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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-13 13:44:03 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-13 13:44:03 +0000
commit293913568e6a7a86fd1479e1cff8e2ecb58d6568 (patch)
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+<!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>32.1. What Is JIT compilation?</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="jit.html" title="Chapter 32. Just-in-Time Compilation (JIT)" /><link rel="next" href="jit-decision.html" title="32.2. When to JIT?" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">32.1. What Is <acronym class="acronym">JIT</acronym> compilation?</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="jit.html" title="Chapter 32. Just-in-Time Compilation (JIT)">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="jit.html" title="Chapter 32. Just-in-Time Compilation (JIT)">Up</a></td><th width="60%" align="center">Chapter 32. Just-in-Time Compilation (<acronym class="acronym">JIT</acronym>)</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="jit-decision.html" title="32.2. When to JIT?">Next</a></td></tr></table><hr /></div><div class="sect1" id="JIT-REASON"><div class="titlepage"><div><div><h2 class="title" style="clear: both">32.1. What Is <acronym class="acronym">JIT</acronym> compilation? <a href="#JIT-REASON" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="jit-reason.html#JIT-ACCELERATED-OPERATIONS">32.1.1. <acronym class="acronym">JIT</acronym> Accelerated Operations</a></span></dt><dt><span class="sect2"><a href="jit-reason.html#JIT-INLINING">32.1.2. Inlining</a></span></dt><dt><span class="sect2"><a href="jit-reason.html#JIT-OPTIMIZATION">32.1.3. Optimization</a></span></dt></dl></div><p>
+ Just-in-Time (<acronym class="acronym">JIT</acronym>) compilation is the process of turning
+ some form of interpreted program evaluation into a native program, and
+ doing so at run time.
+ For example, instead of using general-purpose code that can evaluate
+ arbitrary SQL expressions to evaluate a particular SQL predicate
+ like <code class="literal">WHERE a.col = 3</code>, it is possible to generate a
+ function that is specific to that expression and can be natively executed
+ by the CPU, yielding a speedup.
+ </p><p>
+ <span class="productname">PostgreSQL</span> has builtin support to perform
+ <acronym class="acronym">JIT</acronym> compilation using <a class="ulink" href="https://llvm.org/" target="_top"><span class="productname">LLVM</span></a> when
+ <span class="productname">PostgreSQL</span> is built with
+ <a class="link" href="install-make.html#CONFIGURE-WITH-LLVM"><code class="literal">--with-llvm</code></a>.
+ </p><p>
+ See <code class="filename">src/backend/jit/README</code> for further details.
+ </p><div class="sect2" id="JIT-ACCELERATED-OPERATIONS"><div class="titlepage"><div><div><h3 class="title">32.1.1. <acronym class="acronym">JIT</acronym> Accelerated Operations <a href="#JIT-ACCELERATED-OPERATIONS" class="id_link">#</a></h3></div></div></div><p>
+ Currently <span class="productname">PostgreSQL</span>'s <acronym class="acronym">JIT</acronym>
+ implementation has support for accelerating expression evaluation and
+ tuple deforming. Several other operations could be accelerated in the
+ future.
+ </p><p>
+ Expression evaluation is used to evaluate <code class="literal">WHERE</code>
+ clauses, target lists, aggregates and projections. It can be accelerated
+ by generating code specific to each case.
+ </p><p>
+ Tuple deforming is the process of transforming an on-disk tuple (see <a class="xref" href="storage-page-layout.html#STORAGE-TUPLE-LAYOUT" title="73.6.1. Table Row Layout">Section 73.6.1</a>) into its in-memory representation.
+ It can be accelerated by creating a function specific to the table layout
+ and the number of columns to be extracted.
+ </p></div><div class="sect2" id="JIT-INLINING"><div class="titlepage"><div><div><h3 class="title">32.1.2. Inlining <a href="#JIT-INLINING" class="id_link">#</a></h3></div></div></div><p>
+ <span class="productname">PostgreSQL</span> is very extensible and allows new
+ data types, functions, operators and other database objects to be defined;
+ see <a class="xref" href="extend.html" title="Chapter 38. Extending SQL">Chapter 38</a>. In fact the built-in objects are implemented
+ using nearly the same mechanisms. This extensibility implies some
+ overhead, for example due to function calls (see <a class="xref" href="xfunc.html" title="38.3. User-Defined Functions">Section 38.3</a>).
+ To reduce that overhead, <acronym class="acronym">JIT</acronym> compilation can inline the
+ bodies of small functions into the expressions using them. That allows a
+ significant percentage of the overhead to be optimized away.
+ </p></div><div class="sect2" id="JIT-OPTIMIZATION"><div class="titlepage"><div><div><h3 class="title">32.1.3. Optimization <a href="#JIT-OPTIMIZATION" class="id_link">#</a></h3></div></div></div><p>
+ <span class="productname">LLVM</span> has support for optimizing generated
+ code. Some of the optimizations are cheap enough to be performed whenever
+ <acronym class="acronym">JIT</acronym> is used, while others are only beneficial for
+ longer-running queries.
+ See <a class="ulink" href="https://llvm.org/docs/Passes.html#transform-passes" target="_top">https://llvm.org/docs/Passes.html#transform-passes</a> for
+ more details about optimizations.
+ </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="jit.html" title="Chapter 32. Just-in-Time Compilation (JIT)">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="jit.html" title="Chapter 32. Just-in-Time Compilation (JIT)">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="jit-decision.html" title="32.2. When to JIT?">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 32. Just-in-Time Compilation (<acronym class="acronym">JIT</acronym>) </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 32.2. When to <acronym class="acronym">JIT</acronym>?</td></tr></table></div></body></html> \ No newline at end of file
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