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1265a9c8f871cfa5aea4d607b1ab72b45b96dbb7
postgres/contrib/auto_explain/auto_explain.c
Tom Lane 5c0f7cc544 Fix ancient memory leak in contrib/auto_explain. 
The ExecutorEnd hook is invoked in a context that could be quite
long-lived, not the executor's own per-query context as I think
we were sort of assuming.  Thus, any cruft generated while producing
the EXPLAIN output could accumulate over multiple queries.  This can
result in spectacular leakage if log_nested_statements is on, and
even without that I'm surprised nobody complained before.

To fix, just switch into the executor's context so that anything we
allocate will be released when standard_ExecutorEnd frees the executor
state.  We might as well nuke the code's retail pfree of the explain
output string, too; that's laughably inadequate to the need.

Japin Li, per report from Jeff Janes.  This bug is old, so
back-patch to all supported branches.

Discussion: https://postgr.es/m/CAMkU=1wCVtbeRn0s9gt12KwQ7PLXovbpM8eg25SYocKW3BT4hg@mail.gmail.com
2021-02-02 13:49:08 -05:00

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/*-------------------------------------------------------------------------
*
* auto_explain.c
*
*
* Copyright (c) 2008-2021, 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 "executor/instrument.h"
#include "jit/jit.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_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 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;
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,
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_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);
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)
{
/*
* 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 = (random() < auto_explain_sample_rate *
((double) MAX_RANDOM_VALUE + 1));
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);
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);
}
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;
es->format = auto_explain_log_format;
es->settings = auto_explain_log_settings;
ExplainBeginOutput(es);
ExplainQueryText(es, queryDesc);
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);
}
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