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Commite9fd041

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Move heap-specific detoasting logic into a separate function.
The new function, heap_fetch_toast_slice, is shared betweentoast_fetch_datum_slice and toast_fetch_datum, and does all thework of scanning the TOAST table, fetching chunks, and storingthem into the space allocated for the result varlena.As an incidental side effect, this allows toast_fetch_datum_sliceto perform the scan with only a single scankey if all chunks arebeing fetched, which might have some tiny performance benefit.Discussion:http://postgr.es/m/CA+TgmobBzxwFojJ0zV0Own3dr09y43hp+OzU2VW+nos4PMXWEg@mail.gmail.com
1 parentbf7427b commite9fd041

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1 file changed

+71
-173
lines changed

1 file changed

+71
-173
lines changed

‎src/backend/access/common/detoast.c

Lines changed: 71 additions & 173 deletions
Original file line numberDiff line numberDiff line change
@@ -27,6 +27,9 @@ static struct varlena *toast_fetch_datum(struct varlena *attr);
2727
staticstructvarlena*toast_fetch_datum_slice(structvarlena*attr,
2828
int32sliceoffset,
2929
int32slicelength);
30+
staticvoidheap_fetch_toast_slice(Relationtoastrel,Oidvalueid,
31+
int32attrsize,int32sliceoffset,
32+
int32slicelength,structvarlena*result);
3033
staticstructvarlena*toast_decompress_datum(structvarlena*attr);
3134
staticstructvarlena*toast_decompress_datum_slice(structvarlena*attr,int32slicelength);
3235

@@ -325,19 +328,9 @@ static struct varlena *
325328
toast_fetch_datum(structvarlena*attr)
326329
{
327330
Relationtoastrel;
328-
Relation*toastidxs;
329-
ScanKeyDatatoastkey;
330-
SysScanDesctoastscan;
331-
HeapTuplettup;
332-
TupleDesctoasttupDesc;
333331
structvarlena*result;
334332
structvaratt_externaltoast_pointer;
335333
int32attrsize;
336-
int32expectedchunk;
337-
int32totalchunks;
338-
intnum_indexes;
339-
intvalidIndex;
340-
SnapshotDataSnapshotToast;
341334

342335
if (!VARATT_IS_EXTERNAL_ONDISK(attr))
343336
elog(ERROR,"toast_fetch_datum shouldn't be called for non-ondisk datums");
@@ -346,7 +339,6 @@ toast_fetch_datum(struct varlena *attr)
346339
VARATT_EXTERNAL_GET_POINTER(toast_pointer,attr);
347340

348341
attrsize=toast_pointer.va_extsize;
349-
totalchunks= ((attrsize-1) /TOAST_MAX_CHUNK_SIZE)+1;
350342

351343
result= (structvarlena*)palloc(attrsize+VARHDRSZ);
352344

@@ -355,130 +347,19 @@ toast_fetch_datum(struct varlena *attr)
355347
else
356348
SET_VARSIZE(result,attrsize+VARHDRSZ);
357349

350+
if (attrsize==0)
351+
returnresult;/* Probably shouldn't happen, but just in case. */
352+
358353
/*
359354
* Open the toast relation and its indexes
360355
*/
361356
toastrel=table_open(toast_pointer.va_toastrelid,AccessShareLock);
362-
toasttupDesc=toastrel->rd_att;
363-
364-
/* Look for the valid index of the toast relation */
365-
validIndex=toast_open_indexes(toastrel,
366-
AccessShareLock,
367-
&toastidxs,
368-
&num_indexes);
369357

370-
/*
371-
* Setup a scan key to fetch from the index by va_valueid
372-
*/
373-
ScanKeyInit(&toastkey,
374-
(AttrNumber)1,
375-
BTEqualStrategyNumber,F_OIDEQ,
376-
ObjectIdGetDatum(toast_pointer.va_valueid));
358+
/* Fetch all chunks */
359+
heap_fetch_toast_slice(toastrel,toast_pointer.va_valueid,attrsize,0,
360+
attrsize,result);
377361

378-
/*
379-
* Read the chunks by index
380-
*
381-
* Note that because the index is actually on (valueid, chunkidx) we will
382-
* see the chunks in chunkidx order, even though we didn't explicitly ask
383-
* for it.
384-
*/
385-
expectedchunk=0;
386-
387-
init_toast_snapshot(&SnapshotToast);
388-
toastscan=systable_beginscan_ordered(toastrel,toastidxs[validIndex],
389-
&SnapshotToast,1,&toastkey);
390-
while ((ttup=systable_getnext_ordered(toastscan,ForwardScanDirection))!=NULL)
391-
{
392-
int32curchunk;
393-
Pointerchunk;
394-
boolisnull;
395-
char*chunkdata;
396-
int32chunksize;
397-
int32expected_size;
398-
399-
/*
400-
* Have a chunk, extract the sequence number and the data
401-
*/
402-
curchunk=DatumGetInt32(fastgetattr(ttup,2,toasttupDesc,&isnull));
403-
Assert(!isnull);
404-
chunk=DatumGetPointer(fastgetattr(ttup,3,toasttupDesc,&isnull));
405-
Assert(!isnull);
406-
if (!VARATT_IS_EXTENDED(chunk))
407-
{
408-
chunksize=VARSIZE(chunk)-VARHDRSZ;
409-
chunkdata=VARDATA(chunk);
410-
}
411-
elseif (VARATT_IS_SHORT(chunk))
412-
{
413-
/* could happen due to heap_form_tuple doing its thing */
414-
chunksize=VARSIZE_SHORT(chunk)-VARHDRSZ_SHORT;
415-
chunkdata=VARDATA_SHORT(chunk);
416-
}
417-
else
418-
{
419-
/* should never happen */
420-
elog(ERROR,"found toasted toast chunk for toast value %u in %s",
421-
toast_pointer.va_valueid,
422-
RelationGetRelationName(toastrel));
423-
chunksize=0;/* keep compiler quiet */
424-
chunkdata=NULL;
425-
}
426-
427-
/*
428-
* Some checks on the data we've found
429-
*/
430-
if (curchunk!=expectedchunk)
431-
ereport(ERROR,
432-
(errcode(ERRCODE_DATA_CORRUPTED),
433-
errmsg_internal("unexpected chunk number %d (expected %d) for toast value %u in %s",
434-
curchunk,expectedchunk,
435-
toast_pointer.va_valueid,
436-
RelationGetRelationName(toastrel))));
437-
if (curchunk>totalchunks-1)
438-
ereport(ERROR,
439-
(errcode(ERRCODE_DATA_CORRUPTED),
440-
errmsg_internal("unexpected chunk number %d (out of range %d..%d) for toast value %u in %s",
441-
curchunk,
442-
0,totalchunks-1,
443-
toast_pointer.va_valueid,
444-
RelationGetRelationName(toastrel))));
445-
expected_size=curchunk<totalchunks-1 ?TOAST_MAX_CHUNK_SIZE
446-
:attrsize- ((totalchunks-1)*TOAST_MAX_CHUNK_SIZE);
447-
if (chunksize!=expected_size)
448-
ereport(ERROR,
449-
(errcode(ERRCODE_DATA_CORRUPTED),
450-
errmsg_internal("unexpected chunk size %d (expected %d) in chunk %d of %d for toast value %u in %s",
451-
chunksize,expected_size,
452-
curchunk,totalchunks,
453-
toast_pointer.va_valueid,
454-
RelationGetRelationName(toastrel))));
455-
456-
/*
457-
* Copy the data into proper place in our result
458-
*/
459-
memcpy(VARDATA(result)+curchunk*TOAST_MAX_CHUNK_SIZE,
460-
chunkdata,
461-
chunksize);
462-
463-
expectedchunk++;
464-
}
465-
466-
/*
467-
* Final checks that we successfully fetched the datum
468-
*/
469-
if (expectedchunk!=totalchunks)
470-
ereport(ERROR,
471-
(errcode(ERRCODE_DATA_CORRUPTED),
472-
errmsg_internal("missing chunk number %d for toast value %u in %s",
473-
expectedchunk,
474-
toast_pointer.va_valueid,
475-
RelationGetRelationName(toastrel))));
476-
477-
/*
478-
* End scan and close relations
479-
*/
480-
systable_endscan_ordered(toastscan);
481-
toast_close_indexes(toastidxs,num_indexes,AccessShareLock);
362+
/* Close toast table */
482363
table_close(toastrel,AccessShareLock);
483364

484365
returnresult;
@@ -500,22 +381,9 @@ toast_fetch_datum_slice(struct varlena *attr, int32 sliceoffset,
500381
int32slicelength)
501382
{
502383
Relationtoastrel;
503-
Relation*toastidxs;
504-
ScanKeyDatatoastkey[3];
505-
intnscankeys;
506-
SysScanDesctoastscan;
507-
HeapTuplettup;
508-
TupleDesctoasttupDesc;
509384
structvarlena*result;
510385
structvaratt_externaltoast_pointer;
511386
int32attrsize;
512-
int32expectedchunk;
513-
intstartchunk;
514-
intendchunk;
515-
inttotalchunks;
516-
intnum_indexes;
517-
intvalidIndex;
518-
SnapshotDataSnapshotToast;
519387

520388
if (!VARATT_IS_EXTERNAL_ONDISK(attr))
521389
elog(ERROR,"toast_fetch_datum_slice shouldn't be called for non-ondisk datums");
@@ -531,7 +399,6 @@ toast_fetch_datum_slice(struct varlena *attr, int32 sliceoffset,
531399
Assert(!VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer)||0==sliceoffset);
532400

533401
attrsize=toast_pointer.va_extsize;
534-
totalchunks= ((attrsize-1) /TOAST_MAX_CHUNK_SIZE)+1;
535402

536403
if (sliceoffset >=attrsize)
537404
{
@@ -560,35 +427,74 @@ toast_fetch_datum_slice(struct varlena *attr, int32 sliceoffset,
560427
if (slicelength==0)
561428
returnresult;/* Can save a lot of work at this point! */
562429

563-
startchunk=sliceoffset /TOAST_MAX_CHUNK_SIZE;
564-
endchunk= (sliceoffset+slicelength-1) /TOAST_MAX_CHUNK_SIZE;
565-
Assert(endchunk<totalchunks);
566-
567-
/*
568-
* Open the toast relation and its indexes
569-
*/
430+
/* Open the toast relation */
570431
toastrel=table_open(toast_pointer.va_toastrelid,AccessShareLock);
571-
toasttupDesc=toastrel->rd_att;
432+
433+
/* Fetch all chunks */
434+
heap_fetch_toast_slice(toastrel,toast_pointer.va_valueid,attrsize,
435+
sliceoffset,slicelength,result);
436+
437+
/* Close toast table */
438+
table_close(toastrel,AccessShareLock);
439+
440+
returnresult;
441+
}
442+
443+
/*
444+
* Fetch a TOAST slice from a heap table.
445+
*
446+
* toastrel is the relation from which chunks are to be fetched.
447+
* valueid identifies the TOAST value from which chunks are being fetched.
448+
* attrsize is the total size of the TOAST value.
449+
* sliceoffset is the byte offset within the TOAST value from which to fetch.
450+
* slicelength is the number of bytes to be fetched from the TOAST value.
451+
* result is the varlena into which the results should be written.
452+
*/
453+
staticvoid
454+
heap_fetch_toast_slice(Relationtoastrel,Oidvalueid,int32attrsize,
455+
int32sliceoffset,int32slicelength,
456+
structvarlena*result)
457+
{
458+
Relation*toastidxs;
459+
ScanKeyDatatoastkey[3];
460+
TupleDesctoasttupDesc=toastrel->rd_att;
461+
intnscankeys;
462+
SysScanDesctoastscan;
463+
HeapTuplettup;
464+
int32expectedchunk;
465+
int32totalchunks= ((attrsize-1) /TOAST_MAX_CHUNK_SIZE)+1;
466+
intstartchunk;
467+
intendchunk;
468+
intnum_indexes;
469+
intvalidIndex;
470+
SnapshotDataSnapshotToast;
572471

573472
/* Look for the valid index of toast relation */
574473
validIndex=toast_open_indexes(toastrel,
575474
AccessShareLock,
576475
&toastidxs,
577476
&num_indexes);
578477

478+
startchunk=sliceoffset /TOAST_MAX_CHUNK_SIZE;
479+
endchunk= (sliceoffset+slicelength-1) /TOAST_MAX_CHUNK_SIZE;
480+
Assert(endchunk <=totalchunks);
481+
579482
/*
580483
* Setup a scan key to fetch from the index. This is either two keys or
581484
* three depending on the number of chunks.
582485
*/
583486
ScanKeyInit(&toastkey[0],
584487
(AttrNumber)1,
585488
BTEqualStrategyNumber,F_OIDEQ,
586-
ObjectIdGetDatum(toast_pointer.va_valueid));
489+
ObjectIdGetDatum(valueid));
587490

588491
/*
589-
* Use equality condition for one chunk, a range condition otherwise:
492+
* No additional condition if fetching all chunks. Otherwise, use an
493+
* equality condition for one chunk, and a range condition otherwise.
590494
*/
591-
if (startchunk==endchunk)
495+
if (startchunk==0&&endchunk==totalchunks-1)
496+
nscankeys=1;
497+
elseif (startchunk==endchunk)
592498
{
593499
ScanKeyInit(&toastkey[1],
594500
(AttrNumber)2,
@@ -609,15 +515,17 @@ toast_fetch_datum_slice(struct varlena *attr, int32 sliceoffset,
609515
nscankeys=3;
610516
}
611517

518+
/* Prepare for scan */
519+
init_toast_snapshot(&SnapshotToast);
520+
toastscan=systable_beginscan_ordered(toastrel,toastidxs[validIndex],
521+
&SnapshotToast,nscankeys,toastkey);
522+
612523
/*
613524
* Read the chunks by index
614525
*
615526
* The index is on (valueid, chunkidx) so they will come in order
616527
*/
617-
init_toast_snapshot(&SnapshotToast);
618528
expectedchunk=startchunk;
619-
toastscan=systable_beginscan_ordered(toastrel,toastidxs[validIndex],
620-
&SnapshotToast,nscankeys,toastkey);
621529
while ((ttup=systable_getnext_ordered(toastscan,ForwardScanDirection))!=NULL)
622530
{
623531
int32curchunk;
@@ -651,8 +559,7 @@ toast_fetch_datum_slice(struct varlena *attr, int32 sliceoffset,
651559
{
652560
/* should never happen */
653561
elog(ERROR,"found toasted toast chunk for toast value %u in %s",
654-
toast_pointer.va_valueid,
655-
RelationGetRelationName(toastrel));
562+
valueid,RelationGetRelationName(toastrel));
656563
chunksize=0;/* keep compiler quiet */
657564
chunkdata=NULL;
658565
}
@@ -664,16 +571,14 @@ toast_fetch_datum_slice(struct varlena *attr, int32 sliceoffset,
664571
ereport(ERROR,
665572
(errcode(ERRCODE_DATA_CORRUPTED),
666573
errmsg_internal("unexpected chunk number %d (expected %d) for toast value %u in %s",
667-
curchunk,expectedchunk,
668-
toast_pointer.va_valueid,
574+
curchunk,expectedchunk,valueid,
669575
RelationGetRelationName(toastrel))));
670576
if (curchunk>endchunk)
671577
ereport(ERROR,
672578
(errcode(ERRCODE_DATA_CORRUPTED),
673579
errmsg_internal("unexpected chunk number %d (out of range %d..%d) for toast value %u in %s",
674580
curchunk,
675-
startchunk,endchunk,
676-
toast_pointer.va_valueid,
581+
startchunk,endchunk,valueid,
677582
RelationGetRelationName(toastrel))));
678583
expected_size=curchunk<totalchunks-1 ?TOAST_MAX_CHUNK_SIZE
679584
:attrsize- ((totalchunks-1)*TOAST_MAX_CHUNK_SIZE);
@@ -682,8 +587,7 @@ toast_fetch_datum_slice(struct varlena *attr, int32 sliceoffset,
682587
(errcode(ERRCODE_DATA_CORRUPTED),
683588
errmsg_internal("unexpected chunk size %d (expected %d) in chunk %d of %d for toast value %u in %s",
684589
chunksize,expected_size,
685-
curchunk,totalchunks,
686-
toast_pointer.va_valueid,
590+
curchunk,totalchunks,valueid,
687591
RelationGetRelationName(toastrel))));
688592

689593
/*
@@ -711,18 +615,12 @@ toast_fetch_datum_slice(struct varlena *attr, int32 sliceoffset,
711615
ereport(ERROR,
712616
(errcode(ERRCODE_DATA_CORRUPTED),
713617
errmsg_internal("missing chunk number %d for toast value %u in %s",
714-
expectedchunk,
715-
toast_pointer.va_valueid,
618+
expectedchunk,valueid,
716619
RelationGetRelationName(toastrel))));
717620

718-
/*
719-
* End scan and close relations
720-
*/
621+
/* End scan and close indexes. */
721622
systable_endscan_ordered(toastscan);
722623
toast_close_indexes(toastidxs,num_indexes,AccessShareLock);
723-
table_close(toastrel,AccessShareLock);
724-
725-
returnresult;
726624
}
727625

728626
/* ----------

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