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Commit0758964

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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The preallocation logic is only useful for HashAgg, so disable it whensorting.Also, adjust an out-of-date comment.Reviewed-by: Peter GeogheganDiscussion:https://postgr.es/m/CAH2-Wzn_o7tE2+hRVvwSFghRb75AJ5g-nqGzDUqLYMexjOAe=g@mail.gmail.comBackpatch-through: 13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 parent7634bd4 commit0758964

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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
@@ -212,6 +212,7 @@ struct LogicalTapeSet
212212
long*freeBlocks;/* resizable array holding minheap */
213213
longnFreeBlocks;/* # of currently free blocks */
214214
SizefreeBlocksLen;/* current allocated length of freeBlocks[] */
215+
boolenable_prealloc;/* preallocate write blocks? */
215216

216217
/* The array of logical tapes. */
217218
intnTapes;/* # of logical tapes in set */
@@ -220,6 +221,7 @@ struct LogicalTapeSet
220221

221222
staticvoidltsWriteBlock(LogicalTapeSet*lts,longblocknum,void*buffer);
222223
staticvoidltsReadBlock(LogicalTapeSet*lts,longblocknum,void*buffer);
224+
staticlongltsGetBlock(LogicalTapeSet*lts,LogicalTape*lt);
223225
staticlongltsGetFreeBlock(LogicalTapeSet*lts);
224226
staticlongltsGetPreallocBlock(LogicalTapeSet*lts,LogicalTape*lt);
225227
staticvoidltsReleaseBlock(LogicalTapeSet*lts,longblocknum);
@@ -242,12 +244,8 @@ ltsWriteBlock(LogicalTapeSet *lts, long blocknum, void *buffer)
242244
* that's past the current end of file, fill the space between the current
243245
* end of file and the target block with zeros.
244246
*
245-
* This should happen rarely, otherwise you are not writing very
246-
* sequentially. In current use, this only happens when the sort ends
247-
* writing a run, and switches to another tape. The last block of the
248-
* previous tape isn't flushed to disk until the end of the sort, so you
249-
* get one-block hole, where the last block of the previous tape will
250-
* later go.
247+
* This can happen either when tapes preallocate blocks; or for the last
248+
* block of a tape which might not have been flushed.
251249
*
252250
* Note that BufFile concatenation can leave "holes" in BufFile between
253251
* worker-owned block ranges. These are tracked for reporting purposes
@@ -373,8 +371,20 @@ parent_offset(unsigned long i)
373371
}
374372

375373
/*
376-
* Select the lowest currently unused block by taking the first element from
377-
* the freelist min heap.
374+
* Get the next block for writing.
375+
*/
376+
staticlong
377+
ltsGetBlock(LogicalTapeSet*lts,LogicalTape*lt)
378+
{
379+
if (lts->enable_prealloc)
380+
returnltsGetPreallocBlock(lts,lt);
381+
else
382+
returnltsGetFreeBlock(lts);
383+
}
384+
385+
/*
386+
* Select the lowest currently unused block from the tape set's global free
387+
* list min heap.
378388
*/
379389
staticlong
380390
ltsGetFreeBlock(LogicalTapeSet*lts)
@@ -430,7 +440,8 @@ ltsGetFreeBlock(LogicalTapeSet *lts)
430440

431441
/*
432442
* Return the lowest free block number from the tape's preallocation list.
433-
* Refill the preallocation list if necessary.
443+
* Refill the preallocation list with blocks from the tape set's free list if
444+
* necessary.
434445
*/
435446
staticlong
436447
ltsGetPreallocBlock(LogicalTapeSet*lts,LogicalTape*lt)
@@ -671,8 +682,8 @@ ltsInitReadBuffer(LogicalTapeSet *lts, LogicalTape *lt)
671682
* infrastructure that may be lifted in the future.
672683
*/
673684
LogicalTapeSet*
674-
LogicalTapeSetCreate(intntapes,TapeShare*shared,SharedFileSet*fileset,
675-
intworker)
685+
LogicalTapeSetCreate(intntapes,boolpreallocate,TapeShare*shared,
686+
SharedFileSet*fileset,intworker)
676687
{
677688
LogicalTapeSet*lts;
678689
inti;
@@ -689,6 +700,7 @@ LogicalTapeSetCreate(int ntapes, TapeShare *shared, SharedFileSet *fileset,
689700
lts->freeBlocksLen=32;/* reasonable initial guess */
690701
lts->freeBlocks= (long*)palloc(lts->freeBlocksLen*sizeof(long));
691702
lts->nFreeBlocks=0;
703+
lts->enable_prealloc=preallocate;
692704
lts->nTapes=ntapes;
693705
lts->tapes= (LogicalTape*)palloc(ntapes*sizeof(LogicalTape));
694706

@@ -782,7 +794,7 @@ LogicalTapeWrite(LogicalTapeSet *lts, int tapenum,
782794
Assert(lt->firstBlockNumber==-1);
783795
Assert(lt->pos==0);
784796

785-
lt->curBlockNumber=ltsGetPreallocBlock(lts,lt);
797+
lt->curBlockNumber=ltsGetBlock(lts,lt);
786798
lt->firstBlockNumber=lt->curBlockNumber;
787799

788800
TapeBlockGetTrailer(lt->buffer)->prev=-1L;
@@ -806,7 +818,7 @@ LogicalTapeWrite(LogicalTapeSet *lts, int tapenum,
806818
* First allocate the next block, so that we can store it in the
807819
* 'next' pointer of this block.
808820
*/
809-
nextBlockNumber=ltsGetPreallocBlock(lts,lt);
821+
nextBlockNumber=ltsGetBlock(lts,lt);
810822

811823
/* set the next-pointer and dump the current block. */
812824
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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