diff options
Diffstat (limited to 'doc/src/sgml/html/mvcc-intro.html')
| -rw-r--r-- | doc/src/sgml/html/mvcc-intro.html | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/doc/src/sgml/html/mvcc-intro.html b/doc/src/sgml/html/mvcc-intro.html new file mode 100644 index 0000000..3e93497 --- /dev/null +++ b/doc/src/sgml/html/mvcc-intro.html @@ -0,0 +1,37 @@ +<?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>13.1. Introduction</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="mvcc.html" title="Chapter 13. Concurrency Control" /><link rel="next" href="transaction-iso.html" title="13.2. Transaction Isolation" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">13.1. Introduction</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="mvcc.html" title="Chapter 13. Concurrency Control">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="mvcc.html" title="Chapter 13. Concurrency Control">Up</a></td><th width="60%" align="center">Chapter 13. Concurrency Control</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 14.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="transaction-iso.html" title="13.2. Transaction Isolation">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="MVCC-INTRO"><div class="titlepage"><div><div><h2 class="title" style="clear: both">13.1. Introduction</h2></div></div></div><a id="id-1.5.12.4.2" class="indexterm"></a><a id="id-1.5.12.4.3" class="indexterm"></a><a id="id-1.5.12.4.4" class="indexterm"></a><a id="id-1.5.12.4.5" class="indexterm"></a><p> + <span class="productname">PostgreSQL</span> provides a rich set of tools + for developers to manage concurrent access to data. Internally, + data consistency is maintained by using a multiversion + model (Multiversion Concurrency Control, <acronym class="acronym">MVCC</acronym>). + This means that each SQL statement sees + a snapshot of data (a <em class="firstterm">database version</em>) + as it was some + time ago, regardless of the current state of the underlying data. + This prevents statements from viewing inconsistent data produced + by concurrent transactions performing updates on the same + data rows, providing <em class="firstterm">transaction isolation</em> + for each database session. <acronym class="acronym">MVCC</acronym>, by eschewing + the locking methodologies of traditional database systems, + minimizes lock contention in order to allow for reasonable + performance in multiuser environments. + </p><p> + The main advantage of using the <acronym class="acronym">MVCC</acronym> model of + concurrency control rather than locking is that in + <acronym class="acronym">MVCC</acronym> locks acquired for querying (reading) data + do not conflict with locks acquired for writing data, and so + reading never blocks writing and writing never blocks reading. + <span class="productname">PostgreSQL</span> maintains this guarantee + even when providing the strictest level of transaction + isolation through the use of an innovative <em class="firstterm">Serializable + Snapshot Isolation</em> (<acronym class="acronym">SSI</acronym>) level. + </p><p> + Table- and row-level locking facilities are also available in + <span class="productname">PostgreSQL</span> for applications which don't + generally need full transaction isolation and prefer to explicitly + manage particular points of conflict. However, proper + use of <acronym class="acronym">MVCC</acronym> will generally provide better + performance than locks. In addition, application-defined advisory + locks provide a mechanism for acquiring locks that are not tied + to a single transaction. + </p></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="mvcc.html" title="Chapter 13. Concurrency Control">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="mvcc.html" title="Chapter 13. Concurrency Control">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="transaction-iso.html" title="13.2. Transaction Isolation">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 13. Concurrency Control </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 14.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 13.2. Transaction Isolation</td></tr></table></div></body></html>
\ No newline at end of file |