postgres/contrib/auto_explain/auto_explain.c

/*-------------------------------------------------------------------------
 *
 * auto_explain.c
 *
 *
 * Copyright (c) 2008-2017, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *	  contrib/auto_explain/auto_explain.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <limits.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_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_rate = 1;

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;

/* 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))

void		_PG_init(void);
void		_PG_fini(void);

static void explain_ExecutorStart(QueryDesc *queryDesc, int eflags);
static void explain_ExecutorRun(QueryDesc *queryDesc,
					ScanDirection direction,
					uint64 count, bool execute_once);
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);

	DefineCustomBoolVariable("auto_explain.log_triggers",
							 "Include trigger statistics in plans.",
						"This has no effect unless log_analyze is also set.",
							 &auto_explain_log_triggers,
							 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);

	DefineCustomRealVariable("auto_explain.sample_rate",
							 "Fraction of queries to process.",
							 NULL,
							 &auto_explain_sample_rate,
							 1.0,
							 0.0,
							 1.0,
							 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)
{
	/*
	 * For rate 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_rate *
								 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)
		{
			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() && current_query_sampled)
	{
		/*
		 * 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,
					uint64 count, bool execute_once)
{
	nesting_level++;
	PG_TRY();
	{
		if (prev_ExecutorRun)
			prev_ExecutorRun(queryDesc, direction, count, execute_once);
		else
			standard_ExecutorRun(queryDesc, direction, count, execute_once);
		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() && current_query_sampled)
	{
		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 = NewExplainState();

			es->analyze = (queryDesc->instrument_options && auto_explain_log_analyze);
			es->verbose = auto_explain_log_verbose;
			es->buffers = (es->analyze && auto_explain_log_buffers);
			es->timing = (es->analyze && auto_explain_log_timing);
			es->summary = es->analyze;
			es->format = auto_explain_log_format;

			ExplainBeginOutput(es);
			ExplainQueryText(es, queryDesc);
			ExplainPrintPlan(es, queryDesc);
			if (es->analyze && auto_explain_log_triggers)
				ExplainPrintTriggers(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';

			/* Fix JSON to output an object */
			if (auto_explain_log_format == EXPLAIN_FORMAT_JSON)
			{
				es->str->data[0] = '{';
				es->str->data[es->str->len - 1] = '}';
			}

			/*
			 * 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);
}