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Allow setting sample ratio for auto_explain

New configuration parameter auto_explain.sample_ratio makes itpossible to log just a fraction of the queries meeting the configuredthreshold, to reduce the amount of logging.Author: Craig Ringer and Julien RouhaudReview: Petr Jelinek

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+46

-3

lines changed

contrib/auto_explain
- auto_explain.c
doc/src/sgml
- auto-explain.sgml

2 files changed

+46

-3

lines changed

`‎contrib/auto_explain/auto_explain.c‎`

Lines changed: 28 additions & 3 deletions

Original file line number	Diff line number	Diff line change
`@@ -29,6 +29,7 @@ static bool auto_explain_log_triggers = false;`
`29`	`29`	`staticboolauto_explain_log_timing= true;`
`30`	`30`	`staticintauto_explain_log_format=EXPLAIN_FORMAT_TEXT;`
`31`	`31`	`staticboolauto_explain_log_nested_statements= false;`
	`32`	`+staticdoubleauto_explain_sample_ratio=1;`
`32`	`33`
`33`	`34`	`staticconststructconfig_enum_entryformat_options[]= {`
`34`	`35`	`{"text",EXPLAIN_FORMAT_TEXT, false},`
`@@ -47,6 +48,9 @@ static ExecutorRun_hook_type prev_ExecutorRun = NULL;`
`47`	`48`	`staticExecutorFinish_hook_typeprev_ExecutorFinish=NULL;`
`48`	`49`	`staticExecutorEnd_hook_typeprev_ExecutorEnd=NULL;`
`49`	`50`
	`51`	`+/* Is the current query sampled, per backend */`
	`52`	`+staticboolcurrent_query_sampled= true;`
	`53`	`+`
`50`	`54`	`#defineauto_explain_enabled() \`
`51`	`55`	`(auto_explain_log_min_duration >= 0 && \`
`52`	`56`	`(nesting_level == 0 \|\| auto_explain_log_nested_statements))`
`@@ -159,6 +163,19 @@ _PG_init(void)`
`159`	`163`	`NULL,`
`160`	`164`	`NULL);`
`161`	`165`
	`166`	`+DefineCustomRealVariable("auto_explain.sample_ratio",`
	`167`	`+"Fraction of queries to process.",`
	`168`	`+NULL,`
	`169`	`+&auto_explain_sample_ratio,`
	`170`	`+1.0,`
	`171`	`+0.0,`
	`172`	`+1.0,`
	`173`	`+PGC_SUSET,`
	`174`	`+0,`
	`175`	`+NULL,`
	`176`	`+NULL,`
	`177`	`+NULL);`
	`178`	`+`
`162`	`179`	`EmitWarningsOnPlaceholders("auto_explain");`
`163`	`180`
`164`	`181`	`/* Install hooks. */`
`@@ -191,7 +208,15 @@ _PG_fini(void)`
`191`	`208`	`staticvoid`
`192`	`209`	`explain_ExecutorStart(QueryDesc*queryDesc,inteflags)`
`193`	`210`	`{`
`194`		`-if (auto_explain_enabled())`
	`211`	`+/*`
	`212`	`+ * For ratio sampling, randomly choose top-level statement. Either`
	`213`	`+ * all nested statements will be explained or none will.`
	`214`	`+ */`
	`215`	`+if (auto_explain_log_min_duration >=0&&nesting_level==0)`
	`216`	`+current_query_sampled= (random()<auto_explain_sample_ratio*`
	`217`	`+MAX_RANDOM_VALUE);`
	`218`	`+`
	`219`	`+if (auto_explain_enabled()&&current_query_sampled)`
`195`	`220`	`{`
`196`	`221`	`/* Enable per-node instrumentation iff log_analyze is required. */`
`197`	`222`	`if (auto_explain_log_analyze&& (eflags&EXEC_FLAG_EXPLAIN_ONLY)==0)`
`@@ -210,7 +235,7 @@ explain_ExecutorStart(QueryDesc *queryDesc, int eflags)`
`210`	`235`	`else`
`211`	`236`	`standard_ExecutorStart(queryDesc,eflags);`
`212`	`237`
`213`		`-if (auto_explain_enabled())`
	`238`	`+if (auto_explain_enabled()&&current_query_sampled)`
`214`	`239`	`{`
`215`	`240`	`/*`
`216`	`241`	`* Set up to track total elapsed time in ExecutorRun. Make sure the`
`@@ -280,7 +305,7 @@ explain_ExecutorFinish(QueryDesc *queryDesc)`
`280`	`305`	`staticvoid`
`281`	`306`	`explain_ExecutorEnd(QueryDesc*queryDesc)`
`282`	`307`	`{`
`283`		`-if (queryDesc->totaltime&&auto_explain_enabled())`
	`308`	`+if (queryDesc->totaltime&&auto_explain_enabled()&&current_query_sampled)`
`284`	`309`	`{`
`285`	`310`	`doublemsec;`
`286`	`311`

`‎doc/src/sgml/auto-explain.sgml‎`

Lines changed: 18 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -203,6 +203,24 @@ LOAD 'auto_explain';`
`203`	`203`	`</para>`
`204`	`204`	`</listitem>`
`205`	`205`	`</varlistentry>`
	`206`	`+`
	`207`	`+ <varlistentry>`
	`208`	`+ <term>`
	`209`	`+ <varname>auto_explain.sample_ratio</varname> (<type>real</type>)`
	`210`	`+ <indexterm>`
	`211`	`+ <primary><varname>auto_explain.sample_ratio</> configuration parameter</primary>`
	`212`	`+ </indexterm>`
	`213`	`+ </term>`
	`214`	`+ <listitem>`
	`215`	`+ <para>`
	`216`	`+ <varname>auto_explain.sample_ratio</varname> (<type>floating point</type>)`
	`217`	`+ causes auto_explain to only explain a fraction of the statements in each`
	`218`	`+ session. The default is 1, meaning explain all the queries. In case`
	`219`	`+ of nested statements, either all will be explained or none. Only`
	`220`	`+ superusers can change this setting.`
	`221`	`+ </para>`
	`222`	`+ </listitem>`
	`223`	`+ </varlistentry>`
`206`	`224`	`</variablelist>`
`207`	`225`
`208`	`226`	`<para>`

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Commit92f03fe

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`‎contrib/auto_explain/auto_explain.c‎`

`‎doc/src/sgml/auto-explain.sgml‎`

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