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Allow setting sample ratio for auto_explain

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New configuration parameter auto_explain.sample_ratio makes it
possible to log just a fraction of the queries meeting the configured
threshold, to reduce the amount of logging.

Author: Craig Ringer and Julien Rouhaud
Review: Petr Jelinek
This commit is contained in:
Magnus Hagander
2016-03-11 15:08:34 +01:00
parent 69ab7b9d6c
commit 92f03fe76f
2 changed files with 46 additions and 3 deletions
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31
contrib/auto_explain/auto_explain.c
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@ -29,6 +29,7 @@ static bool auto_explain_log_triggers = false;
static bool auto_explain_log_timing = true;
static int auto_explain_log_format = EXPLAIN_FORMAT_TEXT;
static bool auto_explain_log_nested_statements = false;
static double auto_explain_sample_ratio = 1;
static const struct config_enum_entry format_options[] = {
{"text", EXPLAIN_FORMAT_TEXT, false},
@ -47,6 +48,9 @@ static ExecutorRun_hook_type prev_ExecutorRun = NULL;
static ExecutorFinish_hook_type prev_ExecutorFinish = NULL;
static ExecutorEnd_hook_type prev_ExecutorEnd = NULL;
/* Is the current query sampled, per backend */
static bool current_query_sampled = true;
#define auto_explain_enabled() \
(auto_explain_log_min_duration >= 0 && \
(nesting_level == 0 || auto_explain_log_nested_statements))
@ -159,6 +163,19 @@ _PG_init(void)
NULL,
NULL);
DefineCustomRealVariable("auto_explain.sample_ratio",
"Fraction of queries to process.",
NULL,
&auto_explain_sample_ratio,
1.0,
0.0,
1.0,
PGC_SUSET,
0,
NULL,
NULL,
NULL);
EmitWarningsOnPlaceholders("auto_explain");
/* Install hooks. */
@ -191,7 +208,15 @@ _PG_fini(void)
static void
explain_ExecutorStart(QueryDesc *queryDesc, int eflags)
{
if (auto_explain_enabled())
/*
* For ratio sampling, randomly choose top-level statement. Either
* all nested statements will be explained or none will.
*/
if (auto_explain_log_min_duration >= 0 && nesting_level == 0)
current_query_sampled = (random() < auto_explain_sample_ratio *
MAX_RANDOM_VALUE);
if (auto_explain_enabled() && current_query_sampled)
{
/* Enable per-node instrumentation iff log_analyze is required. */
if (auto_explain_log_analyze && (eflags & EXEC_FLAG_EXPLAIN_ONLY) == 0)
@ -210,7 +235,7 @@ explain_ExecutorStart(QueryDesc *queryDesc, int eflags)
else
standard_ExecutorStart(queryDesc, eflags);
if (auto_explain_enabled())
if (auto_explain_enabled() && current_query_sampled)
{
/*
* Set up to track total elapsed time in ExecutorRun. Make sure the
@ -280,7 +305,7 @@ explain_ExecutorFinish(QueryDesc *queryDesc)
static void
explain_ExecutorEnd(QueryDesc *queryDesc)
{
if (queryDesc->totaltime && auto_explain_enabled())
if (queryDesc->totaltime && auto_explain_enabled() && current_query_sampled)
{
double msec;