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Commit93106d7

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logtape.c: do not preallocate for tapes when sorting
The preallocation logic is only useful for HashAgg, so disable it whensorting.Also, adjust an out-of-date comment.Reviewed-by: Peter GeogheganDiscussion:https://postgr.es/m/CAH2-Wzn_o7tE2+hRVvwSFghRb75AJ5g-nqGzDUqLYMexjOAe=g@mail.gmail.comBackpatch-through: 13
1 parentaeb7811 commit93106d7

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4 files changed

+32
-18
lines changed

4 files changed

+32
-18
lines changed

‎src/backend/executor/nodeAgg.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2882,7 +2882,7 @@ hashagg_tapeinfo_init(AggState *aggstate)
28822882
HashTapeInfo*tapeinfo=palloc(sizeof(HashTapeInfo));
28832883
intinit_tapes=16;/* expanded dynamically */
28842884

2885-
tapeinfo->tapeset=LogicalTapeSetCreate(init_tapes,NULL,NULL,-1);
2885+
tapeinfo->tapeset=LogicalTapeSetCreate(init_tapes,true,NULL,NULL,-1);
28862886
tapeinfo->ntapes=init_tapes;
28872887
tapeinfo->nfreetapes=init_tapes;
28882888
tapeinfo->freetapes_alloc=init_tapes;

‎src/backend/utils/sort/logtape.c

Lines changed: 25 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -210,6 +210,7 @@ struct LogicalTapeSet
210210
long*freeBlocks;/* resizable array holding minheap */
211211
longnFreeBlocks;/* # of currently free blocks */
212212
SizefreeBlocksLen;/* current allocated length of freeBlocks[] */
213+
boolenable_prealloc;/* preallocate write blocks? */
213214

214215
/* The array of logical tapes. */
215216
intnTapes;/* # of logical tapes in set */
@@ -218,6 +219,7 @@ struct LogicalTapeSet
218219

219220
staticvoidltsWriteBlock(LogicalTapeSet*lts,longblocknum,void*buffer);
220221
staticvoidltsReadBlock(LogicalTapeSet*lts,longblocknum,void*buffer);
222+
staticlongltsGetBlock(LogicalTapeSet*lts,LogicalTape*lt);
221223
staticlongltsGetFreeBlock(LogicalTapeSet*lts);
222224
staticlongltsGetPreallocBlock(LogicalTapeSet*lts,LogicalTape*lt);
223225
staticvoidltsReleaseBlock(LogicalTapeSet*lts,longblocknum);
@@ -240,12 +242,8 @@ ltsWriteBlock(LogicalTapeSet *lts, long blocknum, void *buffer)
240242
* that's past the current end of file, fill the space between the current
241243
* end of file and the target block with zeros.
242244
*
243-
* This should happen rarely, otherwise you are not writing very
244-
* sequentially. In current use, this only happens when the sort ends
245-
* writing a run, and switches to another tape. The last block of the
246-
* previous tape isn't flushed to disk until the end of the sort, so you
247-
* get one-block hole, where the last block of the previous tape will
248-
* later go.
245+
* This can happen either when tapes preallocate blocks; or for the last
246+
* block of a tape which might not have been flushed.
249247
*
250248
* Note that BufFile concatenation can leave "holes" in BufFile between
251249
* worker-owned block ranges. These are tracked for reporting purposes
@@ -371,8 +369,20 @@ parent_offset(unsigned long i)
371369
}
372370

373371
/*
374-
* Select the lowest currently unused block by taking the first element from
375-
* the freelist min heap.
372+
* Get the next block for writing.
373+
*/
374+
staticlong
375+
ltsGetBlock(LogicalTapeSet*lts,LogicalTape*lt)
376+
{
377+
if (lts->enable_prealloc)
378+
returnltsGetPreallocBlock(lts,lt);
379+
else
380+
returnltsGetFreeBlock(lts);
381+
}
382+
383+
/*
384+
* Select the lowest currently unused block from the tape set's global free
385+
* list min heap.
376386
*/
377387
staticlong
378388
ltsGetFreeBlock(LogicalTapeSet*lts)
@@ -428,7 +438,8 @@ ltsGetFreeBlock(LogicalTapeSet *lts)
428438

429439
/*
430440
* Return the lowest free block number from the tape's preallocation list.
431-
* Refill the preallocation list if necessary.
441+
* Refill the preallocation list with blocks from the tape set's free list if
442+
* necessary.
432443
*/
433444
staticlong
434445
ltsGetPreallocBlock(LogicalTapeSet*lts,LogicalTape*lt)
@@ -669,8 +680,8 @@ ltsInitReadBuffer(LogicalTapeSet *lts, LogicalTape *lt)
669680
* infrastructure that may be lifted in the future.
670681
*/
671682
LogicalTapeSet*
672-
LogicalTapeSetCreate(intntapes,TapeShare*shared,SharedFileSet*fileset,
673-
intworker)
683+
LogicalTapeSetCreate(intntapes,boolpreallocate,TapeShare*shared,
684+
SharedFileSet*fileset,intworker)
674685
{
675686
LogicalTapeSet*lts;
676687
inti;
@@ -687,6 +698,7 @@ LogicalTapeSetCreate(int ntapes, TapeShare *shared, SharedFileSet *fileset,
687698
lts->freeBlocksLen=32;/* reasonable initial guess */
688699
lts->freeBlocks= (long*)palloc(lts->freeBlocksLen*sizeof(long));
689700
lts->nFreeBlocks=0;
701+
lts->enable_prealloc=preallocate;
690702
lts->nTapes=ntapes;
691703
lts->tapes= (LogicalTape*)palloc(ntapes*sizeof(LogicalTape));
692704

@@ -780,7 +792,7 @@ LogicalTapeWrite(LogicalTapeSet *lts, int tapenum,
780792
Assert(lt->firstBlockNumber==-1);
781793
Assert(lt->pos==0);
782794

783-
lt->curBlockNumber=ltsGetPreallocBlock(lts,lt);
795+
lt->curBlockNumber=ltsGetBlock(lts,lt);
784796
lt->firstBlockNumber=lt->curBlockNumber;
785797

786798
TapeBlockGetTrailer(lt->buffer)->prev=-1L;
@@ -804,7 +816,7 @@ LogicalTapeWrite(LogicalTapeSet *lts, int tapenum,
804816
* First allocate the next block, so that we can store it in the
805817
* 'next' pointer of this block.
806818
*/
807-
nextBlockNumber=ltsGetPreallocBlock(lts,lt);
819+
nextBlockNumber=ltsGetBlock(lts,lt);
808820

809821
/* set the next-pointer and dump the current block. */
810822
TapeBlockGetTrailer(lt->buffer)->next=nextBlockNumber;

‎src/backend/utils/sort/tuplesort.c

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -2591,7 +2591,7 @@ inittapes(Tuplesortstate *state, bool mergeruns)
25912591
/* Create the tape set and allocate the per-tape data arrays */
25922592
inittapestate(state,maxTapes);
25932593
state->tapeset=
2594-
LogicalTapeSetCreate(maxTapes,NULL,
2594+
LogicalTapeSetCreate(maxTapes,false,NULL,
25952595
state->shared ?&state->shared->fileset :NULL,
25962596
state->worker);
25972597

@@ -4657,8 +4657,9 @@ leader_takeover_tapes(Tuplesortstate *state)
46574657
* randomAccess is disallowed for parallel sorts.
46584658
*/
46594659
inittapestate(state,nParticipants+1);
4660-
state->tapeset=LogicalTapeSetCreate(nParticipants+1,shared->tapes,
4661-
&shared->fileset,state->worker);
4660+
state->tapeset=LogicalTapeSetCreate(nParticipants+1, false,
4661+
shared->tapes,&shared->fileset,
4662+
state->worker);
46624663

46634664
/* mergeruns() relies on currentRun for # of runs (in one-pass cases) */
46644665
state->currentRun=nParticipants;

‎src/include/utils/logtape.h

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -54,7 +54,8 @@ typedef struct TapeShare
5454
* prototypes for functions in logtape.c
5555
*/
5656

57-
externLogicalTapeSet*LogicalTapeSetCreate(intntapes,TapeShare*shared,
57+
externLogicalTapeSet*LogicalTapeSetCreate(intntapes,boolpreallocate,
58+
TapeShare*shared,
5859
SharedFileSet*fileset,intworker);
5960
externvoidLogicalTapeSetClose(LogicalTapeSet*lts);
6061
externvoidLogicalTapeSetForgetFreeSpace(LogicalTapeSet*lts);

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