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Track I/O timing for temporary file blocks in EXPLAIN (BUFFERS)

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Previously, the output of EXPLAIN (BUFFERS) option showed only the I/O
timing spent reading and writing shared and local buffers.  This commit
adds on top of that the I/O timing for temporary buffers in the output
of EXPLAIN (for spilled external sorts, hashes, materialization. etc).
This can be helpful for users in cases where the I/O related to
temporary buffers is the bottleneck.

Like its cousin, this information is available only when track_io_timing
is enabled.  Playing the patch, this is showing an extra overhead of up
to 1% even when using gettimeofday() as implementation for interval
timings, which is slightly within the usual range noise still that's
measurable.

Author: Masahiko Sawada
Reviewed-by: Georgios Kokolatos, Melanie Plageman, Julien Rouhaud,
Ranier Vilela
Discussion: https://postgr.es/m/CAD21AoAJgotTeP83p6HiAGDhs_9Fw9pZ2J=_tYTsiO5Ob-V5GQ@mail.gmail.com
This commit is contained in:
Michael Paquier
2022-04-08 11:27:21 +09:00
parent dafae9707a
commit efb0ef909f
7 changed files with 147 additions and 68 deletions
Download Patch File Download Diff File Expand all files Collapse all files

42
src/backend/commands/explain.c
View File

@ -3521,8 +3521,11 @@ show_buffer_usage(ExplainState *es, const BufferUsage *usage, bool planning)
usage->temp_blks_written > 0);
bool has_timing = (!INSTR_TIME_IS_ZERO(usage->blk_read_time) ||
!INSTR_TIME_IS_ZERO(usage->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_timing));
has_local || has_temp || has_timing ||
has_temp_timing));
if (show_planning)
{
@ -3587,16 +3590,33 @@ show_buffer_usage(ExplainState *es, const BufferUsage *usage, bool planning)
}
/* As above, show only positive counter values. */
if (has_timing)
if (has_timing || has_temp_timing)
{
ExplainIndentText(es);
appendStringInfoString(es->str, "I/O Timings:");
if (!INSTR_TIME_IS_ZERO(usage->blk_read_time))
appendStringInfo(es->str, " read=%0.3f",
INSTR_TIME_GET_MILLISEC(usage->blk_read_time));
if (!INSTR_TIME_IS_ZERO(usage->blk_write_time))
appendStringInfo(es->str, " write=%0.3f",
INSTR_TIME_GET_MILLISEC(usage->blk_write_time));
if (has_timing)
{
appendStringInfoString(es->str, " shared/local");
if (!INSTR_TIME_IS_ZERO(usage->blk_read_time))
appendStringInfo(es->str, " read=%0.3f",
INSTR_TIME_GET_MILLISEC(usage->blk_read_time));
if (!INSTR_TIME_IS_ZERO(usage->blk_write_time))
appendStringInfo(es->str, " write=%0.3f",
INSTR_TIME_GET_MILLISEC(usage->blk_write_time));
if (has_temp_timing)
appendStringInfoChar(es->str, ',');
}
if (has_temp_timing)
{
appendStringInfoString(es->str, " temp");
if (!INSTR_TIME_IS_ZERO(usage->temp_blk_read_time))
appendStringInfo(es->str, " read=%0.3f",
INSTR_TIME_GET_MILLISEC(usage->temp_blk_read_time));
if (!INSTR_TIME_IS_ZERO(usage->temp_blk_write_time))
appendStringInfo(es->str, " write=%0.3f",
INSTR_TIME_GET_MILLISEC(usage->temp_blk_write_time));
}
appendStringInfoChar(es->str, '\n');
}
@ -3633,6 +3653,12 @@ show_buffer_usage(ExplainState *es, const BufferUsage *usage, bool planning)
ExplainPropertyFloat("I/O Write Time", "ms",
INSTR_TIME_GET_MILLISEC(usage->blk_write_time),
3, es);
ExplainPropertyFloat("Temp I/O Read Time", "ms",
INSTR_TIME_GET_MILLISEC(usage->temp_blk_read_time),
3, es);
ExplainPropertyFloat("Temp I/O Write Time", "ms",
INSTR_TIME_GET_MILLISEC(usage->temp_blk_write_time),
3, es);
}
}
}

6
src/backend/executor/instrument.c
View File

@ -237,6 +237,8 @@ BufferUsageAdd(BufferUsage *dst, const BufferUsage *add)
dst->temp_blks_written += add->temp_blks_written;
INSTR_TIME_ADD(dst->blk_read_time, add->blk_read_time);
INSTR_TIME_ADD(dst->blk_write_time, add->blk_write_time);
INSTR_TIME_ADD(dst->temp_blk_read_time, add->temp_blk_read_time);
INSTR_TIME_ADD(dst->temp_blk_write_time, add->temp_blk_write_time);
}
/* dst += add - sub */
@ -259,6 +261,10 @@ BufferUsageAccumDiff(BufferUsage *dst,
add->blk_read_time, sub->blk_read_time);
INSTR_TIME_ACCUM_DIFF(dst->blk_write_time,
add->blk_write_time, sub->blk_write_time);
INSTR_TIME_ACCUM_DIFF(dst->temp_blk_read_time,
add->temp_blk_read_time, sub->temp_blk_read_time);
INSTR_TIME_ACCUM_DIFF(dst->temp_blk_write_time,
add->temp_blk_write_time, sub->temp_blk_write_time);
}
/* helper functions for WAL usage accumulation */

29
src/backend/storage/file/buffile.c
View File

@ -429,6 +429,8 @@ static void
BufFileLoadBuffer(BufFile *file)
{
File thisfile;
instr_time io_start;
instr_time io_time;
/*
* Advance to next component file if necessary and possible.
@ -440,10 +442,14 @@ BufFileLoadBuffer(BufFile *file)
file->curOffset = 0L;
}
thisfile = file->files[file->curFile];
if (track_io_timing)
INSTR_TIME_SET_CURRENT(io_start);
/*
* Read whatever we can get, up to a full bufferload.
*/
thisfile = file->files[file->curFile];
file->nbytes = FileRead(thisfile,
file->buffer.data,
sizeof(file->buffer),
@ -458,6 +464,13 @@ BufFileLoadBuffer(BufFile *file)
FilePathName(thisfile))));
}
if (track_io_timing)
{
INSTR_TIME_SET_CURRENT(io_time);
INSTR_TIME_SUBTRACT(io_time, io_start);
INSTR_TIME_ADD(pgBufferUsage.temp_blk_read_time, io_time);
}
/* we choose not to advance curOffset here */
if (file->nbytes > 0)
@ -485,6 +498,8 @@ BufFileDumpBuffer(BufFile *file)
while (wpos < file->nbytes)
{
off_t availbytes;
instr_time io_start;
instr_time io_time;
/*
* Advance to next component file if necessary and possible.
@ -507,6 +522,10 @@ BufFileDumpBuffer(BufFile *file)
bytestowrite = (int) availbytes;
thisfile = file->files[file->curFile];
if (track_io_timing)
INSTR_TIME_SET_CURRENT(io_start);
bytestowrite = FileWrite(thisfile,
file->buffer.data + wpos,
bytestowrite,
@ -517,6 +536,14 @@ BufFileDumpBuffer(BufFile *file)
(errcode_for_file_access(),
errmsg("could not write to file \"%s\": %m",
FilePathName(thisfile))));
if (track_io_timing)
{
INSTR_TIME_SET_CURRENT(io_time);
INSTR_TIME_SUBTRACT(io_time, io_start);
INSTR_TIME_ADD(pgBufferUsage.temp_blk_write_time, io_time);
}
file->curOffset += bytestowrite;
wpos += bytestowrite;

6
src/include/executor/instrument.h
View File

@ -33,8 +33,10 @@ typedef struct BufferUsage
int64 local_blks_written; /* # of local disk blocks written */
int64 temp_blks_read; /* # of temp blocks read */
int64 temp_blks_written; /* # of temp blocks written */
instr_time blk_read_time; /* time spent reading */
instr_time blk_write_time; /* time spent writing */
instr_time blk_read_time; /* time spent reading blocks */
instr_time blk_write_time; /* time spent writing blocks */
instr_time temp_blk_read_time; /* time spent reading temp blocks */
instr_time temp_blk_write_time; /* time spent writing temp blocks */
} BufferUsage;
/*

112
src/test/regress/expected/explain.out
View File

@ -85,56 +85,6 @@ select explain_filter('explain (analyze, buffers, format text) select * from int
Execution Time: N.N ms
(3 rows)
select explain_filter('explain (analyze, buffers, 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, +
"Shared Hit Blocks": N, +
"Shared Read Blocks": N, +
"Shared Dirtied Blocks": N, +
"Shared Written Blocks": N, +
"Local Hit Blocks": N, +
"Local Read Blocks": N, +
"Local Dirtied Blocks": N, +
"Local Written Blocks": N, +
"Temp Read Blocks": N, +
"Temp Written Blocks": N +
}, +
"Planning": { +
"Shared Hit Blocks": N, +
"Shared Read Blocks": N, +
"Shared Dirtied Blocks": N, +
"Shared Written Blocks": N, +
"Local Hit Blocks": N, +
"Local Read Blocks": N, +
"Local Dirtied Blocks": N, +
"Local Written Blocks": N, +
"Temp Read Blocks": N, +
"Temp Written Blocks": N +
}, +
"Planning Time": N.N, +
"Triggers": [ +
], +
"Execution Time": N.N +
} +
]
(1 row)
select explain_filter('explain (analyze, buffers, format xml) select * from int8_tbl i8');
explain_filter
--------------------------------------------------------
@ -276,6 +226,68 @@ select explain_filter('explain (buffers, format json) select * from int8_tbl i8'
]
(1 row)
-- Check output including I/O timings. These fields are conditional
-- but always set in JSON format, so check them only in this case.
set track_io_timing = on;
select explain_filter('explain (analyze, buffers, 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, +
"Shared Hit Blocks": N, +
"Shared Read Blocks": N, +
"Shared Dirtied Blocks": N, +
"Shared Written Blocks": N, +
"Local Hit Blocks": N, +
"Local Read Blocks": N, +
"Local Dirtied Blocks": N, +
"Local Written Blocks": N, +
"Temp Read Blocks": N, +
"Temp Written Blocks": N, +
"I/O Read Time": N.N, +
"I/O Write Time": N.N, +
"Temp I/O Read Time": N.N, +
"Temp I/O Write Time": N.N +
}, +
"Planning": { +
"Shared Hit Blocks": N, +
"Shared Read Blocks": N, +
"Shared Dirtied Blocks": N, +
"Shared Written Blocks": N, +
"Local Hit Blocks": N, +
"Local Read Blocks": N, +
"Local Dirtied Blocks": N, +
"Local Written Blocks": N, +
"Temp Read Blocks": N, +
"Temp Written Blocks": N, +
"I/O Read Time": N.N, +
"I/O Write Time": N.N, +
"Temp I/O Read Time": N.N, +
"Temp I/O Write Time": N.N +
}, +
"Planning Time": N.N, +
"Triggers": [ +
], +
"Execution Time": N.N +
} +
]
(1 row)
set track_io_timing = off;
-- SETTINGS option
-- We have to ignore other settings that might be imposed by the environment,
-- so printing the whole Settings field unfortunately won't do.

7
src/test/regress/sql/explain.sql
View File

@ -65,12 +65,17 @@ select explain_filter('explain select * from int8_tbl i8');
select explain_filter('explain (analyze) select * from int8_tbl i8');
select explain_filter('explain (analyze, verbose) select * from int8_tbl i8');
select explain_filter('explain (analyze, buffers, format text) select * from int8_tbl i8');
select explain_filter('explain (analyze, buffers, format json) select * from int8_tbl i8');
select explain_filter('explain (analyze, buffers, format xml) select * from int8_tbl i8');
select explain_filter('explain (analyze, buffers, format yaml) select * from int8_tbl i8');
select explain_filter('explain (buffers, format text) select * from int8_tbl i8');
select explain_filter('explain (buffers, format json) select * from int8_tbl i8');
-- Check output including I/O timings. These fields are conditional
-- but always set in JSON format, so check them only in this case.
set track_io_timing = on;
select explain_filter('explain (analyze, buffers, format json) select * from int8_tbl i8');
set track_io_timing = off;
-- SETTINGS option
-- We have to ignore other settings that might be imposed by the environment,
-- so printing the whole Settings field unfortunately won't do.