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Add EXPLAIN (MEMORY) to report planner memory consumption

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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
9 changed files with 265 additions and 28 deletions
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22
src/backend/commands/prepare.c
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@@ -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);