postgresql/contrib/auto_explain/auto_explain.c
Robert Haas af7914c662 Add TIMING option to EXPLAIN, to allow eliminating of timing overhead.
Sometimes it may be useful to get actual row counts out of EXPLAIN
(ANALYZE) without paying the cost of timing every node entry/exit.
With this patch, you can say EXPLAIN (ANALYZE, TIMING OFF) to get that.

Tomas Vondra, reviewed by Eric Theise, with minor doc changes by me.
2012-02-07 11:23:04 -05:00

322 lines
7.6 KiB
C

/*-------------------------------------------------------------------------
*
* auto_explain.c
*
*
* Copyright (c) 2008-2012, PostgreSQL Global Development Group
*
* IDENTIFICATION
* contrib/auto_explain/auto_explain.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "commands/explain.h"
#include "executor/instrument.h"
#include "utils/guc.h"
PG_MODULE_MAGIC;
/* GUC variables */
static int auto_explain_log_min_duration = -1; /* msec or -1 */
static bool auto_explain_log_analyze = false;
static bool auto_explain_log_verbose = false;
static bool auto_explain_log_buffers = false;
static bool auto_explain_log_timing = false;
static int auto_explain_log_format = EXPLAIN_FORMAT_TEXT;
static bool auto_explain_log_nested_statements = false;
static const struct config_enum_entry format_options[] = {
{"text", EXPLAIN_FORMAT_TEXT, false},
{"xml", EXPLAIN_FORMAT_XML, false},
{"json", EXPLAIN_FORMAT_JSON, false},
{"yaml", EXPLAIN_FORMAT_YAML, false},
{NULL, 0, false}
};
/* Current nesting depth of ExecutorRun calls */
static int nesting_level = 0;
/* Saved hook values in case of unload */
static ExecutorStart_hook_type prev_ExecutorStart = NULL;
static ExecutorRun_hook_type prev_ExecutorRun = NULL;
static ExecutorFinish_hook_type prev_ExecutorFinish = NULL;
static ExecutorEnd_hook_type prev_ExecutorEnd = NULL;
#define auto_explain_enabled() \
(auto_explain_log_min_duration >= 0 && \
(nesting_level == 0 || auto_explain_log_nested_statements))
void _PG_init(void);
void _PG_fini(void);
static void explain_ExecutorStart(QueryDesc *queryDesc, int eflags);
static void explain_ExecutorRun(QueryDesc *queryDesc,
ScanDirection direction,
long count);
static void explain_ExecutorFinish(QueryDesc *queryDesc);
static void explain_ExecutorEnd(QueryDesc *queryDesc);
/*
* Module load callback
*/
void
_PG_init(void)
{
/* Define custom GUC variables. */
DefineCustomIntVariable("auto_explain.log_min_duration",
"Sets the minimum execution time above which plans will be logged.",
"Zero prints all plans. -1 turns this feature off.",
&auto_explain_log_min_duration,
-1,
-1, INT_MAX / 1000,
PGC_SUSET,
GUC_UNIT_MS,
NULL,
NULL,
NULL);
DefineCustomBoolVariable("auto_explain.log_analyze",
"Use EXPLAIN ANALYZE for plan logging.",
NULL,
&auto_explain_log_analyze,
false,
PGC_SUSET,
0,
NULL,
NULL,
NULL);
DefineCustomBoolVariable("auto_explain.log_verbose",
"Use EXPLAIN VERBOSE for plan logging.",
NULL,
&auto_explain_log_verbose,
false,
PGC_SUSET,
0,
NULL,
NULL,
NULL);
DefineCustomBoolVariable("auto_explain.log_buffers",
"Log buffers usage.",
NULL,
&auto_explain_log_buffers,
false,
PGC_SUSET,
0,
NULL,
NULL,
NULL);
DefineCustomEnumVariable("auto_explain.log_format",
"EXPLAIN format to be used for plan logging.",
NULL,
&auto_explain_log_format,
EXPLAIN_FORMAT_TEXT,
format_options,
PGC_SUSET,
0,
NULL,
NULL,
NULL);
DefineCustomBoolVariable("auto_explain.log_nested_statements",
"Log nested statements.",
NULL,
&auto_explain_log_nested_statements,
false,
PGC_SUSET,
0,
NULL,
NULL,
NULL);
DefineCustomBoolVariable("auto_explain.log_timing",
"Collect timing data, not just row counts.",
NULL,
&auto_explain_log_timing,
true,
PGC_SUSET,
0,
NULL,
NULL,
NULL);
EmitWarningsOnPlaceholders("auto_explain");
/* Install hooks. */
prev_ExecutorStart = ExecutorStart_hook;
ExecutorStart_hook = explain_ExecutorStart;
prev_ExecutorRun = ExecutorRun_hook;
ExecutorRun_hook = explain_ExecutorRun;
prev_ExecutorFinish = ExecutorFinish_hook;
ExecutorFinish_hook = explain_ExecutorFinish;
prev_ExecutorEnd = ExecutorEnd_hook;
ExecutorEnd_hook = explain_ExecutorEnd;
}
/*
* Module unload callback
*/
void
_PG_fini(void)
{
/* Uninstall hooks. */
ExecutorStart_hook = prev_ExecutorStart;
ExecutorRun_hook = prev_ExecutorRun;
ExecutorFinish_hook = prev_ExecutorFinish;
ExecutorEnd_hook = prev_ExecutorEnd;
}
/*
* ExecutorStart hook: start up logging if needed
*/
static void
explain_ExecutorStart(QueryDesc *queryDesc, int eflags)
{
if (auto_explain_enabled())
{
/* Enable per-node instrumentation iff log_analyze is required. */
if (auto_explain_log_analyze && (eflags & EXEC_FLAG_EXPLAIN_ONLY) == 0)
{
if (auto_explain_log_timing)
queryDesc->instrument_options |= INSTRUMENT_TIMER;
else
queryDesc->instrument_options |= INSTRUMENT_ROWS;
if (auto_explain_log_buffers)
queryDesc->instrument_options |= INSTRUMENT_BUFFERS;
}
}
if (prev_ExecutorStart)
prev_ExecutorStart(queryDesc, eflags);
else
standard_ExecutorStart(queryDesc, eflags);
if (auto_explain_enabled())
{
/*
* Set up to track total elapsed time in ExecutorRun. Make sure the
* space is allocated in the per-query context so it will go away at
* ExecutorEnd.
*/
if (queryDesc->totaltime == NULL)
{
MemoryContext oldcxt;
oldcxt = MemoryContextSwitchTo(queryDesc->estate->es_query_cxt);
queryDesc->totaltime = InstrAlloc(1, INSTRUMENT_ALL);
MemoryContextSwitchTo(oldcxt);
}
}
}
/*
* ExecutorRun hook: all we need do is track nesting depth
*/
static void
explain_ExecutorRun(QueryDesc *queryDesc, ScanDirection direction, long count)
{
nesting_level++;
PG_TRY();
{
if (prev_ExecutorRun)
prev_ExecutorRun(queryDesc, direction, count);
else
standard_ExecutorRun(queryDesc, direction, count);
nesting_level--;
}
PG_CATCH();
{
nesting_level--;
PG_RE_THROW();
}
PG_END_TRY();
}
/*
* ExecutorFinish hook: all we need do is track nesting depth
*/
static void
explain_ExecutorFinish(QueryDesc *queryDesc)
{
nesting_level++;
PG_TRY();
{
if (prev_ExecutorFinish)
prev_ExecutorFinish(queryDesc);
else
standard_ExecutorFinish(queryDesc);
nesting_level--;
}
PG_CATCH();
{
nesting_level--;
PG_RE_THROW();
}
PG_END_TRY();
}
/*
* ExecutorEnd hook: log results if needed
*/
static void
explain_ExecutorEnd(QueryDesc *queryDesc)
{
if (queryDesc->totaltime && auto_explain_enabled())
{
double msec;
/*
* Make sure stats accumulation is done. (Note: it's okay if several
* levels of hook all do this.)
*/
InstrEndLoop(queryDesc->totaltime);
/* Log plan if duration is exceeded. */
msec = queryDesc->totaltime->total * 1000.0;
if (msec >= auto_explain_log_min_duration)
{
ExplainState es;
ExplainInitState(&es);
es.analyze = (queryDesc->instrument_options && auto_explain_log_analyze);
es.verbose = auto_explain_log_verbose;
es.buffers = (es.analyze && auto_explain_log_buffers);
es.format = auto_explain_log_format;
ExplainBeginOutput(&es);
ExplainQueryText(&es, queryDesc);
ExplainPrintPlan(&es, queryDesc);
ExplainEndOutput(&es);
/* Remove last line break */
if (es.str->len > 0 && es.str->data[es.str->len - 1] == '\n')
es.str->data[--es.str->len] = '\0';
/*
* Note: we rely on the existing logging of context or
* debug_query_string to identify just which statement is being
* reported. This isn't ideal but trying to do it here would
* often result in duplication.
*/
ereport(LOG,
(errmsg("duration: %.3f ms plan:\n%s",
msec, es.str->data),
errhidestmt(true)));
pfree(es.str->data);
}
}
if (prev_ExecutorEnd)
prev_ExecutorEnd(queryDesc);
else
standard_ExecutorEnd(queryDesc);
}