Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commit5de0cbd

Browse files
committed
Revert sampling patch for EXPLAIN ANALYZE; it turns out to be too unreliable
because node timing is much less predictable than the patch expects. I keptthe API change for InstrStopNode, however.
1 parent9143144 commit5de0cbd

File tree

3 files changed

+30
-179
lines changed

3 files changed

+30
-179
lines changed

‎src/backend/executor/execProcnode.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -12,7 +12,7 @@
1212
*
1313
*
1414
* IDENTIFICATION
15-
* $PostgreSQL: pgsql/src/backend/executor/execProcnode.c,v 1.55 2006/05/30 14:01:57 momjian Exp $
15+
* $PostgreSQL: pgsql/src/backend/executor/execProcnode.c,v 1.56 2006/06/09 19:30:56 tgl Exp $
1616
*
1717
*-------------------------------------------------------------------------
1818
*/
@@ -423,7 +423,7 @@ ExecProcNode(PlanState *node)
423423
}
424424

425425
if (node->instrument)
426-
InstrStopNode(node->instrument,TupIsNull(result) ?0 :1);
426+
InstrStopNode(node->instrument,TupIsNull(result) ?0.0 :1.0);
427427

428428
returnresult;
429429
}

‎src/backend/executor/instrument.c

Lines changed: 27 additions & 172 deletions
Original file line numberDiff line numberDiff line change
@@ -7,112 +7,22 @@
77
* Copyright (c) 2001-2006, PostgreSQL Global Development Group
88
*
99
* IDENTIFICATION
10-
* $PostgreSQL: pgsql/src/backend/executor/instrument.c,v 1.17 2006/06/07 18:49:03 tgl Exp $
10+
* $PostgreSQL: pgsql/src/backend/executor/instrument.c,v 1.18 2006/06/09 19:30:56 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
1414
#include"postgres.h"
1515

16-
#include<math.h>
1716
#include<unistd.h>
1817

1918
#include"executor/instrument.h"
2019

2120

22-
/*
23-
* As of PostgreSQL 8.2, we try to reduce the overhead of EXPLAIN ANALYZE
24-
* by not calling INSTR_TIME_SET_CURRENT() for every single node execution.
25-
* (Because that requires a kernel call on most systems, it's expensive.)
26-
*
27-
* This macro determines the sampling interval: that is, after how many more
28-
* iterations will we take the next time sample, given that niters iterations
29-
* have occurred already. In general, if the function is f(x), then for N
30-
* iterations we will take on the order of integral(1/f(x), x=0..N)
31-
* samples. Some examples follow, with the number of samples that would be
32-
* collected over 1,000,000 iterations:
33-
*
34-
*f(x) = x => log2(N) 20
35-
*f(x) = x^(1/2) => 2 * N^(1/2) 2000
36-
*f(x) = x^(1/3) => 1.5 * N^(2/3) 15000
37-
*
38-
* I've chosen the last one as it seems to provide a good compromise between
39-
* low overhead but still getting a meaningful number of samples. However,
40-
* not all machines have the cbrt() function so on those we substitute
41-
* sqrt(). The difference is not very significant in the tests I made.
42-
*
43-
* The actual sampling interval is randomized with the SampleFunc() value
44-
* as the mean; this hopefully will reduce any measurement bias due to
45-
* variation in the node execution time.
46-
*/
47-
#ifdefHAVE_CBRT
48-
#defineSampleFunc(niters) cbrt(niters)
49-
#else
50-
#defineSampleFunc(niters) sqrt(niters)
51-
#endif
52-
53-
#defineSampleInterval(niters) \
54-
(SampleFunc(niters) * (double) random() / (double) (MAX_RANDOM_VALUE/2))
55-
56-
/*
57-
* We sample at every node iteration until we've reached this threshold,
58-
* so that nodes not called a large number of times are completely accurate.
59-
* (Perhaps this should be a GUC variable?)
60-
*/
61-
#defineSAMPLE_THRESHOLD 50
62-
63-
/*
64-
* Determine the sampling overhead. This only needs to be done once per
65-
* backend (actually, probably once per postmaster would do ...)
66-
*/
67-
staticdoubleSampleOverhead;
68-
staticboolSampleOverheadCalculated= false;
69-
70-
staticvoid
71-
CalculateSampleOverhead(void)
72-
{
73-
inti;
74-
75-
/*
76-
* We could get a wrong result due to being interrupted by task switch.
77-
* To minimize the risk we do it a few times and take the lowest.
78-
*/
79-
SampleOverhead=1.0e6;
80-
81-
for (i=0;i<5;i++)
82-
{
83-
Instrumentationtimer;
84-
instr_timetmptime;
85-
intj;
86-
doubleoverhead;
87-
88-
memset(&timer,0,sizeof(timer));
89-
InstrStartNode(&timer);
90-
#defineTEST_COUNT 100
91-
for (j=0;j<TEST_COUNT;j++)
92-
{
93-
INSTR_TIME_SET_CURRENT(tmptime);
94-
}
95-
InstrStopNode(&timer,1);
96-
overhead=INSTR_TIME_GET_DOUBLE(timer.counter) /TEST_COUNT;
97-
if (overhead<SampleOverhead)
98-
SampleOverhead=overhead;
99-
}
100-
101-
SampleOverheadCalculated= true;
102-
}
103-
104-
10521
/* Allocate new instrumentation structure(s) */
10622
Instrumentation*
10723
InstrAlloc(intn)
10824
{
109-
Instrumentation*instr;
110-
111-
/* Calculate sampling overhead, if not done yet in this backend */
112-
if (!SampleOverheadCalculated)
113-
CalculateSampleOverhead();
114-
115-
instr=palloc0(n*sizeof(Instrumentation));
25+
Instrumentation*instr=palloc0(n*sizeof(Instrumentation));
11626

11727
/* we don't need to do any initialization except zero 'em */
11828

@@ -124,22 +34,7 @@ void
12434
InstrStartNode(Instrumentation*instr)
12535
{
12636
if (INSTR_TIME_IS_ZERO(instr->starttime))
127-
{
128-
/*
129-
* Always sample if not yet up to threshold, else check whether
130-
* next threshold has been reached
131-
*/
132-
if (instr->itercount<SAMPLE_THRESHOLD)
133-
instr->sampling= true;
134-
elseif (instr->itercount >=instr->nextsample)
135-
{
136-
instr->sampling= true;
137-
instr->nextsample=
138-
instr->itercount+SampleInterval(instr->itercount);
139-
}
140-
if (instr->sampling)
141-
INSTR_TIME_SET_CURRENT(instr->starttime);
142-
}
37+
INSTR_TIME_SET_CURRENT(instr->starttime);
14338
else
14439
elog(DEBUG2,"InstrStartNode called twice in a row");
14540
}
@@ -148,53 +43,39 @@ InstrStartNode(Instrumentation *instr)
14843
void
14944
InstrStopNode(Instrumentation*instr,doublenTuples)
15045
{
151-
/* count the returned tuples and iterations */
46+
instr_timeendtime;
47+
48+
/* count the returned tuples */
15249
instr->tuplecount+=nTuples;
153-
instr->itercount+=1;
15450

155-
/* measure runtime if appropriate */
156-
if (instr->sampling)
51+
if (INSTR_TIME_IS_ZERO(instr->starttime))
15752
{
158-
instr_timeendtime;
159-
160-
/*
161-
* To be sure that SampleOverhead accurately reflects the extra
162-
* overhead, we must do INSTR_TIME_SET_CURRENT() as the *first*
163-
* action that is different between the sampling and non-sampling
164-
* code paths.
165-
*/
166-
INSTR_TIME_SET_CURRENT(endtime);
53+
elog(DEBUG2,"InstrStopNode called without start");
54+
return;
55+
}
16756

168-
if (INSTR_TIME_IS_ZERO(instr->starttime))
169-
{
170-
elog(DEBUG2,"InstrStopNode called without start");
171-
return;
172-
}
57+
INSTR_TIME_SET_CURRENT(endtime);
17358

17459
#ifndefWIN32
175-
instr->counter.tv_sec+=endtime.tv_sec-instr->starttime.tv_sec;
176-
instr->counter.tv_usec+=endtime.tv_usec-instr->starttime.tv_usec;
60+
instr->counter.tv_sec+=endtime.tv_sec-instr->starttime.tv_sec;
61+
instr->counter.tv_usec+=endtime.tv_usec-instr->starttime.tv_usec;
17762

178-
/* Normalize after each add to avoid overflow/underflow of tv_usec */
179-
while (instr->counter.tv_usec<0)
180-
{
181-
instr->counter.tv_usec+=1000000;
182-
instr->counter.tv_sec--;
183-
}
184-
while (instr->counter.tv_usec >=1000000)
185-
{
186-
instr->counter.tv_usec-=1000000;
187-
instr->counter.tv_sec++;
188-
}
63+
/* Normalize after each add to avoid overflow/underflow of tv_usec */
64+
while (instr->counter.tv_usec<0)
65+
{
66+
instr->counter.tv_usec+=1000000;
67+
instr->counter.tv_sec--;
68+
}
69+
while (instr->counter.tv_usec >=1000000)
70+
{
71+
instr->counter.tv_usec-=1000000;
72+
instr->counter.tv_sec++;
73+
}
18974
#else/* WIN32 */
190-
instr->counter.QuadPart+= (endtime.QuadPart-instr->starttime.QuadPart);
75+
instr->counter.QuadPart+= (endtime.QuadPart-instr->starttime.QuadPart);
19176
#endif
19277

193-
INSTR_TIME_SET_ZERO(instr->starttime);
194-
195-
instr->samplecount+=1;
196-
instr->sampling= false;
197-
}
78+
INSTR_TIME_SET_ZERO(instr->starttime);
19879

19980
/* Is this the first tuple of this cycle? */
20081
if (!instr->running)
@@ -217,44 +98,18 @@ InstrEndLoop(Instrumentation *instr)
21798
if (!INSTR_TIME_IS_ZERO(instr->starttime))
21899
elog(DEBUG2,"InstrEndLoop called on running node");
219100

220-
/*Compute time spent in node */
101+
/*Accumulate per-cycle statistics into totals */
221102
totaltime=INSTR_TIME_GET_DOUBLE(instr->counter);
222103

223-
/*
224-
* If we didn't measure runtime on every iteration, then we must increase
225-
* the measured total to account for the other iterations. Naively
226-
* multiplying totaltime by itercount/samplecount would be wrong because
227-
* it effectively assumes the sampling overhead applies to all iterations,
228-
* even the ones we didn't measure. (Note that what we are trying to
229-
* estimate here is the actual time spent in the node, including the
230-
* actual measurement overhead; not the time exclusive of measurement
231-
* overhead.) We exclude the first iteration from the correction basis,
232-
* because it often takes longer than others.
233-
*/
234-
if (instr->itercount>instr->samplecount)
235-
{
236-
doubleper_iter;
237-
238-
per_iter= (totaltime-instr->firsttuple) / (instr->samplecount-1)
239-
-SampleOverhead;
240-
if (per_iter>0)/* sanity check */
241-
totaltime+=per_iter* (instr->itercount-instr->samplecount);
242-
}
243-
244-
/* Accumulate per-cycle statistics into totals */
245104
instr->startup+=instr->firsttuple;
246105
instr->total+=totaltime;
247106
instr->ntuples+=instr->tuplecount;
248107
instr->nloops+=1;
249108

250109
/* Reset for next cycle (if any) */
251110
instr->running= false;
252-
instr->sampling= false;
253111
INSTR_TIME_SET_ZERO(instr->starttime);
254112
INSTR_TIME_SET_ZERO(instr->counter);
255113
instr->firsttuple=0;
256114
instr->tuplecount=0;
257-
instr->itercount=0;
258-
instr->samplecount=0;
259-
instr->nextsample=0;
260115
}

‎src/include/executor/instrument.h

Lines changed: 1 addition & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -6,7 +6,7 @@
66
*
77
* Copyright (c) 2001-2006, PostgreSQL Global Development Group
88
*
9-
* $PostgreSQL: pgsql/src/include/executor/instrument.h,v 1.15 2006/05/30 19:24:25 tgl Exp $
9+
* $PostgreSQL: pgsql/src/include/executor/instrument.h,v 1.16 2006/06/09 19:30:56 tgl Exp $
1010
*
1111
*-------------------------------------------------------------------------
1212
*/
@@ -57,14 +57,10 @@ typedef struct Instrumentation
5757
{
5858
/* Info about current plan cycle: */
5959
boolrunning;/* TRUE if we've completed first tuple */
60-
boolsampling;/* Are we sampling in current iteration? */
6160
instr_timestarttime;/* Start time of current iteration of node */
6261
instr_timecounter;/* Accumulated runtime for this node */
6362
doublefirsttuple;/* Time for first tuple of this cycle */
6463
doubletuplecount;/* Tuples emitted so far this cycle */
65-
doubleitercount;/* Plan node iterations this cycle */
66-
doublesamplecount;/* Iterations in which we sampled runtime */
67-
doublenextsample;/* Next itercount to sample at */
6864
/* Accumulated statistics across all completed cycles: */
6965
doublestartup;/* Total startup time (in seconds) */
7066
doubletotal;/* Total total time (in seconds) */

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp