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Commitd2a4a40

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Add a line to the EXPLAIN ANALYZE output for a Sort node, showing the
actual sort strategy and amount of space used. By popular demand.
1 parentc746472 commitd2a4a40

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3 files changed

+94
-3
lines changed

3 files changed

+94
-3
lines changed

‎src/backend/commands/explain.c

Lines changed: 28 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1994-5, Regents of the University of California
88
*
99
* IDENTIFICATION
10-
* $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.162 2007/04/27 22:05:47 tgl Exp $
10+
* $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.163 2007/05/04 21:29:52 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -30,6 +30,7 @@
3030
#include"utils/builtins.h"
3131
#include"utils/guc.h"
3232
#include"utils/lsyscache.h"
33+
#include"utils/tuplesort.h"
3334

3435

3536
typedefstructExplainState
@@ -58,6 +59,8 @@ static void show_upper_qual(List *qual, const char *qlabel, Plan *plan,
5859
staticvoidshow_sort_keys(Plan*sortplan,intnkeys,AttrNumber*keycols,
5960
constchar*qlabel,
6061
StringInfostr,intindent,ExplainState*es);
62+
staticvoidshow_sort_info(SortState*sortstate,
63+
StringInfostr,intindent,ExplainState*es);
6164

6265
/*
6366
* ExplainQuery -
@@ -818,6 +821,8 @@ explain_outNode(StringInfo str,
818821
((Sort*)plan)->sortColIdx,
819822
"Sort Key",
820823
str,indent,es);
824+
show_sort_info((SortState*)planstate,
825+
str,indent,es);
821826
break;
822827
caseT_Result:
823828
show_upper_qual((List*) ((Result*)plan)->resconstantqual,
@@ -1123,3 +1128,25 @@ show_sort_keys(Plan *sortplan, int nkeys, AttrNumber *keycols,
11231128

11241129
appendStringInfo(str,"\n");
11251130
}
1131+
1132+
/*
1133+
* If it's EXPLAIN ANALYZE, show tuplesort explain info for a sort node
1134+
*/
1135+
staticvoid
1136+
show_sort_info(SortState*sortstate,
1137+
StringInfostr,intindent,ExplainState*es)
1138+
{
1139+
Assert(IsA(sortstate,SortState));
1140+
if (es->printAnalyze&&sortstate->sort_Done&&
1141+
sortstate->tuplesortstate!=NULL)
1142+
{
1143+
char*sortinfo;
1144+
inti;
1145+
1146+
sortinfo=tuplesort_explain((Tuplesortstate*)sortstate->tuplesortstate);
1147+
for (i=0;i<indent;i++)
1148+
appendStringInfo(str," ");
1149+
appendStringInfo(str," %s\n",sortinfo);
1150+
pfree(sortinfo);
1151+
}
1152+
}

‎src/backend/utils/sort/tuplesort.c

Lines changed: 63 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -91,7 +91,7 @@
9191
* Portions Copyright (c) 1994, Regents of the University of California
9292
*
9393
* IDENTIFICATION
94-
* $PostgreSQL: pgsql/src/backend/utils/sort/tuplesort.c,v 1.75 2007/05/0401:13:44 tgl Exp $
94+
* $PostgreSQL: pgsql/src/backend/utils/sort/tuplesort.c,v 1.76 2007/05/0421:29:53 tgl Exp $
9595
*
9696
*-------------------------------------------------------------------------
9797
*/
@@ -196,6 +196,7 @@ struct Tuplesortstate
196196
boolrandomAccess;/* did caller request random access? */
197197
boolbounded;/* did caller specify a maximum number of
198198
* tuples to return? */
199+
boolboundUsed;/* true if we made use of a bounded heap */
199200
intbound;/* if bounded, the maximum number of tuples */
200201
longavailMem;/* remaining memory available, in bytes */
201202
longallowedMem;/* total memory allowed, in bytes */
@@ -505,6 +506,8 @@ tuplesort_begin_common(int workMem, bool randomAccess)
505506

506507
state->status=TSS_INITIAL;
507508
state->randomAccess=randomAccess;
509+
state->bounded= false;
510+
state->boundUsed= false;
508511
state->allowedMem=workMem*1024L;
509512
state->availMem=state->allowedMem;
510513
state->sortcontext=sortcontext;
@@ -2113,6 +2116,64 @@ tuplesort_restorepos(Tuplesortstate *state)
21132116
MemoryContextSwitchTo(oldcontext);
21142117
}
21152118

2119+
/*
2120+
* tuplesort_explain - produce a line of information for EXPLAIN ANALYZE
2121+
*
2122+
* This can be called after tuplesort_performsort() finishes to obtain
2123+
* printable summary information about how the sort was performed.
2124+
*
2125+
* The result is a palloc'd string.
2126+
*/
2127+
char*
2128+
tuplesort_explain(Tuplesortstate*state)
2129+
{
2130+
char*result= (char*)palloc(100);
2131+
longspaceUsed;
2132+
2133+
/*
2134+
* Note: it might seem we should print both memory and disk usage for a
2135+
* disk-based sort. However, the current code doesn't track memory space
2136+
* accurately once we have begun to return tuples to the caller (since
2137+
* we don't account for pfree's the caller is expected to do), so we
2138+
* cannot rely on availMem in a disk sort. This does not seem worth the
2139+
* overhead to fix. Is it worth creating an API for the memory context
2140+
* code to tell us how much is actually used in sortcontext?
2141+
*/
2142+
if (state->tapeset)
2143+
spaceUsed=LogicalTapeSetBlocks(state->tapeset)* (BLCKSZ /1024);
2144+
else
2145+
spaceUsed= (state->allowedMem-state->availMem+1023) /1024;
2146+
2147+
switch (state->status)
2148+
{
2149+
caseTSS_SORTEDINMEM:
2150+
if (state->boundUsed)
2151+
snprintf(result,100,
2152+
"Sort Method: top-N heapsort Memory: %ldkB",
2153+
spaceUsed);
2154+
else
2155+
snprintf(result,100,
2156+
"Sort Method: quicksort Memory: %ldkB",
2157+
spaceUsed);
2158+
break;
2159+
caseTSS_SORTEDONTAPE:
2160+
snprintf(result,100,
2161+
"Sort Method: external sort Disk: %ldkB",
2162+
spaceUsed);
2163+
break;
2164+
caseTSS_FINALMERGE:
2165+
snprintf(result,100,
2166+
"Sort Method: external merge Disk: %ldkB",
2167+
spaceUsed);
2168+
break;
2169+
default:
2170+
snprintf(result,100,"sort still in progress");
2171+
break;
2172+
}
2173+
2174+
returnresult;
2175+
}
2176+
21162177

21172178
/*
21182179
* Heap manipulation routines, per Knuth's Algorithm 5.2.3H.
@@ -2216,6 +2277,7 @@ sort_bounded_heap(Tuplesortstate *state)
22162277
REVERSEDIRECTION(state);
22172278

22182279
state->status=TSS_SORTEDINMEM;
2280+
state->boundUsed= true;
22192281
}
22202282

22212283
/*

‎src/include/utils/tuplesort.h

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -13,7 +13,7 @@
1313
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
1414
* Portions Copyright (c) 1994, Regents of the University of California
1515
*
16-
* $PostgreSQL: pgsql/src/include/utils/tuplesort.h,v 1.26 2007/05/0401:13:45 tgl Exp $
16+
* $PostgreSQL: pgsql/src/include/utils/tuplesort.h,v 1.27 2007/05/0421:29:53 tgl Exp $
1717
*
1818
*-------------------------------------------------------------------------
1919
*/
@@ -74,6 +74,8 @@ extern bool tuplesort_getdatum(Tuplesortstate *state, bool forward,
7474

7575
externvoidtuplesort_end(Tuplesortstate*state);
7676

77+
externchar*tuplesort_explain(Tuplesortstate*state);
78+
7779
externinttuplesort_merge_order(longallowedMem);
7880

7981
/*

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