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Add EXPLAIN (MEMORY) to report planner memory consumption 

This adds a new "Memory:" line under the "Planning:" group (which
currently only has "Buffers:") when the MEMORY option is specified.

In order to make the reporting reasonably accurate, we create a separate
memory context for planner activities, to be used only when this option
is given.  The total amount of memory allocated by that context is
reported as "allocated"; we subtract memory in the context's freelists
from that and report that result as "used".  We use
MemoryContextStatsInternal() to obtain the quantities.

The code structure to show buffer usage during planning was not in
amazing shape, so I (Álvaro) modified the patch a bit to clean that up
in passing.

Author: Ashutosh Bapat
Reviewed-by: David Rowley, Andrey Lepikhov, Jian He, Andy Fan
Discussion: https://www.postgresql.org/message-id/CAExHW5sZA=5LJ_ZPpRO-w09ck8z9p7eaYAqq3Ks9GDfhrxeWBw@mail.gmail.com
This commit is contained in:
Alvaro Herrera 2024-01-29 17:53:03 +01:00
parent 6a1ea02c49
commit 5de890e361
No known key found for this signature in database
GPG Key ID: 1C20ACB9D5C564AE
9 changed files with 265 additions and 28 deletions
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2
contrib/auto_explain/auto_explain.c
View File

@ -396,6 +396,8 @@ explain_ExecutorEnd(QueryDesc *queryDesc)
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;

14
doc/src/sgml/ref/explain.sgml
View File

@ -44,6 +44,7 @@ EXPLAIN [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] <rep
WAL [ <replaceable class="parameter">boolean</replaceable> ]
TIMING [ <replaceable class="parameter">boolean</replaceable> ]
SUMMARY [ <replaceable class="parameter">boolean</replaceable> ]
MEMORY [ <replaceable class="parameter">boolean</replaceable> ]
FORMAT { TEXT | XML | JSON | YAML }
</synopsis>
</refsynopsisdiv>
@ -250,6 +251,19 @@ ROLLBACK;
</listitem>
</varlistentry>
<varlistentry>
<term><literal>MEMORY</literal></term>
<listitem>
<para>
Include information on memory consumption by the query planning phase.
Specifically, include the precise amount of storage used by planner
in-memory structures, as well as total memory considering allocation
overhead.
This parameter defaults to <literal>FALSE</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>FORMAT</literal></term>
<listitem>

152
src/backend/commands/explain.c
View File

@ -119,9 +119,11 @@ static void show_instrumentation_count(const char *qlabel, int which,
static void show_foreignscan_info(ForeignScanState *fsstate, ExplainState *es);
static void show_eval_params(Bitmapset *bms_params, ExplainState *es);
static const char *explain_get_index_name(Oid indexId);
static void show_buffer_usage(ExplainState *es, const BufferUsage *usage,
bool planning);
static bool peek_buffer_usage(ExplainState *es, const BufferUsage *usage);
static void show_buffer_usage(ExplainState *es, const BufferUsage *usage);
static void show_wal_usage(ExplainState *es, const WalUsage *usage);
static void show_memory_counters(ExplainState *es,
const MemoryContextCounters *mem_counters);
static void ExplainIndexScanDetails(Oid indexid, ScanDirection indexorderdir,
ExplainState *es);
static void ExplainScanTarget(Scan *plan, ExplainState *es);
@ -202,6 +204,8 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt,
summary_set = true;
es->summary = defGetBoolean(opt);
}
else if (strcmp(opt->defname, "memory") == 0)
es->memory = defGetBoolean(opt);
else if (strcmp(opt->defname, "format") == 0)
{
char *p = defGetString(opt);
@ -397,6 +401,25 @@ ExplainOneQuery(Query *query, int cursorOptions,
planduration;
BufferUsage bufusage_start,
bufusage;
MemoryContextCounters mem_counters;
MemoryContext planner_ctx = NULL;
MemoryContext saved_ctx = NULL;
if (es->memory)
{
/*
* Create a new memory context to measure planner's memory
* consumption accurately. Note that if the planner were to be
* modified to use a different memory context type, here we would
* be changing that to AllocSet, which might be undesirable.
* However, we don't have a way to create a context of the same
* type as another, so we pray and hope that this is OK.
*/
planner_ctx = AllocSetContextCreate(CurrentMemoryContext,
"explain analyze planner context",
ALLOCSET_DEFAULT_SIZES);
saved_ctx = MemoryContextSwitchTo(planner_ctx);
}
if (es->buffers)
bufusage_start = pgBufferUsage;
@ -408,6 +431,12 @@ ExplainOneQuery(Query *query, int cursorOptions,
INSTR_TIME_SET_CURRENT(planduration);
INSTR_TIME_SUBTRACT(planduration, planstart);
if (es->memory)
{
MemoryContextSwitchTo(saved_ctx);
MemoryContextMemConsumed(planner_ctx, &mem_counters);
}
/* calc differences of buffer counters. */
if (es->buffers)
{
@ -417,7 +446,8 @@ ExplainOneQuery(Query *query, int cursorOptions,
/* run it (if needed) and produce output */
ExplainOnePlan(plan, into, es, queryString, params, queryEnv,
&planduration, (es->buffers ? &bufusage : NULL));
&planduration, (es->buffers ? &bufusage : NULL),
es->memory ? &mem_counters : NULL);
}
}
@ -527,7 +557,8 @@ void
ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
const char *queryString, ParamListInfo params,
QueryEnvironment *queryEnv, const instr_time *planduration,
const BufferUsage *bufusage)
const BufferUsage *bufusage,
const MemoryContextCounters *mem_counters)
{
DestReceiver *dest;
QueryDesc *queryDesc;
@ -615,11 +646,27 @@ ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
/* Create textual dump of plan tree */
ExplainPrintPlan(es, queryDesc);
/* Show buffer usage in planning */
if (bufusage)
/* Show buffer and/or memory usage in planning */
if (peek_buffer_usage(es, bufusage) || mem_counters)
{
ExplainOpenGroup("Planning", "Planning", true, es);
show_buffer_usage(es, bufusage, true);
if (es->format == EXPLAIN_FORMAT_TEXT)
{
ExplainIndentText(es);
appendStringInfoString(es->str, "Planning:\n");
es->indent++;
}
if (bufusage)
show_buffer_usage(es, bufusage);
if (mem_counters)
show_memory_counters(es, mem_counters);
if (es->format == EXPLAIN_FORMAT_TEXT)
es->indent--;
ExplainCloseGroup("Planning", "Planning", true, es);
}
@ -2106,7 +2153,7 @@ ExplainNode(PlanState *planstate, List *ancestors,
/* Show buffer/WAL usage */
if (es->buffers && planstate->instrument)
show_buffer_usage(es, &planstate->instrument->bufusage, false);
show_buffer_usage(es, &planstate->instrument->bufusage);
if (es->wal && planstate->instrument)
show_wal_usage(es, &planstate->instrument->walusage);
@ -2125,7 +2172,7 @@ ExplainNode(PlanState *planstate, List *ancestors,
ExplainOpenWorker(n, es);
if (es->buffers)
show_buffer_usage(es, &instrument->bufusage, false);
show_buffer_usage(es, &instrument->bufusage);
if (es->wal)
show_wal_usage(es, &instrument->walusage);
ExplainCloseWorker(n, es);
@ -3545,10 +3592,52 @@ explain_get_index_name(Oid indexId)
}
/*
* Show buffer usage details.
* Return whether show_buffer_usage would have anything to print, if given
* the same 'usage' data. Note that when the format is anything other than
* text, we print even if the counters are all zeroes.
*/
static bool
peek_buffer_usage(ExplainState *es, const BufferUsage *usage)
{
bool has_shared;
bool has_local;
bool has_temp;
bool has_shared_timing;
bool has_local_timing;
bool has_temp_timing;
if (usage == NULL)
return false;
if (es->format != EXPLAIN_FORMAT_TEXT)
return true;
has_shared = (usage->shared_blks_hit > 0 ||
usage->shared_blks_read > 0 ||
usage->shared_blks_dirtied > 0 ||
usage->shared_blks_written > 0);
has_local = (usage->local_blks_hit > 0 ||
usage->local_blks_read > 0 ||
usage->local_blks_dirtied > 0 ||
usage->local_blks_written > 0);
has_temp = (usage->temp_blks_read > 0 ||
usage->temp_blks_written > 0);
has_shared_timing = (!INSTR_TIME_IS_ZERO(usage->shared_blk_read_time) ||
!INSTR_TIME_IS_ZERO(usage->shared_blk_write_time));
has_local_timing = (!INSTR_TIME_IS_ZERO(usage->local_blk_read_time) ||
!INSTR_TIME_IS_ZERO(usage->local_blk_write_time));
has_temp_timing = (!INSTR_TIME_IS_ZERO(usage->temp_blk_read_time) ||
!INSTR_TIME_IS_ZERO(usage->temp_blk_write_time));
return has_shared || has_local || has_temp || has_shared_timing ||
has_local_timing || has_temp_timing;
}
/*
* Show buffer usage details. This better be sync with peek_buffer_usage.
*/
static void
show_buffer_usage(ExplainState *es, const BufferUsage *usage, bool planning)
show_buffer_usage(ExplainState *es, const BufferUsage *usage)
{
if (es->format == EXPLAIN_FORMAT_TEXT)
{
@ -3568,18 +3657,6 @@ show_buffer_usage(ExplainState *es, const BufferUsage *usage, bool planning)
!INSTR_TIME_IS_ZERO(usage->local_blk_write_time));
bool has_temp_timing = (!INSTR_TIME_IS_ZERO(usage->temp_blk_read_time) ||
!INSTR_TIME_IS_ZERO(usage->temp_blk_write_time));
bool show_planning = (planning && (has_shared ||
has_local || has_temp ||
has_shared_timing ||
has_local_timing ||
has_temp_timing));
if (show_planning)
{
ExplainIndentText(es);
appendStringInfoString(es->str, "Planning:\n");
es->indent++;
}
/* Show only positive counter values. */
if (has_shared || has_local || has_temp)
@ -3678,9 +3755,6 @@ show_buffer_usage(ExplainState *es, const BufferUsage *usage, bool planning)
}
appendStringInfoChar(es->str, '\n');
}
if (show_planning)
es->indent--;
}
else
{
@ -3766,6 +3840,32 @@ show_wal_usage(ExplainState *es, const WalUsage *usage)
}
}
/*
* Show memory usage details.
*/
static void
show_memory_counters(ExplainState *es, const MemoryContextCounters *mem_counters)
{
if (es->format == EXPLAIN_FORMAT_TEXT)
{
ExplainIndentText(es);
appendStringInfo(es->str,
"Memory: used=%lld bytes allocated=%lld bytes",
(long long) (mem_counters->totalspace - mem_counters->freespace),
(long long) mem_counters->totalspace);
appendStringInfoChar(es->str, '\n');
}
else
{
ExplainPropertyInteger("Memory Used", "bytes",
mem_counters->totalspace - mem_counters->freespace,
es);
ExplainPropertyInteger("Memory Allocated", "bytes",
mem_counters->totalspace, es);
}
}
/*
* Add some additional details about an IndexScan or IndexOnlyScan
*/

22
src/backend/commands/prepare.c
View File

@ -583,6 +583,19 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into, ExplainState *es,
instr_time planduration;
BufferUsage bufusage_start,
bufusage;
MemoryContextCounters mem_counters;
MemoryContext planner_ctx = NULL;
MemoryContext saved_ctx = NULL;
if (es->memory)
{
/* See ExplainOneQuery about this */
Assert(IsA(CurrentMemoryContext, AllocSetContext));
planner_ctx = AllocSetContextCreate(CurrentMemoryContext,
"explain analyze planner context",
ALLOCSET_DEFAULT_SIZES);
saved_ctx = MemoryContextSwitchTo(planner_ctx);
}
if (es->buffers)
bufusage_start = pgBufferUsage;
@ -624,6 +637,12 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into, ExplainState *es,
INSTR_TIME_SET_CURRENT(planduration);
INSTR_TIME_SUBTRACT(planduration, planstart);
if (es->memory)
{
MemoryContextSwitchTo(saved_ctx);
MemoryContextMemConsumed(planner_ctx, &mem_counters);
}
/* calc differences of buffer counters. */
if (es->buffers)
{
@ -640,7 +659,8 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into, ExplainState *es,
if (pstmt->commandType != CMD_UTILITY)
ExplainOnePlan(pstmt, into, es, query_string, paramLI, queryEnv,
&planduration, (es->buffers ? &bufusage : NULL));
&planduration, (es->buffers ? &bufusage : NULL),
es->memory ? &mem_counters : NULL);
else
ExplainOneUtility(pstmt->utilityStmt, into, es, query_string,
paramLI, queryEnv);

13
src/backend/utils/mmgr/mcxt.c
View File

@ -687,6 +687,19 @@ MemoryContextMemAllocated(MemoryContext context, bool recurse)
return total;
}
/*
* Return the memory consumption statistics about the given context and its
* children.
*/
void
MemoryContextMemConsumed(MemoryContext context,
MemoryContextCounters *consumed)
{
memset(consumed, 0, sizeof(*consumed));
MemoryContextStatsInternal(context, 0, false, 0, consumed, false);
}
/*
* MemoryContextStats
* Print statistics about the named context and all its descendants.

4
src/include/commands/explain.h
View File

@ -45,6 +45,7 @@ typedef struct ExplainState
bool wal; /* print WAL usage */
bool timing; /* print detailed node timing */
bool summary; /* print total planning and execution timing */
bool memory; /* print planner's memory usage information */
bool settings; /* print modified settings */
bool generic; /* generate a generic plan */
ExplainFormat format; /* output format */
@ -92,7 +93,8 @@ extern void ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into,
ExplainState *es, const char *queryString,
ParamListInfo params, QueryEnvironment *queryEnv,
const instr_time *planduration,
const BufferUsage *bufusage);
const BufferUsage *bufusage,
const MemoryContextCounters *mem_counters);
extern void ExplainPrintPlan(ExplainState *es, QueryDesc *queryDesc);
extern void ExplainPrintTriggers(ExplainState *es, QueryDesc *queryDesc);

2
src/include/utils/memutils.h
View File

@ -84,6 +84,8 @@ extern Size GetMemoryChunkSpace(void *pointer);
extern MemoryContext MemoryContextGetParent(MemoryContext context);
extern bool MemoryContextIsEmpty(MemoryContext context);
extern Size MemoryContextMemAllocated(MemoryContext context, bool recurse);
extern void MemoryContextMemConsumed(MemoryContext context,
MemoryContextCounters *consumed);
extern void MemoryContextStats(MemoryContext context);
extern void MemoryContextStatsDetail(MemoryContext context, int max_children,
bool print_to_stderr);

76
src/test/regress/expected/explain.out
View File

@ -326,6 +326,82 @@ select explain_filter('explain (generic_plan) select unique1 from tenk1 where th
select explain_filter('explain (analyze, generic_plan) select unique1 from tenk1 where thousand = $1');
ERROR: EXPLAIN options ANALYZE and GENERIC_PLAN cannot be used together
CONTEXT: PL/pgSQL function explain_filter(text) line 5 at FOR over EXECUTE statement
-- MEMORY option
select explain_filter('explain (memory) select * from int8_tbl i8');
explain_filter
---------------------------------------------------------
Seq Scan on int8_tbl i8 (cost=N.N..N.N rows=N width=N)
Memory: used=N bytes allocated=N bytes
(2 rows)
select explain_filter('explain (memory, analyze) select * from int8_tbl i8');
explain_filter
-----------------------------------------------------------------------------------------------
Seq Scan on int8_tbl i8 (cost=N.N..N.N rows=N width=N) (actual time=N.N..N.N rows=N loops=N)
Memory: used=N bytes allocated=N bytes
Planning Time: N.N ms
Execution Time: N.N ms
(4 rows)
select explain_filter('explain (memory, summary, format yaml) select * from int8_tbl i8');
explain_filter
-------------------------------
- Plan: +
Node Type: "Seq Scan" +
Parallel Aware: false +
Async Capable: false +
Relation Name: "int8_tbl"+
Alias: "i8" +
Startup Cost: N.N +
Total Cost: N.N +
Plan Rows: N +
Plan Width: N +
Planning: +
Memory Used: N +
Memory Allocated: N +
Planning Time: N.N
(1 row)
select explain_filter('explain (memory, analyze, format json) select * from int8_tbl i8');
explain_filter
------------------------------------
[ +
{ +
"Plan": { +
"Node Type": "Seq Scan", +
"Parallel Aware": false, +
"Async Capable": false, +
"Relation Name": "int8_tbl",+
"Alias": "i8", +
"Startup Cost": N.N, +
"Total Cost": N.N, +
"Plan Rows": N, +
"Plan Width": N, +
"Actual Startup Time": N.N, +
"Actual Total Time": N.N, +
"Actual Rows": N, +
"Actual Loops": N +
}, +
"Planning": { +
"Memory Used": N, +
"Memory Allocated": N +
}, +
"Planning Time": N.N, +
"Triggers": [ +
], +
"Execution Time": N.N +
} +
]
(1 row)
prepare int8_query as select * from int8_tbl i8;
select explain_filter('explain (memory) execute int8_query');
explain_filter
---------------------------------------------------------
Seq Scan on int8_tbl i8 (cost=N.N..N.N rows=N width=N)
Memory: used=N bytes allocated=N bytes
(2 rows)
-- Test EXPLAIN (GENERIC_PLAN) with partition pruning
-- partitions should be pruned at plan time, based on constants,
-- but there should be no pruning based on parameter placeholders

8
src/test/regress/sql/explain.sql
View File

@ -94,6 +94,14 @@ select explain_filter('explain (generic_plan) select unique1 from tenk1 where th
-- should fail
select explain_filter('explain (analyze, generic_plan) select unique1 from tenk1 where thousand = $1');
-- MEMORY option
select explain_filter('explain (memory) select * from int8_tbl i8');
select explain_filter('explain (memory, analyze) select * from int8_tbl i8');
select explain_filter('explain (memory, summary, format yaml) select * from int8_tbl i8');
select explain_filter('explain (memory, analyze, format json) select * from int8_tbl i8');
prepare int8_query as select * from int8_tbl i8;
select explain_filter('explain (memory) execute int8_query');
-- Test EXPLAIN (GENERIC_PLAN) with partition pruning
-- partitions should be pruned at plan time, based on constants,
-- but there should be no pruning based on parameter placeholders