auto_explain.c

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/*-------------------------------------------------------------------------
 *
 * auto_explain.c
 *
 *
 * Copyright (c) 2008-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    contrib/auto_explain/auto_explain.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <limits.h>
 
#include "access/parallel.h"
#include "commands/explain.h"
#include "commands/explain_format.h"
#include "commands/explain_state.h"
#include "common/pg_prng.h"
#include "executor/instrument.h"
#include "utils/guc.h"
 
PG_MODULE_MAGIC_EXT(
                    .name = "auto_explain",
                    .version = PG_VERSION
);
 
/* GUC variables */
static int  auto_explain_log_min_duration = -1; /* msec or -1 */
static int  auto_explain_log_parameter_max_length = -1; /* bytes 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_wal = false;
static bool auto_explain_log_triggers = false;
static bool auto_explain_log_timing = true;
static bool auto_explain_log_settings = false;
static int  auto_explain_log_format = EXPLAIN_FORMAT_TEXT;
static int  auto_explain_log_level = LOG;
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}
};
 
static const struct config_enum_entry loglevel_options[] = {
    {"debug5", DEBUG5, false},
    {"debug4", DEBUG4, false},
    {"debug3", DEBUG3, false},
    {"debug2", DEBUG2, false},
    {"debug1", DEBUG1, false},
    {"debug", DEBUG2, true},
    {"info", INFO, false},
    {"notice", NOTICE, false},
    {"warning", WARNING, false},
    {"log", LOG, false},
    {NULL, 0, false}
};
 
/* Current nesting depth of ExecutorRun calls */
static int  nesting_level = 0;
 
/* Is the current top-level query to be sampled? */
static bool current_query_sampled = false;
 
#define auto_explain_enabled() \
    (auto_explain_log_min_duration >= 0 && \
     (nesting_level == 0 || auto_explain_log_nested_statements) && \
     current_query_sampled)
 
/* Saved hook values */
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;
 
static void explain_ExecutorStart(QueryDesc *queryDesc, int eflags);
static void explain_ExecutorRun(QueryDesc *queryDesc,
                                ScanDirection direction,
                                uint64 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.",
                            "-1 disables logging plans. 0 means log all plans.",
                            &auto_explain_log_min_duration,
                            -1,
                            -1, INT_MAX,
                            PGC_SUSET,
                            GUC_UNIT_MS,
                            NULL,
                            NULL,
                            NULL);
 
    DefineCustomIntVariable("auto_explain.log_parameter_max_length",
                            "Sets the maximum length of query parameter values to log.",
                            "-1 means log values in full.",
                            &auto_explain_log_parameter_max_length,
                            -1,
                            -1, INT_MAX,
                            PGC_SUSET,
                            GUC_UNIT_BYTE,
                            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_settings",
                             "Log modified configuration parameters affecting query planning.",
                             NULL,
                             &auto_explain_log_settings,
                             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_wal",
                             "Log WAL usage.",
                             NULL,
                             &auto_explain_log_wal,
                             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);
 
    DefineCustomEnumVariable("auto_explain.log_level",
                             "Log level for the plan.",
                             NULL,
                             &auto_explain_log_level,
                             LOG,
                             loglevel_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);
 
    MarkGUCPrefixReserved("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;
}
 
/*
 * ExecutorStart hook: start up logging if needed
 */
static void
explain_ExecutorStart(QueryDesc *queryDesc, int eflags)
{
    /*
     * At the beginning of each top-level statement, decide whether we'll
     * sample this statement.  If nested-statement explaining is enabled,
     * either all nested statements will be explained or none will.
     *
     * When in a parallel worker, we should do nothing, which we can implement
     * cheaply by pretending we decided not to sample the current statement.
     * If EXPLAIN is active in the parent session, data will be collected and
     * reported back to the parent, and it's no business of ours to interfere.
     */
    if (nesting_level == 0)
    {
        if (auto_explain_log_min_duration >= 0 && !IsParallelWorker())
            current_query_sampled = (pg_prng_double(&pg_global_prng_state) < auto_explain_sample_rate);
        else
            current_query_sampled = false;
    }
 
    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 (auto_explain_log_wal)
                queryDesc->instrument_options |= INSTRUMENT_WAL;
        }
    }
 
    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, false);
            MemoryContextSwitchTo(oldcxt);
        }
    }
}
 
/*
 * ExecutorRun hook: all we need do is track nesting depth
 */
static void
explain_ExecutorRun(QueryDesc *queryDesc, ScanDirection direction,
                    uint64 count)
{
    nesting_level++;
    PG_TRY();
    {
        if (prev_ExecutorRun)
            prev_ExecutorRun(queryDesc, direction, count);
        else
            standard_ExecutorRun(queryDesc, direction, count);
    }
    PG_FINALLY();
    {
        nesting_level--;
    }
    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);
    }
    PG_FINALLY();
    {
        nesting_level--;
    }
    PG_END_TRY();
}
 
/*
 * ExecutorEnd hook: log results if needed
 */
static void
explain_ExecutorEnd(QueryDesc *queryDesc)
{
    if (queryDesc->totaltime && auto_explain_enabled())
    {
        MemoryContext oldcxt;
        double      msec;
 
        /*
         * Make sure we operate in the per-query context, so any cruft will be
         * discarded later during ExecutorEnd.
         */
        oldcxt = MemoryContextSwitchTo(queryDesc->estate->es_query_cxt);
 
        /*
         * 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->wal = (es->analyze && auto_explain_log_wal);
            es->timing = (es->analyze && auto_explain_log_timing);
            es->summary = es->analyze;
            /* No support for MEMORY */
            /* es->memory = false; */
            es->format = auto_explain_log_format;
            es->settings = auto_explain_log_settings;
 
            ExplainBeginOutput(es);
            ExplainQueryText(es, queryDesc);
            ExplainQueryParameters(es, queryDesc->params, auto_explain_log_parameter_max_length);
            ExplainPrintPlan(es, queryDesc);
            if (es->analyze && auto_explain_log_triggers)
                ExplainPrintTriggers(es, queryDesc);
            if (es->costs)
                ExplainPrintJITSummary(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(auto_explain_log_level,
                    (errmsg("duration: %.3f ms  plan:\n%s",
                            msec, es->str->data),
                     errhidestmt(true)));
        }
 
        MemoryContextSwitchTo(oldcxt);
    }
 
    if (prev_ExecutorEnd)
        prev_ExecutorEnd(queryDesc);
    else
        standard_ExecutorEnd(queryDesc);
}