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Add a line to the EXPLAIN ANALYZE output for a Sort node, showing the

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actual sort strategy and amount of space used.  By popular demand.
This commit is contained in:
Tom Lane
2007-05-04 21:29:53 +00:00
parent c7464720a3
commit d2a4a4069f
3 changed files with 94 additions and 3 deletions
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64
src/backend/utils/sort/tuplesort.c
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@@ -91,7 +91,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/sort/tuplesort.c,v 1.75 2007/05/04 01:13:44 tgl Exp $
* $PostgreSQL: pgsql/src/backend/utils/sort/tuplesort.c,v 1.76 2007/05/04 21:29:53 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -196,6 +196,7 @@ struct Tuplesortstate
bool randomAccess; /* did caller request random access? */
bool bounded; /* did caller specify a maximum number of
* tuples to return? */
bool boundUsed; /* true if we made use of a bounded heap */
int bound; /* if bounded, the maximum number of tuples */
long availMem; /* remaining memory available, in bytes */
long allowedMem; /* total memory allowed, in bytes */
@@ -505,6 +506,8 @@ tuplesort_begin_common(int workMem, bool randomAccess)
state->status = TSS_INITIAL;
state->randomAccess = randomAccess;
state->bounded = false;
state->boundUsed = false;
state->allowedMem = workMem * 1024L;
state->availMem = state->allowedMem;
state->sortcontext = sortcontext;
@@ -2113,6 +2116,64 @@ tuplesort_restorepos(Tuplesortstate *state)
MemoryContextSwitchTo(oldcontext);
}
/*
* tuplesort_explain - produce a line of information for EXPLAIN ANALYZE
*
* This can be called after tuplesort_performsort() finishes to obtain
* printable summary information about how the sort was performed.
*
* The result is a palloc'd string.
*/
char *
tuplesort_explain(Tuplesortstate *state)
{
char *result = (char *) palloc(100);
long spaceUsed;
/*
* Note: it might seem we should print both memory and disk usage for a
* disk-based sort. However, the current code doesn't track memory space
* accurately once we have begun to return tuples to the caller (since
* we don't account for pfree's the caller is expected to do), so we
* cannot rely on availMem in a disk sort. This does not seem worth the
* overhead to fix. Is it worth creating an API for the memory context
* code to tell us how much is actually used in sortcontext?
*/
if (state->tapeset)
spaceUsed = LogicalTapeSetBlocks(state->tapeset) * (BLCKSZ / 1024);
else
spaceUsed = (state->allowedMem - state->availMem + 1023) / 1024;
switch (state->status)
{
case TSS_SORTEDINMEM:
if (state->boundUsed)
snprintf(result, 100,
"Sort Method: top-N heapsort Memory: %ldkB",
spaceUsed);
else
snprintf(result, 100,
"Sort Method: quicksort Memory: %ldkB",
spaceUsed);
break;
case TSS_SORTEDONTAPE:
snprintf(result, 100,
"Sort Method: external sort Disk: %ldkB",
spaceUsed);
break;
case TSS_FINALMERGE:
snprintf(result, 100,
"Sort Method: external merge Disk: %ldkB",
spaceUsed);
break;
default:
snprintf(result, 100, "sort still in progress");
break;
}
return result;
}
/*
* Heap manipulation routines, per Knuth's Algorithm 5.2.3H.
@@ -2216,6 +2277,7 @@ sort_bounded_heap(Tuplesortstate *state)
REVERSEDIRECTION(state);
state->status = TSS_SORTEDINMEM;
state->boundUsed = true;
}
/*