, and
+     <a class="glossterm" href="glossary.html#GLOSSARY-DURABILITY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DURABILITY" title="Durability">Durability</a></em></a>.
+     This set of properties of database transactions is intended to
+     guarantee validity in concurrent operation and even in event of
+     errors, power failures, etc.
+    </p></dd><dt id="GLOSSARY-AGGREGATE"><span class="glossterm">Aggregate function (routine)</span></dt><dd class="glossdef"><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION" title="Function (routine)">function</a></em></a> that
+     combines (<em class="firstterm">aggregates</em>) multiple input values,
+     for example by counting, averaging or adding,
+     yielding a single output value.
+    </p><p>
+     For more information, see
+     <a class="xref" href="functions-aggregate.html" title="9.21. Aggregate Functions">Section 9.21</a>.
+    </p><p>See Also <a class="glossseealso" href="glossary.html#GLOSSARY-WINDOW-FUNCTION">Window function (routine)</a>.</p></dd><dt><span class="glossterm">Analytic function</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-WINDOW-FUNCTION">Window function (routine)</a>.</p></dd><dt id="GLOSSARY-ANALYZE"><span class="glossterm">Analyze (operation)</span></dt><dd class="glossdef"><p>
+     The act of collecting statistics from data in
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">tables</a></em></a>
+     and other <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relations</a></em></a>
+     to help the <a class="glossterm" href="glossary.html#GLOSSARY-PLANNER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-PLANNER" title="Query planner">query planner</a></em></a>
+     to make decisions about how to execute
+     <a class="glossterm" href="glossary.html#GLOSSARY-QUERY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-QUERY" title="Query">queries</a></em></a>.
+    </p><p>
+     (Don't confuse this term with the <code class="literal">ANALYZE</code> option
+     to the <a class="xref" href="sql-explain.html" title="EXPLAIN"><span class="refentrytitle">EXPLAIN</span></a> command.)
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-analyze.html" title="ANALYZE"><span class="refentrytitle">ANALYZE</span></a>.
+    </p></dd><dt id="GLOSSARY-ATOMIC"><span class="glossterm">Atomic</span></dt><dd class="glossdef"><p>
+     In reference to a <a class="glossterm" href="glossary.html#GLOSSARY-DATUM"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATUM" title="Datum">datum</a></em></a>:
+     the fact that its value cannot be broken down into smaller
+     components.
+    </p></dd><dd class="glossdef"><p>
+     In reference to a
+     <a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION" title="Transaction">database transaction</a></em></a>:
+     see <a class="glossterm" href="glossary.html#GLOSSARY-ATOMICITY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ATOMICITY" title="Atomicity">atomicity</a></em></a>.
+    </p></dd><dt id="GLOSSARY-ATOMICITY"><span class="glossterm">Atomicity</span></dt><dd class="glossdef"><p>
+     The property of a <a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION" title="Transaction">transaction</a></em></a>
+     that either all its operations complete as a single unit or none do.
+     In addition, if a system failure occurs during the execution of a
+     transaction, no partial results are visible after recovery.
+     This is one of the <acronym class="acronym">ACID</acronym> properties.
+    </p></dd><dt id="GLOSSARY-ATTRIBUTE"><span class="glossterm">Attribute</span></dt><dd class="glossdef"><p>
+     An element with a certain name and data type found within a
+     <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">tuple</a></em></a>.
+    </p></dd><dt id="GLOSSARY-AUTOVACUUM"><span class="glossterm">Autovacuum (process)</span></dt><dd class="glossdef"><p>
+     A set of background processes that routinely perform
+     <a class="glossterm" href="glossary.html#GLOSSARY-VACUUM"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-VACUUM" title="Vacuum">vacuum</a></em></a>
+     and <a class="glossterm" href="glossary.html#GLOSSARY-ANALYZE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ANALYZE" title="Analyze (operation)">analyze</a></em></a> operations.
+     The <a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC" title="Auxiliary process">auxiliary process</a></em></a>
+     that coordinates the work and is always present (unless autovacuum
+     is disabled) is known as the <em class="firstterm">autovacuum launcher</em>,
+     and the processes that carry out the tasks are known as the
+     <em class="firstterm">autovacuum workers</em>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="routine-vacuuming.html#AUTOVACUUM" title="25.1.6. The Autovacuum Daemon">Section 25.1.6</a>.
+    </p></dd><dt id="GLOSSARY-AUXILIARY-PROC"><span class="glossterm">Auxiliary process</span></dt><dd class="glossdef"><p>
+     A process within an <a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE" title="Instance">instance</a></em></a>
+     that is in charge of some specific background task for the instance.
+     The auxiliary processes consist of 
+     
+     the <a class="glossterm" href="glossary.html#GLOSSARY-AUTOVACUUM"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AUTOVACUUM" title="Autovacuum (process)">autovacuum launcher</a></em></a>
+     (but not the autovacuum workers),
+     the <a class="glossterm" href="glossary.html#GLOSSARY-BACKGROUND-WRITER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-BACKGROUND-WRITER" title="Background writer (process)">background writer</a></em></a>,
+     the <a class="glossterm" href="glossary.html#GLOSSARY-CHECKPOINTER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CHECKPOINTER" title="Checkpointer (process)">checkpointer</a></em></a>,
+     the <a class="glossterm" href="glossary.html#GLOSSARY-LOGGER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-LOGGER" title="Logger (process)">logger</a></em></a>,
+     the <a class="glossterm" href="glossary.html#GLOSSARY-STARTUP-PROCESS"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-STARTUP-PROCESS" title="Startup process">startup process</a></em></a>,
+     the <a class="glossterm" href="glossary.html#GLOSSARY-WAL-ARCHIVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-ARCHIVER" title="WAL archiver (process)">WAL archiver</a></em></a>,
+     the <a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECEIVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECEIVER" title="WAL receiver (process)">WAL receiver</a></em></a>
+     (but not the <a class="glossterm" href="glossary.html#GLOSSARY-WAL-SENDER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-SENDER" title="WAL sender (process)">WAL senders</a></em></a>),
+     and the <a class="glossterm" href="glossary.html#GLOSSARY-WAL-WRITER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-WRITER" title="WAL writer (process)">WAL writer</a></em></a>.
+    </p></dd><dt id="GLOSSARY-BACKEND"><span class="glossterm">Backend (process)</span></dt><dd class="glossdef"><p>
+     Process of an <a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE" title="Instance">instance</a></em></a>
+     which acts on behalf of a <a class="glossterm" href="glossary.html#GLOSSARY-SESSION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SESSION" title="Session">client session</a></em></a>
+     and handles its requests.
+    </p><p>
+     (Don't confuse this term with the similar terms
+     <a class="glossterm" href="glossary.html#GLOSSARY-BACKGROUND-WORKER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-BACKGROUND-WORKER" title="Background worker (process)">Background Worker</a></em></a> or
+     <a class="glossterm" href="glossary.html#GLOSSARY-BACKGROUND-WRITER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-BACKGROUND-WRITER" title="Background writer (process)">Background Writer</a></em></a>).
+    </p></dd><dt id="GLOSSARY-BACKGROUND-WORKER"><span class="glossterm">Background worker (process)</span></dt><dd class="glossdef"><p>
+     Process within an <a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE" title="Instance">instance</a></em></a>,
+     which runs system- or user-supplied code.
+     Serves as infrastructure for several features in
+     <span class="productname">PostgreSQL</span>, such as
+     <a class="glossterm" href="glossary.html#GLOSSARY-REPLICATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-REPLICATION" title="Replication">logical replication</a></em></a>
+     and <a class="glossterm" href="glossary.html#GLOSSARY-PARALLEL-QUERY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-PARALLEL-QUERY" title="Parallel query">parallel queries</a></em></a>.
+     In addition, <a class="glossterm" href="glossary.html#GLOSSARY-EXTENSION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-EXTENSION" title="Extension">Extensions</a></em></a> can add
+     custom background worker processes.
+   </p><p>
+    For more information, see
+    <a class="xref" href="bgworker.html" title="Chapter 48. Background Worker Processes">Chapter 48</a>.
+   </p></dd><dt id="GLOSSARY-BACKGROUND-WRITER"><span class="glossterm">Background writer (process)</span></dt><dd class="glossdef"><p>
+     An <a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC" title="Auxiliary process">auxiliary process</a></em></a>
+     that writes dirty
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATA-PAGE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATA-PAGE" title="Data page">data pages</a></em></a> from
+     <a class="glossterm" href="glossary.html#GLOSSARY-SHARED-MEMORY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SHARED-MEMORY" title="Shared memory">shared memory</a></em></a> to
+     the file system.  It wakes up periodically, but works only for a short
+     period in order to distribute its expensive <acronym class="acronym">I/O</acronym>
+     activity over time to avoid generating larger
+     <acronym class="acronym">I/O</acronym> peaks which could block other processes.
+    </p><p>
+     For more information, see
+     <a class="xref" href="runtime-config-resource.html#RUNTIME-CONFIG-RESOURCE-BACKGROUND-WRITER" title="20.4.5. Background Writer">Section 20.4.5</a>.
+    </p></dd><dt id="GLOSSARY-BASEBACKUP"><span class="glossterm">Base Backup</span></dt><dd class="glossdef"><p>
+     A binary copy of all
+     <a class="glossterm" href="glossary.html#GLOSSARY-DB-CLUSTER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DB-CLUSTER" title="Database cluster">database cluster</a></em></a>
+     files. It is generated by the tool <a class="xref" href="app-pgbasebackup.html" title="pg_basebackup"><span class="refentrytitle"><span class="application">pg_basebackup</span></span></a>.
+     In combination with WAL files it can be used as the starting point
+     for recovery, log shipping, or streaming replication.
+    </p></dd><dt id="GLOSSARY-BLOAT"><span class="glossterm">Bloat</span></dt><dd class="glossdef"><p>
+     Space in data pages which does not contain current row versions,
+     such as unused (free) space or outdated row versions.
+    </p></dd><dt id="GLOSSARY-CAST"><span class="glossterm">Cast</span></dt><dd class="glossdef"><p>
+     A conversion of a <a class="glossterm" href="glossary.html#GLOSSARY-DATUM"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATUM" title="Datum">datum</a></em></a>
+     from its current data type to another data type.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createcast.html" title="CREATE CAST"><span class="refentrytitle">CREATE CAST</span></a>.
+    </p></dd><dt id="GLOSSARY-CATALOG"><span class="glossterm">Catalog</span></dt><dd class="glossdef"><p>
+     The <acronym class="acronym">SQL</acronym> standard uses this term to
+     indicate what is called a
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a> in
+     <span class="productname">PostgreSQL</span>'s terminology.
+    </p><p>
+     (Don't confuse this term with
+     <a class="glossterm" href="glossary.html#GLOSSARY-SYSTEM-CATALOG"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SYSTEM-CATALOG" title="System catalog">system catalog</a></em></a>).
+    </p><p>
+     For more information, see
+     <a class="xref" href="manage-ag-overview.html" title="23.1. Overview">Section 23.1</a>.
+    </p></dd><dt id="GLOSSARY-CHECK-CONSTRAINT"><span class="glossterm">Check constraint</span></dt><dd class="glossdef"><p>
+     A type of <a class="glossterm" href="glossary.html#GLOSSARY-CONSTRAINT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CONSTRAINT" title="Constraint">constraint</a></em></a>
+     defined on a <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a>
+     which restricts the values allowed in one or more
+     <a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE" title="Attribute">attributes</a></em></a>. The
+     check constraint can make reference to any attribute of the same row in
+     the relation, but cannot reference other rows of the same relation or
+     other relations.
+    </p><p>
+     For more information, see
+     <a class="xref" href="ddl-constraints.html" title="5.4. Constraints">Section 5.4</a>.
+    </p></dd><dt id="GLOSSARY-CHECKPOINT"><span class="glossterm">Checkpoint</span></dt><dd class="glossdef"><p>
+     A point in the <a class="glossterm" href="glossary.html#GLOSSARY-WAL"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL" title="Write-ahead log">WAL</a></em></a> sequence
+     at which it is guaranteed that the heap and index data files have been
+     updated with all information from
+     <a class="glossterm" href="glossary.html#GLOSSARY-SHARED-MEMORY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SHARED-MEMORY" title="Shared memory">shared memory</a></em></a>
+     modified before that checkpoint;
+     a <em class="firstterm">checkpoint record</em> is written and flushed to WAL
+     to mark that point.
+    </p><p>
+     A checkpoint is also the act of carrying out all the actions that
+     are necessary to reach a checkpoint as defined above.
+     This process is initiated when predefined conditions are met,
+     such as a specified amount of time has passed, or a certain volume
+     of records has been written; or it can be invoked by the user
+     with the command <code class="command">CHECKPOINT</code>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="wal-configuration.html" title="30.5. WAL Configuration">Section 30.5</a>.
+    </p></dd><dt id="GLOSSARY-CHECKPOINTER"><span class="glossterm">Checkpointer (process)</span></dt><dd class="glossdef"><p>
+     An <a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC" title="Auxiliary process">auxiliary process</a></em></a>
+     that is responsible for executing
+     <a class="glossterm" href="glossary.html#GLOSSARY-CHECKPOINT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CHECKPOINT" title="Checkpoint">checkpoints</a></em></a>.
+    </p></dd><dt><span class="glossterm">Class (archaic)</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-RELATION">Relation</a>.</p></dd><dt id="GLOSSARY-CLIENT"><span class="glossterm">Client (process)</span></dt><dd class="glossdef"><p>
+     Any process, possibly remote, that establishes a
+     <a class="glossterm" href="glossary.html#GLOSSARY-SESSION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SESSION" title="Session">session</a></em></a>
+     by <a class="glossterm" href="glossary.html#GLOSSARY-CONNECTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CONNECTION" title="Connection">connecting</a></em></a> to an
+     <a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE" title="Instance">instance</a></em></a>
+     to interact with a <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a>.
+    </p></dd><dt id="GLOSSARY-COLUMN"><span class="glossterm">Column</span></dt><dd class="glossdef"><p>
+     An <a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE" title="Attribute">attribute</a></em></a> found in
+     a <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a> or
+     <a class="glossterm" href="glossary.html#GLOSSARY-VIEW"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-VIEW" title="View">view</a></em></a>.
+    </p></dd><dt id="GLOSSARY-COMMIT"><span class="glossterm">Commit</span></dt><dd class="glossdef"><p>
+     The act of finalizing a
+     <a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION" title="Transaction">transaction</a></em></a> within
+     the <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a>, which
+     makes it visible to other transactions and assures its
+     <a class="glossterm" href="glossary.html#GLOSSARY-DURABILITY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DURABILITY" title="Durability">durability</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-commit.html" title="COMMIT"><span class="refentrytitle">COMMIT</span></a>.
+    </p></dd><dt id="GLOSSARY-CONCURRENCY"><span class="glossterm">Concurrency</span></dt><dd class="glossdef"><p>
+     The concept that multiple independent operations happen within the
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a> at the same time.
+     In <span class="productname">PostgreSQL</span>, concurrency is controlled by
+     the <a class="glossterm" href="glossary.html#GLOSSARY-MVCC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-MVCC" title="Multi-version concurrency control (MVCC)">multiversion concurrency control</a></em></a>
+     mechanism.
+    </p></dd><dt id="GLOSSARY-CONNECTION"><span class="glossterm">Connection</span></dt><dd class="glossdef"><p>
+     An established line of communication between a client process and a
+     <a class="glossterm" href="glossary.html#GLOSSARY-BACKEND"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-BACKEND" title="Backend (process)">backend</a></em></a> process,
+     usually over a network, supporting a
+     <a class="glossterm" href="glossary.html#GLOSSARY-SESSION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SESSION" title="Session">session</a></em></a>.  This term is
+     sometimes used as a synonym for session.
+    </p><p>
+     For more information, see
+     <a class="xref" href="runtime-config-connection.html" title="20.3. Connections and Authentication">Section 20.3</a>.
+    </p></dd><dt id="GLOSSARY-CONSISTENCY"><span class="glossterm">Consistency</span></dt><dd class="glossdef"><p>
+     The property that the data in the
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a>
+     is always in compliance with
+     <a class="glossterm" href="glossary.html#GLOSSARY-CONSTRAINT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CONSTRAINT" title="Constraint">integrity constraints</a></em></a>.
+     Transactions may be allowed to violate some of the constraints
+     transiently before it commits, but if such violations are not resolved
+     by the time it commits, such a transaction is automatically
+     <a class="glossterm" href="glossary.html#GLOSSARY-ROLLBACK"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ROLLBACK" title="Rollback">rolled back</a></em></a>.
+     This is one of the <acronym class="acronym">ACID</acronym> properties.
+    </p></dd><dt id="GLOSSARY-CONSTRAINT"><span class="glossterm">Constraint</span></dt><dd class="glossdef"><p>
+     A restriction on the values of data allowed within a
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a>,
+     or in attributes of a
+     <a class="glossterm" href="glossary.html#GLOSSARY-DOMAIN"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DOMAIN" title="Domain">domain</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="ddl-constraints.html" title="5.4. Constraints">Section 5.4</a>.
+    </p></dd><dt id="GLOSSARY-CUMULATIVE-STATISTICS"><span class="glossterm">Cumulative Statistics System</span></dt><dd class="glossdef"><p>
+     A system which, if enabled, accumulates statistical information
+     about the <a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE" title="Instance">instance</a></em></a>'s
+     activities.
+    </p><p>
+      For more information, see
+      <a class="xref" href="monitoring-stats.html" title="28.2. The Cumulative Statistics System">Section 28.2</a>.
+    </p></dd><dt><span class="glossterm">Data area</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-DATA-DIRECTORY">Data directory</a>.</p></dd><dt id="GLOSSARY-DATABASE"><span class="glossterm">Database</span></dt><dd class="glossdef"><p>
+     A named collection of
+     <a class="glossterm" href="glossary.html#GLOSSARY-SQL-OBJECT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SQL-OBJECT" title="SQL object">local SQL objects</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="manage-ag-overview.html" title="23.1. Overview">Section 23.1</a>.
+    </p></dd><dt id="GLOSSARY-DB-CLUSTER"><span class="glossterm">Database cluster</span></dt><dd class="glossdef"><p>
+     A collection of databases and global SQL objects,
+     and their common static and dynamic metadata.
+     Sometimes referred to as a
+     <em class="firstterm">cluster</em>.
+    </p><p>
+     In <span class="productname">PostgreSQL</span>, the term
+     <em class="firstterm">cluster</em> is also sometimes used to refer to an instance.
+     (Don't confuse this term with the SQL command <code class="command">CLUSTER</code>.)
+    </p></dd><dt><span class="glossterm">Database server</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-INSTANCE">Instance</a>.</p></dd><dt id="GLOSSARY-DATA-DIRECTORY"><span class="glossterm">Data directory</span></dt><dd class="glossdef"><p>
+     The base directory on the file system of a
+     <a class="glossterm" href="glossary.html#GLOSSARY-SERVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SERVER" title="Server">server</a></em></a> that contains all
+     data files and subdirectories associated with a
+     <a class="glossterm" href="glossary.html#GLOSSARY-DB-CLUSTER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DB-CLUSTER" title="Database cluster">database cluster</a></em></a>
+     (with the exception of
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLESPACE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLESPACE" title="Tablespace">tablespaces</a></em></a>,
+     and optionally <a class="glossterm" href="glossary.html#GLOSSARY-WAL"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL" title="Write-ahead log">WAL</a></em></a>).
+     The environment variable <code class="literal">PGDATA</code> is commonly used to
+     refer to the data directory.
+    </p><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-DB-CLUSTER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DB-CLUSTER" title="Database cluster">cluster</a></em></a>'s storage
+     space comprises the data directory plus any additional tablespaces.
+    </p><p>
+     For more information, see
+     <a class="xref" href="storage-file-layout.html" title="73.1. Database File Layout">Section 73.1</a>.
+    </p></dd><dt id="GLOSSARY-DATA-PAGE"><span class="glossterm">Data page</span></dt><dd class="glossdef"><p>
+     The basic structure used to store relation data.
+     All pages are of the same size.
+     Data pages are typically stored on disk, each in a specific file,
+     and can be read to <a class="glossterm" href="glossary.html#GLOSSARY-SHARED-MEMORY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SHARED-MEMORY" title="Shared memory">shared buffers</a></em></a>
+     where they can be modified, becoming
+     <em class="firstterm">dirty</em>.  They become clean when written
+     to disk.  New pages, which initially exist in memory only, are also
+     dirty until written.
+    </p></dd><dt id="GLOSSARY-DATUM"><span class="glossterm">Datum</span></dt><dd class="glossdef"><p>
+     The internal representation of one value of an <acronym class="acronym">SQL</acronym>
+     data type.
+    </p></dd><dt id="GLOSSARY-DELETE"><span class="glossterm">Delete</span></dt><dd class="glossdef"><p>
+     An <acronym class="acronym">SQL</acronym> command which removes
+     <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">rows</a></em></a> from a given
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a>
+     or <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-delete.html" title="DELETE"><span class="refentrytitle">DELETE</span></a>.
+    </p></dd><dt id="GLOSSARY-DOMAIN"><span class="glossterm">Domain</span></dt><dd class="glossdef"><p>
+     A user-defined data type that is based on another underlying data type.
+     It acts the same as the underlying type except for possibly restricting
+     the set of allowed values.
+    </p><p>
+     For more information, see <a class="xref" href="domains.html" title="8.18. Domain Types">Section 8.18</a>.
+    </p></dd><dt id="GLOSSARY-DURABILITY"><span class="glossterm">Durability</span></dt><dd class="glossdef"><p>
+     The assurance that once a
+     <a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION" title="Transaction">transaction</a></em></a> has
+     been <a class="glossterm" href="glossary.html#GLOSSARY-COMMIT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-COMMIT" title="Commit">committed</a></em></a>, the
+     changes remain even after a system failure or crash.
+     This is one of the <acronym class="acronym">ACID</acronym> properties.
+    </p></dd><dt><span class="glossterm">Epoch</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-XID">Transaction ID</a>.</p></dd><dt id="GLOSSARY-EXTENSION"><span class="glossterm">Extension</span></dt><dd class="glossdef"><p>
+     A software add-on package that can be installed on an
+     <a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE" title="Instance">instance</a></em></a> to
+     get extra features.
+    </p><p>
+     For more information, see
+     <a class="xref" href="extend-extensions.html" title="38.17. Packaging Related Objects into an Extension">Section 38.17</a>.
+    </p></dd><dt id="GLOSSARY-FILE-SEGMENT"><span class="glossterm">File segment</span></dt><dd class="glossdef"><p>
+     A physical file which stores data for a given
+     <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a>.
+     File segments are limited in size by a configuration value
+     (typically 1 gigabyte),
+     so if a relation exceeds that size, it is split into multiple segments.
+    </p><p>
+     For more information, see
+     <a class="xref" href="storage-file-layout.html" title="73.1. Database File Layout">Section 73.1</a>.
+    </p><p>
+     (Don't confuse this term with the similar term
+     <a class="glossterm" href="glossary.html#GLOSSARY-WAL-FILE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-FILE" title="WAL file">WAL segment</a></em></a>).
+    </p></dd><dt id="GLOSSARY-FOREIGN-DATA-WRAPPER"><span class="glossterm">Foreign data wrapper</span></dt><dd class="glossdef"><p>
+     A means of representing data that is not contained in the local
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a> so that it appears as if were in local
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table(s)</a></em></a>. With a foreign data wrapper it is
+     possible to define a <a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-SERVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-SERVER" title="Foreign server">foreign server</a></em></a> and
+     <a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-TABLE" title="Foreign table (relation)">foreign tables</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createforeigndatawrapper.html" title="CREATE FOREIGN DATA WRAPPER"><span class="refentrytitle">CREATE FOREIGN DATA WRAPPER</span></a>.
+    </p></dd><dt id="GLOSSARY-FOREIGN-KEY"><span class="glossterm">Foreign key</span></dt><dd class="glossdef"><p>
+     A type of <a class="glossterm" href="glossary.html#GLOSSARY-CONSTRAINT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CONSTRAINT" title="Constraint">constraint</a></em></a>
+     defined on one or more <a class="glossterm" href="glossary.html#GLOSSARY-COLUMN"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-COLUMN" title="Column">columns</a></em></a>
+     in a <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a> which
+     requires the value(s) in those <a class="glossterm" href="glossary.html#GLOSSARY-COLUMN"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-COLUMN" title="Column">columns</a></em></a> to
+     identify zero or one <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">row</a></em></a>
+     in another (or, infrequently, the same)
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a>.
+    </p></dd><dt id="GLOSSARY-FOREIGN-SERVER"><span class="glossterm">Foreign server</span></dt><dd class="glossdef"><p>
+     A named collection of
+     <a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-TABLE" title="Foreign table (relation)">foreign tables</a></em></a> which
+     all use the same
+     <a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-DATA-WRAPPER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-DATA-WRAPPER" title="Foreign data wrapper">foreign data wrapper</a></em></a>
+     and have other configuration values in common.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createserver.html" title="CREATE SERVER"><span class="refentrytitle">CREATE SERVER</span></a>.
+    </p></dd><dt id="GLOSSARY-FOREIGN-TABLE"><span class="glossterm">Foreign table (relation)</span></dt><dd class="glossdef"><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a> which appears to have
+     <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">rows</a></em></a> and
+     <a class="glossterm" href="glossary.html#GLOSSARY-COLUMN"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-COLUMN" title="Column">columns</a></em></a> similar to a
+     regular <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a>, but will forward
+     requests for data through its
+     <a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-DATA-WRAPPER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-DATA-WRAPPER" title="Foreign data wrapper">foreign data wrapper</a></em></a>,
+     which will return <a class="glossterm" href="glossary.html#GLOSSARY-RESULT-SET"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RESULT-SET" title="Result set">result sets</a></em></a>
+     structured according to the definition of the
+     <a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-TABLE" title="Foreign table (relation)">foreign table</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createforeigntable.html" title="CREATE FOREIGN TABLE"><span class="refentrytitle">CREATE FOREIGN TABLE</span></a>.
+    </p></dd><dt id="GLOSSARY-FORK"><span class="glossterm">Fork</span></dt><dd class="glossdef"><p>
+     Each of the separate segmented file sets in which a relation is stored.
+     The <em class="firstterm">main fork</em> is where the actual data resides.
+     There also exist two secondary forks for metadata:
+     the <a class="glossterm" href="glossary.html#GLOSSARY-FSM"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FSM" title="Free space map (fork)">free space map</a></em></a>
+     and the <a class="glossterm" href="glossary.html#GLOSSARY-VM"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-VM" title="Visibility map (fork)">visibility map</a></em></a>.
+     <a class="glossterm" href="glossary.html#GLOSSARY-UNLOGGED"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-UNLOGGED" title="Unlogged">Unlogged relations</a></em></a>
+     also have an <em class="firstterm">init fork</em>.
+    </p></dd><dt id="GLOSSARY-FSM"><span class="glossterm">Free space map (fork)</span></dt><dd class="glossdef"><p>
+     A storage structure that keeps metadata about each data page of a table's
+     main fork.  The free space map entry for each page stores the
+     amount of free space that's available for future tuples, and is structured
+     to be efficiently searched for available space for a new tuple of a given
+     size.
+    </p><p>
+     For more information, see
+     <a class="xref" href="storage-fsm.html" title="73.3. Free Space Map">Section 73.3</a>.
+    </p></dd><dt id="GLOSSARY-FUNCTION"><span class="glossterm">Function (routine)</span></dt><dd class="glossdef"><p>
+     A type of routine that receives zero or more arguments, returns zero or more
+     output values, and is constrained to run within one transaction.
+     Functions are invoked as part of a query, for example via
+     <code class="command">SELECT</code>.
+     Certain functions can return
+     <a class="glossterm" href="glossary.html#GLOSSARY-RESULT-SET"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RESULT-SET" title="Result set">sets</a></em></a>; those are
+     called <em class="firstterm">set-returning functions</em>.
+    </p><p>
+     Functions can also be used for
+     <a class="glossterm" href="glossary.html#GLOSSARY-TRIGGER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TRIGGER" title="Trigger">triggers</a></em></a> to invoke.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createfunction.html" title="CREATE FUNCTION"><span class="refentrytitle">CREATE FUNCTION</span></a>.
+    </p></dd><dt id="GLOSSARY-GRANT"><span class="glossterm">Grant</span></dt><dd class="glossdef"><p>
+     An <acronym class="acronym">SQL</acronym> command that is used to allow a
+     <a class="glossterm" href="glossary.html#GLOSSARY-USER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-USER" title="User">user</a></em></a> or
+     <a class="glossterm" href="glossary.html#GLOSSARY-ROLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ROLE" title="Role">role</a></em></a> to access
+     specific objects within the <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-grant.html" title="GRANT"><span class="refentrytitle">GRANT</span></a>.
+    </p></dd><dt id="GLOSSARY-HEAP"><span class="glossterm">Heap</span></dt><dd class="glossdef"><p>
+     Contains the values of <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">row</a></em></a>
+     attributes (i.e., the data) for a
+     <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a>.
+     The heap is realized within one or more
+     <a class="glossterm" href="glossary.html#GLOSSARY-FILE-SEGMENT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FILE-SEGMENT" title="File segment">file segments</a></em></a>
+     in the relation's <a class="glossterm" href="glossary.html#GLOSSARY-FORK"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FORK" title="Fork">main fork</a></em></a>.
+    </p></dd><dt id="GLOSSARY-HOST"><span class="glossterm">Host</span></dt><dd class="glossdef"><p>
+     A computer that communicates with other computers over a network.
+     This is sometimes used as a synonym for
+     <a class="glossterm" href="glossary.html#GLOSSARY-SERVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SERVER" title="Server">server</a></em></a>.
+     It is also used to refer to a computer where
+     <a class="glossterm" href="glossary.html#GLOSSARY-CLIENT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CLIENT" title="Client (process)">client processes</a></em></a> run.
+    </p></dd><dt id="GLOSSARY-INDEX"><span class="glossterm">Index (relation)</span></dt><dd class="glossdef"><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a> that contains
+     data derived from a <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a>
+     or <a class="glossterm" href="glossary.html#GLOSSARY-MATERIALIZED-VIEW"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-MATERIALIZED-VIEW" title="Materialized view (relation)">materialized view</a></em></a>.
+     Its internal structure supports fast retrieval of and access to the original
+     data.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createindex.html" title="CREATE INDEX"><span class="refentrytitle">CREATE INDEX</span></a>.
+    </p></dd><dt id="GLOSSARY-INSERT"><span class="glossterm">Insert</span></dt><dd class="glossdef"><p>
+     An <acronym class="acronym">SQL</acronym> command used to add new data into a
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-insert.html" title="INSERT"><span class="refentrytitle">INSERT</span></a>.
+    </p></dd><dt id="GLOSSARY-INSTANCE"><span class="glossterm">Instance</span></dt><dd class="glossdef"><p>
+     A group of <a class="glossterm" href="glossary.html#GLOSSARY-BACKEND"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-BACKEND" title="Backend (process)">backend</a></em></a> and
+     <a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC" title="Auxiliary process">auxiliary processes</a></em></a>
+     that communicate using a common shared memory area.  One
+     <a class="glossterm" href="glossary.html#GLOSSARY-POSTMASTER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-POSTMASTER" title="Postmaster (process)">postmaster process</a></em></a>
+     manages the instance; one instance manages exactly one
+     <a class="glossterm" href="glossary.html#GLOSSARY-DB-CLUSTER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DB-CLUSTER" title="Database cluster">database cluster</a></em></a>
+     with all its databases.  Many instances can run on the same
+     <a class="glossterm" href="glossary.html#GLOSSARY-SERVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SERVER" title="Server">server</a></em></a>
+     as long as their <acronym class="acronym">TCP</acronym> ports do not conflict.
+    </p><p>
+     The instance handles all key features of a <acronym class="acronym">DBMS</acronym>:
+     read and write access to files and shared memory,
+     assurance of the <acronym class="acronym">ACID</acronym> properties,
+     <a class="glossterm" href="glossary.html#GLOSSARY-CONNECTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CONNECTION" title="Connection">connections</a></em></a> to
+     <a class="glossterm" href="glossary.html#GLOSSARY-CLIENT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CLIENT" title="Client (process)">client processes</a></em></a>,
+     privilege verification, crash recovery, replication, etc.
+    </p></dd><dt id="GLOSSARY-ISOLATION"><span class="glossterm">Isolation</span></dt><dd class="glossdef"><p>
+     The property that the effects of a transaction are not visible to
+     <a class="glossterm" href="glossary.html#GLOSSARY-CONCURRENCY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CONCURRENCY" title="Concurrency">concurrent transactions</a></em></a>
+     before it commits.
+     This is one of the <acronym class="acronym">ACID</acronym> properties.
+    </p><p>
+     For more information, see <a class="xref" href="transaction-iso.html" title="13.2. Transaction Isolation">Section 13.2</a>.
+    </p></dd><dt id="GLOSSARY-JOIN"><span class="glossterm">Join</span></dt><dd class="glossdef"><p>
+     An operation and <acronym class="acronym">SQL</acronym> keyword used in
+     <a class="glossterm" href="glossary.html#GLOSSARY-QUERY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-QUERY" title="Query">queries</a></em></a>
+     for combining data from multiple
+     <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relations</a></em></a>.
+    </p></dd><dt id="GLOSSARY-KEY"><span class="glossterm">Key</span></dt><dd class="glossdef"><p>
+     A means of identifying a <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">row</a></em></a> within a
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a> or
+     other <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a> by
+     values contained within one or more
+     <a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE" title="Attribute">attributes</a></em></a>
+     in that relation.
+    </p></dd><dt id="GLOSSARY-LOCK"><span class="glossterm">Lock</span></dt><dd class="glossdef"><p>
+     A mechanism that allows a process to limit or prevent simultaneous
+     access to a resource.
+    </p></dd><dt id="GLOSSARY-LOG-FILE"><span class="glossterm">Log file</span></dt><dd class="glossdef"><p>
+     Log files contain human-readable text lines about events.
+     Examples include login failures, long-running queries, etc.
+    </p><p>
+     For more information, see
+     <a class="xref" href="logfile-maintenance.html" title="25.3. Log File Maintenance">Section 25.3</a>.
+    </p></dd><dt id="GLOSSARY-LOGGED"><span class="glossterm">Logged</span></dt><dd class="glossdef"><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a> is considered
+     <a class="glossterm" href="glossary.html#GLOSSARY-LOGGED"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-LOGGED" title="Logged">logged</a></em></a> if changes to it are sent to the
+     <a class="glossterm" href="glossary.html#GLOSSARY-WAL"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL" title="Write-ahead log">WAL</a></em></a>. By default, all regular
+     tables are logged. A table can be specified as
+     <a class="glossterm" href="glossary.html#GLOSSARY-UNLOGGED"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-UNLOGGED" title="Unlogged">unlogged</a></em></a> either at
+     creation time or via the <code class="command">ALTER TABLE</code> command.
+    </p></dd><dt id="GLOSSARY-LOGGER"><span class="glossterm">Logger (process)</span></dt><dd class="glossdef"><p>
+     An <a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC" title="Auxiliary process">auxiliary process</a></em></a>
+     which, if enabled, writes information about database events into the current
+     <a class="glossterm" href="glossary.html#GLOSSARY-LOG-FILE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-LOG-FILE" title="Log file">log file</a></em></a>.
+     When reaching certain time- or
+     volume-dependent criteria, a new log file is created.
+     Also called <em class="firstterm">syslogger</em>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="runtime-config-logging.html" title="20.8. Error Reporting and Logging">Section 20.8</a>.
+    </p></dd><dt id="GLOSSARY-LOG-RECORD"><span class="glossterm">Log record</span></dt><dd class="glossdef"><p>
+      Archaic term for a <a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECORD"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECORD" title="WAL record">WAL record</a></em></a>.
+     </p></dd><dt><span class="glossterm">Master (server)</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-PRIMARY-SERVER">Primary (server)</a>.</p></dd><dt id="GLOSSARY-MATERIALIZED"><span class="glossterm">Materialized</span></dt><dd class="glossdef"><p>
+     The property that some information has been pre-computed and stored
+     for later use, rather than computing it on-the-fly.
+    </p><p>
+     This term is used in
+     <a class="glossterm" href="glossary.html#GLOSSARY-MATERIALIZED-VIEW"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-MATERIALIZED-VIEW" title="Materialized view (relation)">materialized view</a></em></a>,
+     to mean that the data derived from the view's query is stored on
+     disk separately from the sources of that data.
+    </p><p>
+     This term is also used to refer to some multi-step queries to mean that
+     the data resulting from executing a given step is stored in memory
+     (with the possibility of spilling to disk), so that it can be read multiple
+     times by another step.
+    </p></dd><dt id="GLOSSARY-MATERIALIZED-VIEW"><span class="glossterm">Materialized view (relation)</span></dt><dd class="glossdef"><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a> that is
+     defined by a <code class="command">SELECT</code> statement
+     (just like a <a class="glossterm" href="glossary.html#GLOSSARY-VIEW"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-VIEW" title="View">view</a></em></a>),
+     but stores data in the same way that a
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a> does. It cannot be
+     modified via <code class="command">INSERT</code>, <code class="command">UPDATE</code>, or
+     <code class="command">DELETE</code> operations.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-creatematerializedview.html" title="CREATE MATERIALIZED VIEW"><span class="refentrytitle">CREATE MATERIALIZED VIEW</span></a>.
+    </p></dd><dt id="GLOSSARY-MVCC"><span class="glossterm">Multi-version concurrency control (MVCC)</span></dt><dd class="glossdef"><p>
+     A mechanism designed to allow several
+     <a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION" title="Transaction">transactions</a></em></a> to be
+     reading and writing the same rows without one process causing other
+     processes to stall.
+     In <span class="productname">PostgreSQL</span>, MVCC is implemented by
+     creating copies (<em class="firstterm">versions</em>) of
+     <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">tuples</a></em></a> as they are
+     modified; after transactions that can see the old versions terminate,
+     those old versions need to be removed.
+    </p></dd><dt id="GLOSSARY-NULL"><span class="glossterm">Null</span></dt><dd class="glossdef"><p>
+     A concept of non-existence that is a central tenet of relational
+     database theory. It represents the absence of a definite value.
+    </p></dd><dt><span class="glossterm">Optimizer</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-PLANNER">Query planner</a>.</p></dd><dt id="GLOSSARY-PARALLEL-QUERY"><span class="glossterm">Parallel query</span></dt><dd class="glossdef"><p>
+     The ability to handle parts of executing a
+     <a class="glossterm" href="glossary.html#GLOSSARY-QUERY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-QUERY" title="Query">query</a></em></a> to take advantage
+     of parallel processes on servers with multiple <acronym class="acronym">CPU</acronym>s.
+    </p></dd><dt id="GLOSSARY-PARTITION"><span class="glossterm">Partition</span></dt><dd class="glossdef"><p>
+     One of several disjoint (not overlapping) subsets of a larger set.
+    </p></dd><dd class="glossdef"><p>
+     In reference to a
+     <a class="glossterm" href="glossary.html#GLOSSARY-PARTITIONED-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-PARTITIONED-TABLE" title="Partitioned table (relation)">partitioned table</a></em></a>:
+     One of the tables that each contain part of the data of the partitioned table,
+     which is said to be the <em class="firstterm">parent</em>.
+     The partition is itself a table, so it can also be queried directly;
+     at the same time, a partition can sometimes be a partitioned table,
+     allowing hierarchies to be created.
+    </p></dd><dd class="glossdef"><p>
+     In reference to a <a class="glossterm" href="glossary.html#GLOSSARY-WINDOW-FUNCTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WINDOW-FUNCTION" title="Window function (routine)">window function</a></em></a>
+     in a <a class="glossterm" href="glossary.html#GLOSSARY-QUERY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-QUERY" title="Query">query</a></em></a>,
+     a partition is a user-defined criterion that identifies which neighboring
+     <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">rows</a></em></a>
+     of the <a class="glossterm" href="glossary.html#GLOSSARY-RESULT-SET"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RESULT-SET" title="Result set">query's result set</a></em></a>
+     can be considered by the function.
+    </p></dd><dt id="GLOSSARY-PARTITIONED-TABLE"><span class="glossterm">Partitioned table (relation)</span></dt><dd class="glossdef"><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a> that is
+     in semantic terms the same as a <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a>,
+     but whose storage is distributed across several
+     <a class="glossterm" href="glossary.html#GLOSSARY-PARTITION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-PARTITION" title="Partition">partitions</a></em></a>.
+    </p></dd><dt id="GLOSSARY-POSTMASTER"><span class="glossterm">Postmaster (process)</span></dt><dd class="glossdef"><p>
+      The very first process of an <a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE" title="Instance">instance</a></em></a>.
+      It starts and manages the
+      <a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC" title="Auxiliary process">auxiliary processes</a></em></a>
+      and creates <a class="glossterm" href="glossary.html#GLOSSARY-BACKEND"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-BACKEND" title="Backend (process)">backend processes</a></em></a>
+      on demand.
+    </p><p>
+     For more information, see
+     <a class="xref" href="server-start.html" title="19.3. Starting the Database Server">Section 19.3</a>.
+    </p></dd><dt id="GLOSSARY-PRIMARY-KEY"><span class="glossterm">Primary key</span></dt><dd class="glossdef"><p>
+     A special case of a
+     <a class="glossterm" href="glossary.html#GLOSSARY-UNIQUE-CONSTRAINT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-UNIQUE-CONSTRAINT" title="Unique constraint">unique constraint</a></em></a>
+     defined on a
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a> or other
+     <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a> that also
+     guarantees that all of the
+     <a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE" title="Attribute">attributes</a></em></a>
+     within the <a class="glossterm" href="glossary.html#GLOSSARY-PRIMARY-KEY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-PRIMARY-KEY" title="Primary key">primary key</a></em></a>
+     do not have <a class="glossterm" href="glossary.html#GLOSSARY-NULL"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-NULL" title="Null">null</a></em></a> values.
+     As the name implies, there can be only one
+     primary key per table, though it is possible to have multiple unique
+     constraints that also have no null-capable attributes.
+    </p></dd><dt id="GLOSSARY-PRIMARY-SERVER"><span class="glossterm">Primary (server)</span></dt><dd class="glossdef"><p>
+     When two or more <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">databases</a></em></a>
+     are linked via <a class="glossterm" href="glossary.html#GLOSSARY-REPLICATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-REPLICATION" title="Replication">replication</a></em></a>,
+     the <a class="glossterm" href="glossary.html#GLOSSARY-SERVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SERVER" title="Server">server</a></em></a>
+     that is considered the authoritative source of information is called
+     the <em class="firstterm">primary</em>,
+     also known as a <em class="firstterm">master</em>.
+    </p></dd><dt id="GLOSSARY-PROCEDURE"><span class="glossterm">Procedure (routine)</span></dt><dd class="glossdef"><p>
+     A type of routine.
+     Their distinctive qualities are that they do not return values,
+     and that they are allowed to make transactional statements such
+     as <code class="command">COMMIT</code> and <code class="command">ROLLBACK</code>.
+     They are invoked via the <code class="command">CALL</code> command.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createprocedure.html" title="CREATE PROCEDURE"><span class="refentrytitle">CREATE PROCEDURE</span></a>.
+    </p></dd><dt id="GLOSSARY-QUERY"><span class="glossterm">Query</span></dt><dd class="glossdef"><p>
+     A request sent by a client to a <a class="glossterm" href="glossary.html#GLOSSARY-BACKEND"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-BACKEND" title="Backend (process)">backend</a></em></a>,
+     usually to return results or to modify data on the database.
+    </p></dd><dt id="GLOSSARY-PLANNER"><span class="glossterm">Query planner</span></dt><dd class="glossdef"><p>
+     The part of <span class="productname">PostgreSQL</span> that is devoted to
+     determining (<em class="firstterm">planning</em>) the most efficient way to
+     execute <a class="glossterm" href="glossary.html#GLOSSARY-QUERY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-QUERY" title="Query">queries</a></em></a>.
+     Also known as <em class="firstterm">query optimizer</em>,
+     <em class="firstterm">optimizer</em>, or simply <em class="firstterm">planner</em>.
+    </p></dd><dt><span class="glossterm">Record</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-TUPLE">Tuple</a>.</p></dd><dt><span class="glossterm">Recycling</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-WAL-FILE">WAL file</a>.</p></dd><dt id="GLOSSARY-REFERENTIAL-INTEGRITY"><span class="glossterm">Referential integrity</span></dt><dd class="glossdef"><p>
+     A means of restricting data in one <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a>
+     by a <a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-KEY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-KEY" title="Foreign key">foreign key</a></em></a>
+     so that it must have matching data in another
+     <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a>.
+    </p></dd><dt id="GLOSSARY-RELATION"><span class="glossterm">Relation</span></dt><dd class="glossdef"><p>
+     The generic term for all objects in a
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a>
+     that have a name and a list of
+     <a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE" title="Attribute">attributes</a></em></a>
+     defined in a specific order.
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">Tables</a></em></a>,
+     <a class="glossterm" href="glossary.html#GLOSSARY-SEQUENCE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SEQUENCE" title="Sequence (relation)">sequences</a></em></a>,
+     <a class="glossterm" href="glossary.html#GLOSSARY-VIEW"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-VIEW" title="View">views</a></em></a>,
+     <a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-TABLE" title="Foreign table (relation)">foreign tables</a></em></a>,
+     <a class="glossterm" href="glossary.html#GLOSSARY-MATERIALIZED-VIEW"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-MATERIALIZED-VIEW" title="Materialized view (relation)">materialized views</a></em></a>,
+     composite types, and
+     <a class="glossterm" href="glossary.html#GLOSSARY-INDEX"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-INDEX" title="Index (relation)">indexes</a></em></a> are all relations.
+    </p><p>
+     More generically, a relation is a set of tuples; for example,
+     the result of a query is also a relation.
+    </p><p>
+     In <span class="productname">PostgreSQL</span>,
+     <em class="firstterm">Class</em> is an archaic synonym for
+     <em class="firstterm">relation</em>.
+    </p></dd><dt id="GLOSSARY-REPLICA"><span class="glossterm">Replica (server)</span></dt><dd class="glossdef"><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a> that is paired
+     with a <a class="glossterm" href="glossary.html#GLOSSARY-PRIMARY-SERVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-PRIMARY-SERVER" title="Primary (server)">primary</a></em></a>
+     database and is maintaining a copy of some or all of the primary database's
+     data. The foremost reasons for doing this are to allow for greater access
+     to that data, and to maintain availability of the data in the event that
+     the <a class="glossterm" href="glossary.html#GLOSSARY-PRIMARY-SERVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-PRIMARY-SERVER" title="Primary (server)">primary</a></em></a>
+     becomes unavailable.
+    </p></dd><dt id="GLOSSARY-REPLICATION"><span class="glossterm">Replication</span></dt><dd class="glossdef"><p>
+     The act of reproducing data on one
+     <a class="glossterm" href="glossary.html#GLOSSARY-SERVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SERVER" title="Server">server</a></em></a> onto another
+     server called a <a class="glossterm" href="glossary.html#GLOSSARY-REPLICA"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-REPLICA" title="Replica (server)">replica</a></em></a>.
+     This can take the form of <em class="firstterm">physical replication</em>,
+     where all file changes from one server are copied verbatim,
+     or <em class="firstterm">logical replication</em> where a defined subset
+     of data changes are conveyed using a higher-level representation.
+    </p></dd><dt id="GLOSSARY-RESULT-SET"><span class="glossterm">Result set</span></dt><dd class="glossdef"><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a> transmitted
+     from a <a class="glossterm" href="glossary.html#GLOSSARY-BACKEND"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-BACKEND" title="Backend (process)">backend process</a></em></a>
+     to a <a class="glossterm" href="glossary.html#GLOSSARY-CLIENT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CLIENT" title="Client (process)">client</a></em></a> upon the
+     completion of an <acronym class="acronym">SQL</acronym> command, usually a
+     <code class="command">SELECT</code> but it can be an
+     <code class="command">INSERT</code>, <code class="command">UPDATE</code>, or
+     <code class="command">DELETE</code> command if the <code class="literal">RETURNING</code>
+     clause is specified.
+    </p><p>
+     The fact that a result set is a relation means that a query can be used
+     in the definition of another query, becoming a
+     <em class="firstterm">subquery</em>.
+    </p></dd><dd class="glossdef"><p>
+    </p></dd><dt id="GLOSSARY-REVOKE"><span class="glossterm">Revoke</span></dt><dd class="glossdef"><p>
+     A command to prevent access to a named set of
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a> objects for a
+     named list of <a class="glossterm" href="glossary.html#GLOSSARY-ROLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ROLE" title="Role">roles</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-revoke.html" title="REVOKE"><span class="refentrytitle">REVOKE</span></a>.
+    </p></dd><dt id="GLOSSARY-ROLE"><span class="glossterm">Role</span></dt><dd class="glossdef"><p>
+     A collection of access privileges to the
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">instance</a></em></a>.
+     Roles are themselves a privilege that can be granted to other roles.
+     This is often done for convenience or to ensure completeness
+     when multiple <a class="glossterm" href="glossary.html#GLOSSARY-USER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-USER" title="User">users</a></em></a> need
+     the same privileges.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createrole.html" title="CREATE ROLE"><span class="refentrytitle">CREATE ROLE</span></a>.
+    </p></dd><dt id="GLOSSARY-ROLLBACK"><span class="glossterm">Rollback</span></dt><dd class="glossdef"><p>
+     A command to undo all of the operations performed since the beginning
+     of a <a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION" title="Transaction">transaction</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-rollback.html" title="ROLLBACK"><span class="refentrytitle">ROLLBACK</span></a>.
+    </p></dd><dt id="GLOSSARY-ROUTINE"><span class="glossterm">Routine</span></dt><dd class="glossdef"><p>
+     A defined set of instructions stored in the database system
+     that can be invoked for execution.
+     A routine can be written in a variety of programming
+     languages.  Routines can be
+     <a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION" title="Function (routine)">functions</a></em></a>
+     (including set-returning functions and
+     <a class="glossterm" href="glossary.html#GLOSSARY-TRIGGER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TRIGGER" title="Trigger">trigger functions</a></em></a>),
+     <a class="glossterm" href="glossary.html#GLOSSARY-AGGREGATE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AGGREGATE" title="Aggregate function (routine)">aggregate functions</a></em></a>,
+     and <a class="glossterm" href="glossary.html#GLOSSARY-PROCEDURE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-PROCEDURE" title="Procedure (routine)">procedures</a></em></a>.
+    </p><p>
+     Many routines are already defined within <span class="productname">PostgreSQL</span>
+     itself, but user-defined ones can also be added.
+    </p></dd><dt><span class="glossterm">Row</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-TUPLE">Tuple</a>.</p></dd><dt id="GLOSSARY-SAVEPOINT"><span class="glossterm">Savepoint</span></dt><dd class="glossdef"><p>
+     A special mark in the sequence of steps in a
+     <a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION" title="Transaction">transaction</a></em></a>.
+     Data modifications after this point in time may be reverted
+     to the time of the savepoint.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-savepoint.html" title="SAVEPOINT"><span class="refentrytitle">SAVEPOINT</span></a>.
+    </p></dd><dt id="GLOSSARY-SCHEMA"><span class="glossterm">Schema</span></dt><dd class="glossdef"><p>
+     A schema is a namespace for
+     <a class="glossterm" href="glossary.html#GLOSSARY-SQL-OBJECT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SQL-OBJECT" title="SQL object">SQL objects</a></em></a>,
+     which all reside in the same
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a>.
+     Each SQL object must reside in exactly one schema.
+    </p><p>
+     All system-defined SQL objects reside in schema <code class="literal">pg_catalog</code>.
+    </p></dd><dd class="glossdef"><p>
+     More generically, the term <em class="firstterm">schema</em> is used to mean
+     all data descriptions (<a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a> definitions,
+     <a class="glossterm" href="glossary.html#GLOSSARY-CONSTRAINT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CONSTRAINT" title="Constraint">constraints</a></em></a>, comments, etc.)
+     for a given <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a> or
+     subset thereof.
+    </p><p>
+     For more information, see
+     <a class="xref" href="ddl-schemas.html" title="5.9. Schemas">Section 5.9</a>.
+    </p></dd><dt><span class="glossterm">Segment</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-FILE-SEGMENT">File segment</a>.</p></dd><dt id="GLOSSARY-SELECT"><span class="glossterm">Select</span></dt><dd class="glossdef"><p>
+     The <acronym class="acronym">SQL</acronym> command used to request data from a
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a>.
+     Normally, <code class="command">SELECT</code> commands are not expected to modify the
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a> in any way,
+     but it is possible that
+     <a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION" title="Function (routine)">functions</a></em></a> invoked within
+     the query could have side effects that do modify data.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-select.html" title="SELECT"><span class="refentrytitle">SELECT</span></a>.
+    </p></dd><dt id="GLOSSARY-SEQUENCE"><span class="glossterm">Sequence (relation)</span></dt><dd class="glossdef"><p>
+     A type of relation that is used to generate values.
+     Typically the generated values are sequential non-repeating numbers.
+     They are commonly used to generate surrogate
+     <a class="glossterm" href="glossary.html#GLOSSARY-PRIMARY-KEY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-PRIMARY-KEY" title="Primary key">primary key</a></em></a>
+     values.
+    </p></dd><dt id="GLOSSARY-SERVER"><span class="glossterm">Server</span></dt><dd class="glossdef"><p>
+     A computer on which <span class="productname">PostgreSQL</span>
+     <a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE" title="Instance">instances</a></em></a> run.
+     The term <em class="firstterm">server</em> denotes real hardware, a
+     container, or a <em class="firstterm">virtual machine</em>.
+    </p><p>
+     This term is sometimes used to refer to an instance or to a host.
+    </p></dd><dt id="GLOSSARY-SESSION"><span class="glossterm">Session</span></dt><dd class="glossdef"><p>
+     A state that allows a client and a backend to interact,
+     communicating over a <a class="glossterm" href="glossary.html#GLOSSARY-CONNECTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CONNECTION" title="Connection">connection</a></em></a>.
+    </p></dd><dt id="GLOSSARY-SHARED-MEMORY"><span class="glossterm">Shared memory</span></dt><dd class="glossdef"><p>
+     <acronym class="acronym">RAM</acronym> which is used by the processes common to an
+     <a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-INSTANCE" title="Instance">instance</a></em></a>.
+     It mirrors parts of <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a>
+     files, provides a transient area for
+     <a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECORD"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECORD" title="WAL record">WAL records</a></em></a>,
+     and stores additional common information.
+     Note that shared memory belongs to the complete instance, not to a single
+     database.
+    </p><p>
+     The largest part of shared memory is known as <em class="firstterm">shared buffers</em>
+     and is used to mirror part of data files, organized into pages.
+     When a page is modified, it is called a dirty page until it is
+     written back to the file system.
+    </p><p>
+     For more information, see
+     <a class="xref" href="runtime-config-resource.html#RUNTIME-CONFIG-RESOURCE-MEMORY" title="20.4.1. Memory">Section 20.4.1</a>.
+    </p></dd><dt id="GLOSSARY-SQL-OBJECT"><span class="glossterm">SQL object</span></dt><dd class="glossdef"><p>
+      Any object that can be created with a <code class="command">CREATE</code>
+      command.  Most objects are specific to one database, and are commonly
+      known as <em class="firstterm">local objects</em>.
+     </p><p>
+      Most local objects reside in a specific
+      <a class="glossterm" href="glossary.html#GLOSSARY-SCHEMA"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SCHEMA" title="Schema">schema</a></em></a> in their
+      containing database, such as
+      <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relations</a></em></a> (all types),
+      <a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION" title="Function (routine)">routines</a></em></a> (all types),
+      data types, etc.
+      The names of such objects of the same type in the same schema
+      are enforced to be unique.
+     </p><p>
+      There also exist local objects that do not reside in schemas; some examples are
+      <a class="glossterm" href="glossary.html#GLOSSARY-EXTENSION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-EXTENSION" title="Extension">extensions</a></em></a>,
+      <a class="glossterm" href="glossary.html#GLOSSARY-CAST"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CAST" title="Cast">data type casts</a></em></a>, and
+      <a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-DATA-WRAPPER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-DATA-WRAPPER" title="Foreign data wrapper">foreign data wrappers</a></em></a>.
+      The names of such objects of the same type are enforced to be unique
+      within the database.
+     </p><p>
+      Other object types, such as
+      <a class="glossterm" href="glossary.html#GLOSSARY-ROLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ROLE" title="Role">roles</a></em></a>,
+      <a class="glossterm" href="glossary.html#GLOSSARY-TABLESPACE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLESPACE" title="Tablespace">tablespaces</a></em></a>,
+      replication origins, subscriptions for logical replication, and
+      databases themselves are not local SQL objects since they exist
+      entirely outside of any specific database;
+      they are called <em class="firstterm">global objects</em>.
+      The names of such objects are enforced to be unique within the whole
+      database cluster.
+     </p><p>
+      For more information, see
+      <a class="xref" href="manage-ag-overview.html" title="23.1. Overview">Section 23.1</a>.
+    </p></dd><dt id="GLOSSARY-SQL-STANDARD"><span class="glossterm">SQL standard</span></dt><dd class="glossdef"><p>
+     A series of documents that define the <acronym class="acronym">SQL</acronym> language.
+    </p></dd><dt><span class="glossterm">Standby (server)</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-REPLICA">Replica (server)</a>.</p></dd><dt id="GLOSSARY-STARTUP-PROCESS"><span class="glossterm">Startup process</span></dt><dd class="glossdef"><p>
+     An <a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC" title="Auxiliary process">auxiliary process</a></em></a>
+     that replays WAL during crash recovery and in a
+     <a class="glossterm" href="glossary.html#GLOSSARY-REPLICATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-REPLICATION" title="Replication">physical replica</a></em></a>.
+    </p><p>
+     (The name is historical: the startup process was named before
+     replication was implemented; the name refers to its task as it
+     relates to the server startup following a crash.)
+    </p></dd><dt id="GLOSSARY-SYSTEM-CATALOG"><span class="glossterm">System catalog</span></dt><dd class="glossdef"><p>
+     A collection of <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">tables</a></em></a>
+     which describe the structure of all
+     <a class="glossterm" href="glossary.html#GLOSSARY-SQL-OBJECT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SQL-OBJECT" title="SQL object">SQL objects</a></em></a>
+     of the instance.
+     The system catalog resides in the schema <code class="literal">pg_catalog</code>.
+     These tables contain data in internal representation and are
+     not typically considered useful for user examination;
+     a number of user-friendlier <a class="glossterm" href="glossary.html#GLOSSARY-VIEW"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-VIEW" title="View">views</a></em></a>,
+     also in schema <code class="literal">pg_catalog</code>, offer more convenient access to
+     some of that information, while additional tables and views
+     exist in schema <code class="literal">information_schema</code>
+     (see <a class="xref" href="information-schema.html" title="Chapter 37. The Information Schema">Chapter 37</a>) that expose some
+     of the same and additional information as mandated by the
+     <a class="glossterm" href="glossary.html#GLOSSARY-SQL-STANDARD"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SQL-STANDARD" title="SQL standard">SQL standard</a></em></a>.
+    </p><p>
+      For more information, see
+      <a class="xref" href="ddl-schemas.html" title="5.9. Schemas">Section 5.9</a>.
+    </p></dd><dt id="GLOSSARY-TABLE"><span class="glossterm">Table</span></dt><dd class="glossdef"><p>
+     A collection of <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">tuples</a></em></a> having
+     a common data structure (the same number of
+     <a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE" title="Attribute">attributes</a></em></a>, in the same
+     order, having the same name and type per position).
+     A table is the most common form of
+     <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a> in
+     <span class="productname">PostgreSQL</span>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createtable.html" title="CREATE TABLE"><span class="refentrytitle">CREATE TABLE</span></a>.
+    </p></dd><dt id="GLOSSARY-TABLESPACE"><span class="glossterm">Tablespace</span></dt><dd class="glossdef"><p>
+     A named location on the server file system.
+     All <a class="glossterm" href="glossary.html#GLOSSARY-SQL-OBJECT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SQL-OBJECT" title="SQL object">SQL objects</a></em></a>
+     which require storage beyond their definition in the
+     <a class="glossterm" href="glossary.html#GLOSSARY-SYSTEM-CATALOG"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SYSTEM-CATALOG" title="System catalog">system catalog</a></em></a>
+     must belong to a single tablespace.
+     Initially, a database cluster contains a single usable tablespace which is
+     used as the default for all SQL objects, called <code class="literal">pg_default</code>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="manage-ag-tablespaces.html" title="23.6. Tablespaces">Section 23.6</a>.
+    </p></dd><dt id="GLOSSARY-TEMPORARY-TABLE"><span class="glossterm">Temporary table</span></dt><dd class="glossdef"><p>
+     <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">Tables</a></em></a> that exist either
+     for the lifetime of a
+     <a class="glossterm" href="glossary.html#GLOSSARY-SESSION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SESSION" title="Session">session</a></em></a> or a
+     <a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION" title="Transaction">transaction</a></em></a>, as
+     specified at the time of creation.
+     The data in them is not visible to other sessions, and is not
+     <a class="glossterm" href="glossary.html#GLOSSARY-LOGGED"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-LOGGED" title="Logged">logged</a></em></a>.
+     Temporary tables are often used to store intermediate data for a
+     multi-step operation.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createtable.html" title="CREATE TABLE"><span class="refentrytitle">CREATE TABLE</span></a>.
+    </p></dd><dt id="GLOSSARY-TOAST"><span class="glossterm">TOAST</span></dt><dd class="glossdef"><p>
+     A mechanism by which large attributes of table rows are split and
+     stored in a secondary table, called the <em class="firstterm">TOAST table</em>.
+     Each relation with large attributes has its own TOAST table.
+    </p><p>
+     For more information, see
+     <a class="xref" href="storage-toast.html" title="73.2. TOAST">Section 73.2</a>.
+    </p></dd><dt id="GLOSSARY-TRANSACTION"><span class="glossterm">Transaction</span></dt><dd class="glossdef"><p>
+     A combination of commands that must act as a single
+     <a class="glossterm" href="glossary.html#GLOSSARY-ATOMIC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ATOMIC" title="Atomic">atomic</a></em></a> command: they all
+     succeed or all fail as a single unit, and their effects are not visible to
+     other <a class="glossterm" href="glossary.html#GLOSSARY-SESSION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SESSION" title="Session">sessions</a></em></a> until
+     the transaction is complete, and possibly even later, depending on the
+     isolation level.
+    </p><p>
+     For more information, see
+     <a class="xref" href="transaction-iso.html" title="13.2. Transaction Isolation">Section 13.2</a>.
+    </p></dd><dt id="GLOSSARY-XID"><span class="glossterm">Transaction ID</span></dt><dd class="glossdef"><p>
+     The numerical, unique, sequentially-assigned identifier that each
+     transaction receives when it first causes a database modification.
+     Frequently abbreviated as <em class="firstterm">xid</em>.
+     When stored on disk, xids are only 32-bits wide, so only
+     approximately four billion write transaction IDs can be generated;
+     to permit the system to run for longer than that,
+     <em class="firstterm">epochs</em> are used, also 32 bits wide.
+     When the counter reaches the maximum xid value, it starts over at
+     <code class="literal">3</code> (values under that are reserved) and the
+     epoch value is incremented by one.
+     In some contexts, the epoch and xid values are
+     considered together as a single 64-bit value.
+    </p><p>
+     For more information, see
+     <a class="xref" href="datatype-oid.html" title="8.19. Object Identifier Types">Section 8.19</a>.
+    </p></dd><dt id="GLOSSARY-TPS"><span class="glossterm">Transactions per second (TPS)</span></dt><dd class="glossdef"><p>
+     Average number of transactions that are executed per second,
+     totaled across all sessions active for a measured run.
+     This is used as a measure of the performance characteristics of
+     an instance.
+    </p></dd><dt id="GLOSSARY-TRIGGER"><span class="glossterm">Trigger</span></dt><dd class="glossdef"><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION" title="Function (routine)">function</a></em></a> which can
+     be defined to execute whenever a certain operation (<code class="command">INSERT</code>,
+     <code class="command">UPDATE</code>, <code class="command">DELETE</code>,
+     <code class="command">TRUNCATE</code>) is applied to a
+     <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a>.
+     A trigger executes within the same
+     <a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TRANSACTION" title="Transaction">transaction</a></em></a> as the
+     statement which invoked it, and if the function fails, then the invoking
+     statement also fails.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createtrigger.html" title="CREATE TRIGGER"><span class="refentrytitle">CREATE TRIGGER</span></a>.
+    </p></dd><dt id="GLOSSARY-TUPLE"><span class="glossterm">Tuple</span></dt><dd class="glossdef"><p>
+     A collection of <a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ATTRIBUTE" title="Attribute">attributes</a></em></a>
+     in a fixed order.
+     That order may be defined by the <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a>
+     (or other <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a>)
+     where the tuple is contained, in which case the tuple is often called a
+     <em class="firstterm">row</em>.  It may also be defined by the structure of a
+     result set, in which case it is sometimes called a <em class="firstterm">record</em>.
+    </p></dd><dt id="GLOSSARY-UNIQUE-CONSTRAINT"><span class="glossterm">Unique constraint</span></dt><dd class="glossdef"><p>
+     A type of <a class="glossterm" href="glossary.html#GLOSSARY-CONSTRAINT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CONSTRAINT" title="Constraint">constraint</a></em></a>
+     defined on a <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a>
+     which restricts the values allowed in one or a combination of columns
+     so that each value or combination of values can only appear once in the
+     relation — that is, no other row in the relation contains values
+     that are equal to those.
+    </p><p>
+     Because <a class="glossterm" href="glossary.html#GLOSSARY-NULL"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-NULL" title="Null">null values</a></em></a> are
+     not considered equal to each other, multiple rows with null values are
+     allowed to exist without violating the unique constraint.
+    </p></dd><dt id="GLOSSARY-UNLOGGED"><span class="glossterm">Unlogged</span></dt><dd class="glossdef"><p>
+     The property of certain <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relations</a></em></a>
+     that the changes to them are not reflected in the
+     <a class="glossterm" href="glossary.html#GLOSSARY-WAL"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL" title="Write-ahead log">WAL</a></em></a>.
+     This disables replication and crash recovery for these relations.
+    </p><p>
+     The primary use of unlogged tables is for storing
+     transient work data that must be shared across processes.
+    </p><p>
+     <a class="glossterm" href="glossary.html#GLOSSARY-TEMPORARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TEMPORARY-TABLE" title="Temporary table">Temporary tables</a></em></a>
+     are always unlogged.
+    </p></dd><dt id="GLOSSARY-UPDATE"><span class="glossterm">Update</span></dt><dd class="glossdef"><p>
+     An <acronym class="acronym">SQL</acronym> command used to modify
+     <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">rows</a></em></a>
+     that may already exist in a specified <a class="glossterm" href="glossary.html#GLOSSARY-TABLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TABLE" title="Table">table</a></em></a>.
+     It cannot create or remove rows.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-update.html" title="UPDATE"><span class="refentrytitle">UPDATE</span></a>.
+    </p></dd><dt id="GLOSSARY-USER"><span class="glossterm">User</span></dt><dd class="glossdef"><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-ROLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-ROLE" title="Role">role</a></em></a> that has the
+     <code class="literal">LOGIN</code> privilege.
+    </p></dd><dt id="GLOSSARY-USER-MAPPING"><span class="glossterm">User mapping</span></dt><dd class="glossdef"><p>
+     The translation of login credentials in the local
+     <a class="glossterm" href="glossary.html#GLOSSARY-DATABASE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DATABASE" title="Database">database</a></em></a> to credentials
+     in a remote data system defined by a
+     <a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-DATA-WRAPPER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FOREIGN-DATA-WRAPPER" title="Foreign data wrapper">foreign data wrapper</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createusermapping.html" title="CREATE USER MAPPING"><span class="refentrytitle">CREATE USER MAPPING</span></a>.
+    </p></dd><dt id="GLOSSARY-VACUUM"><span class="glossterm">Vacuum</span></dt><dd class="glossdef"><p>
+     The process of removing outdated
+     <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">tuple versions</a></em></a>
+     from tables or materialized views, and other closely related
+     processing required by <span class="productname">PostgreSQL</span>'s
+     implementation of <a class="glossterm" href="glossary.html#GLOSSARY-MVCC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-MVCC" title="Multi-version concurrency control (MVCC)">MVCC</a></em></a>.
+     This can be initiated through the use of
+     the <code class="command">VACUUM</code> command, but can also be handled automatically
+     via <a class="glossterm" href="glossary.html#GLOSSARY-AUTOVACUUM"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AUTOVACUUM" title="Autovacuum (process)">autovacuum</a></em></a> processes.
+    </p><p>
+     For more information, see
+     <a class="xref" href="routine-vacuuming.html" title="25.1. Routine Vacuuming">Section 25.1</a> .
+    </p></dd><dt id="GLOSSARY-VIEW"><span class="glossterm">View</span></dt><dd class="glossdef"><p>
+     A <a class="glossterm" href="glossary.html#GLOSSARY-RELATION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RELATION" title="Relation">relation</a></em></a> that is defined by a
+     <code class="command">SELECT</code> statement, but has no storage of its own.
+     Any time a query references a view, the definition of the view is
+     substituted into the query as if the user had typed it as a subquery
+     instead of the name of the view.
+    </p><p>
+     For more information, see
+     <a class="xref" href="sql-createview.html" title="CREATE VIEW"><span class="refentrytitle">CREATE VIEW</span></a>.
+    </p></dd><dt id="GLOSSARY-VM"><span class="glossterm">Visibility map (fork)</span></dt><dd class="glossdef"><p>
+     A storage structure that keeps metadata about each data page
+     of a table's main fork.  The visibility map entry for
+     each page stores two bits: the first one
+     (<code class="literal">all-visible</code>) indicates that all tuples
+     in the page are visible to all transactions.  The second one
+     (<code class="literal">all-frozen</code>) indicates that all tuples
+     in the page are marked frozen.
+    </p></dd><dt><span class="glossterm">WAL</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-WAL">Write-ahead log</a>.</p></dd><dt id="GLOSSARY-WAL-ARCHIVER"><span class="glossterm">WAL archiver (process)</span></dt><dd class="glossdef"><p>
+     An <a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC" title="Auxiliary process">auxiliary process</a></em></a>
+     which, if enabled, saves copies of
+     <a class="glossterm" href="glossary.html#GLOSSARY-WAL-FILE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-FILE" title="WAL file">WAL files</a></em></a>
+     for the purpose of creating backups or keeping
+     <a class="glossterm" href="glossary.html#GLOSSARY-REPLICA"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-REPLICA" title="Replica (server)">replicas</a></em></a> current.
+    </p><p>
+     For more information, see
+     <a class="xref" href="continuous-archiving.html" title="26.3. Continuous Archiving and Point-in-Time Recovery (PITR)">Section 26.3</a>.
+    </p></dd><dt id="GLOSSARY-WAL-FILE"><span class="glossterm">WAL file</span></dt><dd class="glossdef"><p>
+     Also known as <em class="firstterm">WAL segment</em> or
+     <em class="firstterm">WAL segment file</em>.
+     Each of the sequentially-numbered files that provide storage space for
+     <a class="glossterm" href="glossary.html#GLOSSARY-WAL"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL" title="Write-ahead log">WAL</a></em></a>.
+     The files are all of the same predefined size
+     and are written in sequential order, interspersing changes
+     as they occur in multiple simultaneous sessions.
+     If the system crashes, the files are read in order, and each of the
+     changes is replayed to restore the system to the state it was in
+     before the crash.
+    </p><p>
+     Each WAL file can be released after a
+     <a class="glossterm" href="glossary.html#GLOSSARY-CHECKPOINT"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-CHECKPOINT" title="Checkpoint">checkpoint</a></em></a>
+     writes all the changes in it to the corresponding data files.
+     Releasing the file can be done either by deleting it, or by changing its
+     name so that it will be used in the future, which is called
+     <em class="firstterm">recycling</em>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="wal-internals.html" title="30.6. WAL Internals">Section 30.6</a>.
+    </p></dd><dt id="GLOSSARY-WAL-RECORD"><span class="glossterm">WAL record</span></dt><dd class="glossdef"><p>
+     A low-level description of an individual data change.
+     It contains sufficient information for the data change to be
+     re-executed (<em class="firstterm">replayed</em>) in case a system failure
+     causes the change to be lost.
+     WAL records use a non-printable binary format.
+    </p><p>
+     For more information, see
+     <a class="xref" href="wal-internals.html" title="30.6. WAL Internals">Section 30.6</a>.
+    </p></dd><dt id="GLOSSARY-WAL-RECEIVER"><span class="glossterm">WAL receiver (process)</span></dt><dd class="glossdef"><p>
+     An <a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AUXILIARY-PROC" title="Auxiliary process">auxiliary process</a></em></a>
+     that runs on a <a class="glossterm" href="glossary.html#GLOSSARY-REPLICA"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-REPLICA" title="Replica (server)">replica</a></em></a>
+     to receive WAL from the
+     <a class="glossterm" href="glossary.html#GLOSSARY-PRIMARY-SERVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-PRIMARY-SERVER" title="Primary (server)">primary server</a></em></a>
+     for replay by the
+     <a class="glossterm" href="glossary.html#GLOSSARY-STARTUP-PROCESS"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-STARTUP-PROCESS" title="Startup process">startup process</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="warm-standby.html" title="27.2. Log-Shipping Standby Servers">Section 27.2</a>.
+    </p></dd><dt><span class="glossterm">WAL segment</span></dt><dd><p>See <a class="glosssee" href="glossary.html#GLOSSARY-WAL-FILE">WAL file</a>.</p></dd><dt id="GLOSSARY-WAL-SENDER"><span class="glossterm">WAL sender (process)</span></dt><dd class="glossdef"><p>
+     A special <a class="glossterm" href="glossary.html#GLOSSARY-BACKEND"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-BACKEND" title="Backend (process)">backend process</a></em></a>
+     that streams WAL over a network.  The receiving end can be a
+     <a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECEIVER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECEIVER" title="WAL receiver (process)">WAL receiver</a></em></a>
+     in a <a class="glossterm" href="glossary.html#GLOSSARY-REPLICA"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-REPLICA" title="Replica (server)">replica</a></em></a>,
+     <a class="xref" href="app-pgreceivewal.html" title="pg_receivewal"><span class="refentrytitle"><span class="application">pg_receivewal</span></span></a>, or any other client program
+     that speaks the replication protocol.
+    </p></dd><dt id="GLOSSARY-WAL-WRITER"><span class="glossterm">WAL writer (process)</span></dt><dd class="glossdef"><p>
+     A process that writes <a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECORD"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECORD" title="WAL record">WAL records</a></em></a>
+     from <a class="glossterm" href="glossary.html#GLOSSARY-SHARED-MEMORY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-SHARED-MEMORY" title="Shared memory">shared memory</a></em></a> to
+     <a class="glossterm" href="glossary.html#GLOSSARY-WAL-FILE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-FILE" title="WAL file">WAL files</a></em></a>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="runtime-config-wal.html" title="20.5. Write Ahead Log">Section 20.5</a>.
+    </p></dd><dt id="GLOSSARY-WINDOW-FUNCTION"><span class="glossterm">Window function (routine)</span></dt><dd class="glossdef"><p>
+     A type of <a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-FUNCTION" title="Function (routine)">function</a></em></a>
+     used in a <a class="glossterm" href="glossary.html#GLOSSARY-QUERY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-QUERY" title="Query">query</a></em></a>
+     that applies to a <a class="glossterm" href="glossary.html#GLOSSARY-PARTITION"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-PARTITION" title="Partition">partition</a></em></a>
+     of the query's <a class="glossterm" href="glossary.html#GLOSSARY-RESULT-SET"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-RESULT-SET" title="Result set">result set</a></em></a>;
+     the function's result is based on values found in
+     <a class="glossterm" href="glossary.html#GLOSSARY-TUPLE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-TUPLE" title="Tuple">rows</a></em></a> of the same partition or frame.
+    </p><p>
+     All <a class="glossterm" href="glossary.html#GLOSSARY-AGGREGATE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-AGGREGATE" title="Aggregate function (routine)">aggregate functions</a></em></a>
+     can be used as window functions, but window functions can also be
+     used to, for example, give ranks to each of the rows in the partition.
+     Also known as <em class="firstterm">analytic functions</em>.
+    </p><p>
+     For more information, see
+     <a class="xref" href="tutorial-window.html" title="3.5. Window Functions">Section 3.5</a>.
+    </p></dd><dt id="GLOSSARY-WAL"><span class="glossterm">Write-ahead log</span></dt><dd class="glossdef"><p>
+     The journal that keeps track of the changes in the
+     <a class="glossterm" href="glossary.html#GLOSSARY-DB-CLUSTER"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-DB-CLUSTER" title="Database cluster">database cluster</a></em></a>
+     as user- and system-invoked operations take place.
+     It comprises many individual
+     <a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECORD"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-RECORD" title="WAL record">WAL records</a></em></a> written
+     sequentially to <a class="glossterm" href="glossary.html#GLOSSARY-WAL-FILE"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-WAL-FILE" title="WAL file">WAL files</a></em></a>.
+    </p></dd></dl></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="acronyms.html" title="Appendix L. Acronyms">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="appendixes.html" title="Part VIII. Appendixes">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="color.html" title="Appendix N. Color Support">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Appendix L. Acronyms </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> Appendix N. Color Support</td></tr></table></div></body></html>
+\ No newline at end of file
author	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-05-04 12:17:33 +0000
committer	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-05-04 12:17:33 +0000
commit	5e45211a64149b3c659b90ff2de6fa982a5a93ed (patch)
tree	739caf8c461053357daa9f162bef34516c7bf452 /doc/src/sgml/html/glossary.html
parent	Initial commit. (diff)
download	postgresql-15-5e45211a64149b3c659b90ff2de6fa982a5a93ed.tar.xz postgresql-15-5e45211a64149b3c659b90ff2de6fa982a5a93ed.zip