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Add SETTINGS option to EXPLAIN, to print modified settings.
Query planning is affected by a number of configuration options, and it may be crucial to know which of those options were set to non-default values. With this patch you can say EXPLAIN (SETTINGS ON) to include that information in the query plan. Only options affecting planning, with values different from the built-in default are printed. This patch also adds auto_explain.log_settings option, providing the same capability in auto_explain module. Author: Tomas Vondra Reviewed-by: Rafia Sabih, John Naylor Discussion: https://postgr.es/m/e1791b4c-df9c-be02-edc5-7c8874944be0@2ndquadrant.com
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8 files changed

+333
-52
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8 files changed

+333
-52
lines changed

‎contrib/auto_explain/auto_explain.c

Lines changed: 13 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -28,6 +28,7 @@ static bool auto_explain_log_verbose = false;
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static bool auto_explain_log_buffers = false;
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static bool auto_explain_log_triggers = false;
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static bool auto_explain_log_timing = true;
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static bool auto_explain_log_settings = false;
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static int auto_explain_log_format = EXPLAIN_FORMAT_TEXT;
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static int auto_explain_log_level = LOG;
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static bool auto_explain_log_nested_statements = false;
@@ -112,6 +113,17 @@ _PG_init(void)
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NULL,
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NULL);
114115

116+
DefineCustomBoolVariable("auto_explain.log_settings",
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"Log modified configuration parameters affecting query planning.",
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NULL,
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&auto_explain_log_settings,
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false,
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PGC_SUSET,
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0,
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NULL,
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NULL,
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NULL);
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DefineCustomBoolVariable("auto_explain.log_verbose",
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"Use EXPLAIN VERBOSE for plan logging.",
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NULL,
@@ -356,6 +368,7 @@ explain_ExecutorEnd(QueryDesc *queryDesc)
356368
es->timing = (es->analyze && auto_explain_log_timing);
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es->summary = es->analyze;
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es->format = auto_explain_log_format;
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es->settings = auto_explain_log_settings;
359372

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ExplainBeginOutput(es);
361374
ExplainQueryText(es, queryDesc);

‎doc/src/sgml/auto-explain.sgml

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Original file line numberDiff line numberDiff line change
@@ -169,6 +169,24 @@ LOAD 'auto_explain';
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>auto_explain.log_settings</varname> (<type>boolean</type>)
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<indexterm>
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<primary><varname>auto_explain.log_settings</varname> configuration parameter</primary>
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</indexterm>
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</term>
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<listitem>
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<para>
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<varname>auto_explain.log_settings</varname> controls whether information
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about modified configuration options are printed when execution plan is logged.
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Only options affecting query planning with value different from the built-in
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default value are included in the output. This parameter is off by default.
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Only superusers can change this setting.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>auto_explain.log_format</varname> (<type>enum</type>)

‎doc/src/sgml/ref/explain.sgml

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Original file line numberDiff line numberDiff line change
@@ -39,6 +39,7 @@ EXPLAIN [ ANALYZE ] [ VERBOSE ] <replaceable class="parameter">statement</replac
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ANALYZE [ <replaceable class="parameter">boolean</replaceable> ]
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VERBOSE [ <replaceable class="parameter">boolean</replaceable> ]
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COSTS [ <replaceable class="parameter">boolean</replaceable> ]
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SETTINGS [ <replaceable class="parameter">boolean</replaceable> ]
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BUFFERS [ <replaceable class="parameter">boolean</replaceable> ]
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TIMING [ <replaceable class="parameter">boolean</replaceable> ]
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SUMMARY [ <replaceable class="parameter">boolean</replaceable> ]
@@ -152,6 +153,17 @@ ROLLBACK;
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>SETTINGS</literal></term>
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<listitem>
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<para>
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Include information on configuration parameters. Specifically, include
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options affecting query planning with value different from the built-in
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default value. This parameter defaults to <literal>FALSE</literal>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>BUFFERS</literal></term>
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<listitem>

‎src/backend/commands/explain.c

Lines changed: 76 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -29,6 +29,7 @@
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#include "storage/bufmgr.h"
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#include "tcop/tcopprot.h"
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#include "utils/builtins.h"
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#include "utils/guc_tables.h"
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#include "utils/json.h"
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#include "utils/lsyscache.h"
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#include "utils/rel.h"
@@ -162,6 +163,8 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt, const char *queryString,
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es->costs = defGetBoolean(opt);
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else if (strcmp(opt->defname, "buffers") == 0)
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es->buffers = defGetBoolean(opt);
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else if (strcmp(opt->defname, "settings") == 0)
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es->settings = defGetBoolean(opt);
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else if (strcmp(opt->defname, "timing") == 0)
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{
167170
timing_set = true;
@@ -596,6 +599,73 @@ ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
596599
ExplainCloseGroup("Query", NULL, true, es);
597600
}
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602+
/*
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* ExplainPrintSettings -
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* Print summary of modified settings affecting query planning.
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*/
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static void
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ExplainPrintSettings(ExplainState *es)
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{
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int num;
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struct config_generic **gucs;
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/* bail out if information about settings not requested */
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if (!es->settings)
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return;
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/* request an array of relevant settings */
617+
gucs = get_explain_guc_options(&num);
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/* also bail out of there are no options */
620+
if (!num)
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return;
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623+
if (es->format != EXPLAIN_FORMAT_TEXT)
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{
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int i;
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ExplainOpenGroup("Settings", "Settings", true, es);
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629+
for (i = 0; i < num; i++)
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{
631+
char *setting;
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struct config_generic *conf = gucs[i];
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setting = GetConfigOptionByName(conf->name, NULL, true);
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ExplainPropertyText(conf->name, setting, es);
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}
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ExplainCloseGroup("Settings", "Settings", true, es);
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}
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else
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{
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int i;
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StringInfoData str;
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initStringInfo(&str);
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for (i = 0; i < num; i++)
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{
650+
char *setting;
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struct config_generic *conf = gucs[i];
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if (i > 0)
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appendStringInfoString(&str, ", ");
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setting = GetConfigOptionByName(conf->name, NULL, true);
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if (setting)
659+
appendStringInfo(&str, "%s = '%s'", conf->name, setting);
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else
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appendStringInfo(&str, "%s = NULL", conf->name);
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}
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664+
if (num > 0)
665+
ExplainPropertyText("Settings", str.data, es);
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}
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}
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599669
/*
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* ExplainPrintPlan -
601671
* convert a QueryDesc's plan tree to text and append it to es->str
@@ -633,6 +703,12 @@ ExplainPrintPlan(ExplainState *es, QueryDesc *queryDesc)
633703
if (IsA(ps, GatherState) &&((Gather *) ps->plan)->invisible)
634704
ps = outerPlanState(ps);
635705
ExplainNode(ps, NIL, NULL, NULL, es);
706+
707+
/*
708+
* If requested, include information about GUC parameters with values
709+
* that don't match the built-in defaults.
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*/
711+
ExplainPrintSettings(es);
636712
}
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/*

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