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3rd chunk of `doc/src/sgml/jit.sgml`
55a1fa0ca65211eb927250466902d23315316d7c823eb61b0000000100000b45
                   QUERY PLAN
-------------------------------------------------------------------&zwsp;------------------------------------------
 Aggregate  (cost=16.27..16.29 rows=1 width=8) (actual time=0.303..0.303 rows=1.00 loops=1)
   Buffers: shared hit=14
   ->  Seq Scan on pg_class  (cost=0.00..15.42 rows=342 width=4) (actual time=0.017..0.111 rows=356.00 loops=1)
         Buffers: shared hit=14
 Planning Time: 0.116 ms
 Execution Time: 0.365 ms
</screen>
   Given the cost of the plan, it is entirely reasonable that no
   <acronym>JIT</acronym> was used; the cost of <acronym>JIT</acronym> would
   have been bigger than the potential savings. Adjusting the cost limits
   will lead to <acronym>JIT</acronym> use:
<screen>
=# SET jit_above_cost = 10;
SET
=# EXPLAIN ANALYZE SELECT SUM(relpages) FROM pg_class;
                                                 QUERY PLAN
-------------------------------------------------------------------&zwsp;------------------------------------------
 Aggregate  (cost=16.27..16.29 rows=1 width=8) (actual time=6.049..6.049 rows=1.00 loops=1)
   Buffers: shared hit=14
   ->  Seq Scan on pg_class  (cost=0.00..15.42 rows=342 width=4) (actual time=0.019..0.052 rows=356.00 loops=1)
         Buffers: shared hit=14
 Planning Time: 0.133 ms
 JIT:
   Functions: 3
   Options: Inlining false, Optimization false, Expressions true, Deforming true
   Timing: Generation 1.259 ms (Deform 0.000 ms), Inlining 0.000 ms, Optimization 0.797 ms, Emission 5.048 ms, Total 7.104 ms
 Execution Time: 7.416 ms
</screen>
   As visible here, <acronym>JIT</acronym> was used, but inlining and
   expensive optimization were not. If <xref
   linkend="guc-jit-inline-above-cost"/> or <xref
   linkend="guc-jit-optimize-above-cost"/> were also lowered,
   that would change.
  </para>
 </sect1>

 <sect1 id="jit-configuration" xreflabel="JIT Configuration">
  <title>Configuration</title>

  <para>
   The configuration variable
   <xref linkend="guc-jit"/> determines whether <acronym>JIT</acronym>
   compilation is enabled or disabled.
   If it is enabled, the configuration variables
   <xref linkend="guc-jit-above-cost"/>, <xref
   linkend="guc-jit-inline-above-cost"/>, and <xref
   linkend="guc-jit-optimize-above-cost"/> determine
   whether <acronym>JIT</acronym> compilation is performed for a query,
   and how much effort is spent doing so.
  </para>

  <para>
   <xref linkend="guc-jit-provider"/> determines which <acronym>JIT</acronym>
   implementation is used. It is rarely required to be changed. See <xref
   linkend="jit-pluggable"/>.
  </para>

  <para>
   For development and debugging purposes a few additional configuration
   parameters exist, as described in
   <xref linkend="runtime-config-developer"/>.
  </para>
 </sect1>

 <sect1 id="jit-extensibility">
  <title>Extensibility</title>

  <sect2 id="jit-extensibility-bitcode">
Title: JIT Configuration and Query Execution in PostgreSQL
Summary
This section demonstrates how Just-in-Time (JIT) compilation affects query execution in PostgreSQL. It shows two EXPLAIN ANALYZE outputs for the same query. In the first case, JIT is not used due to the query cost being below the threshold. After lowering the jit_above_cost parameter to 10, JIT is applied in the second execution. The JIT-compiled query shows additional timing information for JIT functions, options, and phases. However, inlining and expensive optimizations were not performed in this case. The section also briefly mentions that further lowering of jit_inline_above_cost or jit_optimize_above_cost parameters could enable these additional optimizations.