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The SQLITE_MEMSTAT Virtual Table
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<h1 id="overview"><span>1. </span>Overview</h1>
<p>
The SQLITE_MEMSTAT extension implements an <a href="vtab.html#epoonlyvtab">eponymous-only virtual table</a> that
provides SQL access to the <a href="c3ref/status.html">sqlite3_status64()</a> and
<a href="c3ref/db_status.html">sqlite3_db_status()</a> interfaces.
</p>
<p>
The SQLITE_STMT extension can also be loaded at run-time
by compiling the extension into a shared library or DLL using the source
code at <a href="https://sqlite.org/src/file/ext/misc/memstat.c">https://sqlite.org/src/file/ext/misc/memstat.c</a> and following the
instructions for how to <a href="loadext.html#build">compile loadable extensions</a>.
</p>
<h1 id="usage"><span>2. </span>Usage</h1>
<p>
The SQLITE_MEMSTAT virtual table is a read-only table that can be
queried to determine performance characteristics (primarily the
amount of memory being used) of the current instance of SQLite.
The SQLITE_MEMSTATE table is essentially a wrapper around the
C-language APIs <a href="c3ref/status.html">sqlite3_status64()</a> and <a href="c3ref/db_status.html">sqlite3_db_status()</a>.
If the
<a href="https://sqlite.org/src/file/ext/misc/memstat.c">memstat.c</a> source
file is compiled with the -DSQLITE_ENABLE_ZIPVFS option, then SQLITE_MEMSTAT
will also do some <a href="c3ref/file_control.html">file-control</a> calls to extract
memory usage information about the
<a href="https://www.hwaci.com/sw/sqlite/zipvfs.html">ZIPVFS</a> subsystem,
if that subsystem as been licensed, installed, and is in use.
</p><p>
The SQLITE_MEMSTAT table appears to have the following schema:
</p><div class="codeblock"><pre>CREATE TABLE sqlite_memstat(
name TEXT,
schema TEXT,
value INT,
hiwtr INT
);
</pre></div>
<p>
Each row of the SQLITE_MEMSTAT table corresponds to a single call to
one of the <a href="c3ref/status.html">sqlite3_status64()</a> or <a href="c3ref/db_status.html">sqlite3_db_status()</a> interfaces.
The NAME column of the row identifies which "verb" was passed to those
interfaces. For example, if <a href="c3ref/status.html">sqlite3_status64()</a> is invoked with
<a href="c3ref/c_status_malloc_count.html#sqlitestatusmemoryused">SQLITE_STATUS_MEMORY_USED</a>, then the NAME column is 'MEMORY_USED'.
Or if <a href="c3ref/db_status.html">sqlite3_db_status()</a> is invoked with <a href="c3ref/c_dbstatus_options.html#sqlitedbstatuscacheused">SQLITE_DBSTATUS_CACHE_USED</a>,
then the NAME column is "DB_CACHE_USED".
</p><p>
The SCHEMA column is NULL, except for cases when the <a href="c3ref/file_control.html">sqlite3_file_control()</a>
interface is used to interrogate the ZIPVFS backend. As this only happens
when the memstat.c module is compiled with -DSQLITE_ENABLE_ZIPVFS and when
<a href="https://www.hwaci.com/sw/sqlite/zipvfs.html">ZIPVFS</a> is in use,
SCHEMA is usually NULL.
</p><p>
The VALUE and HIWTR columns report the current value of the measure and
its "high-water mark". The high-water mark is the highest value ever seen
for the measurement, at least since the last reset. The SQLITE_MEMSTAT
virtual table does not provide a mechanism for resetting the high-water mark.
</p><p>
Depending on which parameter is being interrogated, one of the VALUE
or HIWTR mark measurements might be undefined. For example, only the
high-water mark is meaningful for <a href="c3ref/c_status_malloc_count.html#sqlitestatusmallocsize">SQLITE_STATUS_MALLOC_SIZE</a>, and
only the current value is meaningful for <a href="c3ref/c_dbstatus_options.html#sqlitedbstatuscacheused">SQLITE_DBSTATUS_CACHE_USED</a>.
For rows where one or the other of VALUE or HIWTR is not meaningful,
that value is returned as NULL.
the
interfaces, with the initial
</p><p align="center"><small><i>This page last modified on <a href="https://sqlite.org/docsrc/honeypot" id="mtimelink" data-href="https://sqlite.org/docsrc/finfo/pages/memstat.in?m=4d88e885eb1f60190">2018-09-28 23:43:25</a> UTC </small></i></p>
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