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Previously, it was unsafe to execute a plan in parallel if ExecutorRun() might be called with a non-zero row count. However, it's quite easy to fix things up so that we can support that case, provided that it is known that we will never call ExecutorRun() a second time for the same QueryDesc. Add infrastructure to signal this, and cross-checks to make sure that a caller who claims this is true doesn't later reneg. While that pattern never happens with queries received directly from a client -- there's no way to know whether multiple Execute messages will be sent unless the first one requests all the rows -- it's pretty common for queries originating from procedural languages, which often limit the result to a single tuple or to a user-specified number of tuples. This commit doesn't actually enable parallelism in any additional cases, because currently none of the places that would be able to benefit from this infrastructure pass CURSOR_OPT_PARALLEL_OK in the first place, but it makes it much more palatable to pass CURSOR_OPT_PARALLEL_OK in places where we currently don't, because it eliminates some cases where we'd end up having to run the parallel plan serially. Patch by me, based on some ideas from Rafia Sabih and corrected by Rafia Sabih based on feedback from Dilip Kumar and myself. Discussion: http://postgr.es/m/CA+TgmobXEhvHbJtWDuPZM9bVSLiTj-kShxQJ2uM5GPDze9fRYA@mail.gmail.com
370 lines
9.1 KiB
C
370 lines
9.1 KiB
C
/*-------------------------------------------------------------------------
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*
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* auto_explain.c
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*
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*
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* Copyright (c) 2008-2017, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* contrib/auto_explain/auto_explain.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include <limits.h>
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#include "commands/explain.h"
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#include "executor/instrument.h"
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#include "utils/guc.h"
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PG_MODULE_MAGIC;
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/* GUC variables */
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static int auto_explain_log_min_duration = -1; /* msec or -1 */
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static bool auto_explain_log_analyze = false;
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static bool auto_explain_log_verbose = false;
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static bool auto_explain_log_buffers = false;
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static bool auto_explain_log_triggers = false;
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static bool auto_explain_log_timing = true;
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static int auto_explain_log_format = EXPLAIN_FORMAT_TEXT;
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static bool auto_explain_log_nested_statements = false;
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static double auto_explain_sample_rate = 1;
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static const struct config_enum_entry format_options[] = {
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{"text", EXPLAIN_FORMAT_TEXT, false},
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{"xml", EXPLAIN_FORMAT_XML, false},
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{"json", EXPLAIN_FORMAT_JSON, false},
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{"yaml", EXPLAIN_FORMAT_YAML, false},
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{NULL, 0, false}
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};
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/* Current nesting depth of ExecutorRun calls */
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static int nesting_level = 0;
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/* Saved hook values in case of unload */
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static ExecutorStart_hook_type prev_ExecutorStart = NULL;
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static ExecutorRun_hook_type prev_ExecutorRun = NULL;
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static ExecutorFinish_hook_type prev_ExecutorFinish = NULL;
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static ExecutorEnd_hook_type prev_ExecutorEnd = NULL;
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/* Is the current query sampled, per backend */
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static bool current_query_sampled = true;
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#define auto_explain_enabled() \
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(auto_explain_log_min_duration >= 0 && \
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(nesting_level == 0 || auto_explain_log_nested_statements))
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void _PG_init(void);
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void _PG_fini(void);
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static void explain_ExecutorStart(QueryDesc *queryDesc, int eflags);
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static void explain_ExecutorRun(QueryDesc *queryDesc,
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ScanDirection direction,
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uint64 count, bool execute_once);
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static void explain_ExecutorFinish(QueryDesc *queryDesc);
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static void explain_ExecutorEnd(QueryDesc *queryDesc);
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/*
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* Module load callback
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*/
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void
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_PG_init(void)
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{
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/* Define custom GUC variables. */
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DefineCustomIntVariable("auto_explain.log_min_duration",
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"Sets the minimum execution time above which plans will be logged.",
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"Zero prints all plans. -1 turns this feature off.",
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&auto_explain_log_min_duration,
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-1,
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-1, INT_MAX / 1000,
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PGC_SUSET,
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GUC_UNIT_MS,
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NULL,
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NULL,
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NULL);
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DefineCustomBoolVariable("auto_explain.log_analyze",
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"Use EXPLAIN ANALYZE for plan logging.",
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NULL,
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&auto_explain_log_analyze,
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false,
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PGC_SUSET,
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0,
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NULL,
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NULL,
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NULL);
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DefineCustomBoolVariable("auto_explain.log_verbose",
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"Use EXPLAIN VERBOSE for plan logging.",
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NULL,
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&auto_explain_log_verbose,
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false,
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PGC_SUSET,
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0,
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NULL,
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NULL,
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NULL);
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DefineCustomBoolVariable("auto_explain.log_buffers",
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"Log buffers usage.",
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NULL,
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&auto_explain_log_buffers,
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false,
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PGC_SUSET,
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0,
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NULL,
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NULL,
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NULL);
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DefineCustomBoolVariable("auto_explain.log_triggers",
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"Include trigger statistics in plans.",
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"This has no effect unless log_analyze is also set.",
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&auto_explain_log_triggers,
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false,
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PGC_SUSET,
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0,
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NULL,
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NULL,
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NULL);
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DefineCustomEnumVariable("auto_explain.log_format",
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"EXPLAIN format to be used for plan logging.",
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NULL,
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&auto_explain_log_format,
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EXPLAIN_FORMAT_TEXT,
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format_options,
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PGC_SUSET,
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0,
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NULL,
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NULL,
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NULL);
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DefineCustomBoolVariable("auto_explain.log_nested_statements",
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"Log nested statements.",
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NULL,
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&auto_explain_log_nested_statements,
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false,
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PGC_SUSET,
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0,
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NULL,
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NULL,
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NULL);
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DefineCustomBoolVariable("auto_explain.log_timing",
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"Collect timing data, not just row counts.",
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NULL,
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&auto_explain_log_timing,
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true,
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PGC_SUSET,
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0,
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NULL,
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NULL,
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NULL);
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DefineCustomRealVariable("auto_explain.sample_rate",
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"Fraction of queries to process.",
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NULL,
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&auto_explain_sample_rate,
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1.0,
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0.0,
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1.0,
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PGC_SUSET,
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0,
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NULL,
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NULL,
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NULL);
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EmitWarningsOnPlaceholders("auto_explain");
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/* Install hooks. */
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prev_ExecutorStart = ExecutorStart_hook;
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ExecutorStart_hook = explain_ExecutorStart;
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prev_ExecutorRun = ExecutorRun_hook;
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ExecutorRun_hook = explain_ExecutorRun;
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prev_ExecutorFinish = ExecutorFinish_hook;
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ExecutorFinish_hook = explain_ExecutorFinish;
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prev_ExecutorEnd = ExecutorEnd_hook;
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ExecutorEnd_hook = explain_ExecutorEnd;
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}
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/*
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* Module unload callback
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*/
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void
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_PG_fini(void)
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{
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/* Uninstall hooks. */
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ExecutorStart_hook = prev_ExecutorStart;
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ExecutorRun_hook = prev_ExecutorRun;
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ExecutorFinish_hook = prev_ExecutorFinish;
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ExecutorEnd_hook = prev_ExecutorEnd;
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}
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/*
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* ExecutorStart hook: start up logging if needed
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*/
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static void
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explain_ExecutorStart(QueryDesc *queryDesc, int eflags)
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{
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/*
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* For rate sampling, randomly choose top-level statement. Either all
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* nested statements will be explained or none will.
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*/
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if (auto_explain_log_min_duration >= 0 && nesting_level == 0)
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current_query_sampled = (random() < auto_explain_sample_rate *
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MAX_RANDOM_VALUE);
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if (auto_explain_enabled() && current_query_sampled)
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{
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/* Enable per-node instrumentation iff log_analyze is required. */
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if (auto_explain_log_analyze && (eflags & EXEC_FLAG_EXPLAIN_ONLY) == 0)
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{
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if (auto_explain_log_timing)
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queryDesc->instrument_options |= INSTRUMENT_TIMER;
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else
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queryDesc->instrument_options |= INSTRUMENT_ROWS;
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if (auto_explain_log_buffers)
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queryDesc->instrument_options |= INSTRUMENT_BUFFERS;
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}
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}
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if (prev_ExecutorStart)
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prev_ExecutorStart(queryDesc, eflags);
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else
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standard_ExecutorStart(queryDesc, eflags);
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if (auto_explain_enabled() && current_query_sampled)
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{
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/*
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* Set up to track total elapsed time in ExecutorRun. Make sure the
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* space is allocated in the per-query context so it will go away at
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* ExecutorEnd.
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*/
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if (queryDesc->totaltime == NULL)
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{
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MemoryContext oldcxt;
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oldcxt = MemoryContextSwitchTo(queryDesc->estate->es_query_cxt);
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queryDesc->totaltime = InstrAlloc(1, INSTRUMENT_ALL);
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MemoryContextSwitchTo(oldcxt);
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}
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}
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}
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/*
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* ExecutorRun hook: all we need do is track nesting depth
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*/
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static void
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explain_ExecutorRun(QueryDesc *queryDesc, ScanDirection direction,
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uint64 count, bool execute_once)
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{
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nesting_level++;
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PG_TRY();
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{
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if (prev_ExecutorRun)
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prev_ExecutorRun(queryDesc, direction, count, execute_once);
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else
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standard_ExecutorRun(queryDesc, direction, count, execute_once);
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nesting_level--;
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}
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PG_CATCH();
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{
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nesting_level--;
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PG_RE_THROW();
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}
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PG_END_TRY();
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}
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/*
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* ExecutorFinish hook: all we need do is track nesting depth
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*/
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static void
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explain_ExecutorFinish(QueryDesc *queryDesc)
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{
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nesting_level++;
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PG_TRY();
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{
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if (prev_ExecutorFinish)
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prev_ExecutorFinish(queryDesc);
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else
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standard_ExecutorFinish(queryDesc);
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nesting_level--;
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}
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PG_CATCH();
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{
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nesting_level--;
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PG_RE_THROW();
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}
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PG_END_TRY();
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}
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/*
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* ExecutorEnd hook: log results if needed
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*/
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static void
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explain_ExecutorEnd(QueryDesc *queryDesc)
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{
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if (queryDesc->totaltime && auto_explain_enabled() && current_query_sampled)
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{
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double msec;
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/*
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* Make sure stats accumulation is done. (Note: it's okay if several
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* levels of hook all do this.)
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*/
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InstrEndLoop(queryDesc->totaltime);
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/* Log plan if duration is exceeded. */
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msec = queryDesc->totaltime->total * 1000.0;
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if (msec >= auto_explain_log_min_duration)
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{
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ExplainState *es = NewExplainState();
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es->analyze = (queryDesc->instrument_options && auto_explain_log_analyze);
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es->verbose = auto_explain_log_verbose;
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es->buffers = (es->analyze && auto_explain_log_buffers);
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es->timing = (es->analyze && auto_explain_log_timing);
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es->summary = es->analyze;
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es->format = auto_explain_log_format;
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ExplainBeginOutput(es);
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ExplainQueryText(es, queryDesc);
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ExplainPrintPlan(es, queryDesc);
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if (es->analyze && auto_explain_log_triggers)
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ExplainPrintTriggers(es, queryDesc);
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ExplainEndOutput(es);
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/* Remove last line break */
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if (es->str->len > 0 && es->str->data[es->str->len - 1] == '\n')
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es->str->data[--es->str->len] = '\0';
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/* Fix JSON to output an object */
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if (auto_explain_log_format == EXPLAIN_FORMAT_JSON)
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{
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es->str->data[0] = '{';
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es->str->data[es->str->len - 1] = '}';
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}
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/*
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* Note: we rely on the existing logging of context or
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* debug_query_string to identify just which statement is being
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* reported. This isn't ideal but trying to do it here would
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* often result in duplication.
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*/
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ereport(LOG,
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(errmsg("duration: %.3f ms plan:\n%s",
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msec, es->str->data),
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errhidestmt(true)));
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pfree(es->str->data);
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}
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}
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if (prev_ExecutorEnd)
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prev_ExecutorEnd(queryDesc);
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else
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standard_ExecutorEnd(queryDesc);
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}
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