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Commit 24d8595

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jeff-davisjeff-davis
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Introduce LogicalTapeSetExtend().
Increases the number of tapes in a logical tape set. This will be important for disk-based hash aggregation, because the maximum number of tapes is not known ahead of time. While discussing this change, it was observed to regress the performance of Sort for at least one test case. The performance regression was because some versions of GCC switch to an inlined version of memcpy() in LogicalTapeWrite() after this change. No performance regression for clang was observed. Because the regression is due to an arbitrary decision by the compiler, I decided it shouldn't hold up this change. If it needs to be fixed, we can find a workaround. Author: Adam Lee, Jeff Davis Discussion: https://postgr.es/m/e54bfec11c59689890f277722aaaabd05f78e22c.camel%40j-davis.com
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‎src/backend/utils/sort/logtape.c‎

Copy file name to clipboardExpand all lines: src/backend/utils/sort/logtape.c
+46-27Lines changed: 46 additions & 27 deletions
Original file line numberDiff line numberDiff line change
@@ -191,8 +191,8 @@ struct LogicalTapeSet
191191
Size freeBlocksLen; /* current allocated length of freeBlocks[] */
192192

193193
/* The array of logical tapes. */
194-
int nTapes; /* # of logical tapes in set */
195-
LogicalTape tapes[FLEXIBLE_ARRAY_MEMBER]; /* has nTapes nentries */
194+
int nTapes; /* # of logical tapes in set */
195+
LogicalTape *tapes; /* has nTapes nentries */
196196
};
197197

198198
static void ltsWriteBlock(LogicalTapeSet *lts, long blocknum, void *buffer);
@@ -201,6 +201,7 @@ static long ltsGetFreeBlock(LogicalTapeSet *lts);
201201
static void ltsReleaseBlock(LogicalTapeSet *lts, long blocknum);
202202
static void ltsConcatWorkerTapes(LogicalTapeSet *lts, TapeShare *shared,
203203
SharedFileSet *fileset);
204+
static void ltsInitTape(LogicalTape *lt);
204205
static void ltsInitReadBuffer(LogicalTapeSet *lts, LogicalTape *lt);
205206

206207

@@ -536,6 +537,27 @@ ltsConcatWorkerTapes(LogicalTapeSet *lts, TapeShare *shared,
536537
lts->nHoleBlocks = lts->nBlocksAllocated - nphysicalblocks;
537538
}
538539

540+
/*
541+
* Initialize per-tape struct. Note we allocate the I/O buffer lazily.
542+
*/
543+
static void
544+
ltsInitTape(LogicalTape *lt)
545+
{
546+
lt->writing = true;
547+
lt->frozen = false;
548+
lt->dirty = false;
549+
lt->firstBlockNumber = -1L;
550+
lt->curBlockNumber = -1L;
551+
lt->nextBlockNumber = -1L;
552+
lt->offsetBlockNumber = 0L;
553+
lt->buffer = NULL;
554+
lt->buffer_size = 0;
555+
/* palloc() larger than MaxAllocSize would fail */
556+
lt->max_size = MaxAllocSize;
557+
lt->pos = 0;
558+
lt->nbytes = 0;
559+
}
560+
539561
/*
540562
* Lazily allocate and initialize the read buffer. This avoids waste when many
541563
* tapes are open at once, but not all are active between rewinding and
@@ -579,15 +601,13 @@ LogicalTapeSetCreate(int ntapes, TapeShare *shared, SharedFileSet *fileset,
579601
int worker)
580602
{
581603
LogicalTapeSet *lts;
582-
LogicalTape *lt;
583604
int i;
584605

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/*
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* Create top-level struct including per-tape LogicalTape structs.
587608
*/
588609
Assert(ntapes > 0);
589-
lts = (LogicalTapeSet *) palloc(offsetof(LogicalTapeSet, tapes) +
590-
ntapes * sizeof(LogicalTape));
610+
lts = (LogicalTapeSet *) palloc(sizeof(LogicalTapeSet));
591611
lts->nBlocksAllocated = 0L;
592612
lts->nBlocksWritten = 0L;
593613
lts->nHoleBlocks = 0L;
@@ -596,30 +616,10 @@ LogicalTapeSetCreate(int ntapes, TapeShare *shared, SharedFileSet *fileset,
596616
lts->freeBlocks = (long *) palloc(lts->freeBlocksLen * sizeof(long));
597617
lts->nFreeBlocks = 0;
598618
lts->nTapes = ntapes;
619+
lts->tapes = (LogicalTape *) palloc(ntapes * sizeof(LogicalTape));
599620

600-
/*
601-
* Initialize per-tape structs. Note we allocate the I/O buffer and the
602-
* first block for a tape only when it is first actually written to. This
603-
* avoids wasting memory space when tuplesort.c overestimates the number
604-
* of tapes needed.
605-
*/
606621
for (i = 0; i < ntapes; i++)
607-
{
608-
lt = &lts->tapes[i];
609-
lt->writing = true;
610-
lt->frozen = false;
611-
lt->dirty = false;
612-
lt->firstBlockNumber = -1L;
613-
lt->curBlockNumber = -1L;
614-
lt->nextBlockNumber = -1L;
615-
lt->offsetBlockNumber = 0L;
616-
lt->buffer = NULL;
617-
lt->buffer_size = 0;
618-
/* palloc() larger than MaxAllocSize would fail */
619-
lt->max_size = MaxAllocSize;
620-
lt->pos = 0;
621-
lt->nbytes = 0;
622-
}
622+
ltsInitTape(&lts->tapes[i]);
623623

624624
/*
625625
* Create temp BufFile storage as required.
@@ -1004,6 +1004,25 @@ LogicalTapeFreeze(LogicalTapeSet *lts, int tapenum, TapeShare *share)
10041004
}
10051005
}
10061006

1007+
/*
1008+
* Add additional tapes to this tape set. Not intended to be used when any
1009+
* tapes are frozen.
1010+
*/
1011+
void
1012+
LogicalTapeSetExtend(LogicalTapeSet *lts, int nAdditional)
1013+
{
1014+
int i;
1015+
int nTapesOrig = lts->nTapes;
1016+
1017+
lts->nTapes += nAdditional;
1018+
1019+
lts->tapes = (LogicalTape *) repalloc(
1020+
lts->tapes, lts->nTapes * sizeof(LogicalTape));
1021+
1022+
for (i = nTapesOrig; i < lts->nTapes; i++)
1023+
ltsInitTape(&lts->tapes[i]);
1024+
}
1025+
10071026
/*
10081027
* Backspace the tape a given number of bytes. (We also support a more
10091028
* general seek interface, see below.)
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‎src/include/utils/logtape.h‎

Copy file name to clipboardExpand all lines: src/include/utils/logtape.h
+1Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -67,6 +67,7 @@ extern void LogicalTapeRewindForRead(LogicalTapeSet *lts, int tapenum,
6767
extern void LogicalTapeRewindForWrite(LogicalTapeSet *lts, int tapenum);
6868
extern void LogicalTapeFreeze(LogicalTapeSet *lts, int tapenum,
6969
TapeShare *share);
70+
extern void LogicalTapeSetExtend(LogicalTapeSet *lts, int nAdditional);
7071
extern size_t LogicalTapeBackspace(LogicalTapeSet *lts, int tapenum,
7172
size_t size);
7273
extern void LogicalTapeSeek(LogicalTapeSet *lts, int tapenum,

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