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Commit9b88f27

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Allow index AMs to return either HeapTuple or IndexTuple format during IOS.
Previously, only IndexTuple format was supported for the output data ofan index-only scan. This is fine for btree, which is just returning averbatim index tuple anyway. It's not so fine for SP-GiST, which canreturn reconstructed data that's much larger than a page.To fix, extend the index AM API so that index-only scan data can bereturned in either HeapTuple or IndexTuple format. There's other wayswe could have done it, but this way avoids an API break for index AMsthat aren't concerned with the issue, and it costs little except a couplemore fields in IndexScanDescs.I changed both GiST and SP-GiST to use the HeapTuple method. I'm notvery clear on whether GiST can reconstruct data that's too large for anIndexTuple, but that seems possible, and it's not much of a code change tofix.Per a complaint from Vik Fearing. Reviewed by Jason Li.Discussion:https://postgr.es/m/49527f79-530d-0bfe-3dad-d183596afa92@2ndquadrant.fr
1 parent30df93f commit9b88f27

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11 files changed

+71
-39
lines changed

11 files changed

+71
-39
lines changed

‎doc/src/sgml/indexam.sgml‎

Lines changed: 10 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -551,15 +551,19 @@ amgettuple (IndexScanDesc scan,
551551
<para>
552552
If the index supports <link linkend="indexes-index-only-scans">index-only
553553
scans</link> (i.e., <function>amcanreturn</function> returns TRUE for it),
554-
then on success the AM must also check
555-
<literal>scan-&gt;xs_want_itup</>,and if that is true it must return
556-
the original indexeddatafor the index entry, in the form of an
554+
then on success the AM must also check <literal>scan-&gt;xs_want_itup</>,
555+
and if that is true it must return the originally indexed data for the
556+
index entry. Thedatacan be returned in the form of an
557557
<structname>IndexTuple</> pointer stored at <literal>scan-&gt;xs_itup</>,
558-
with tuple descriptor <literal>scan-&gt;xs_itupdesc</>.
559-
(Management of the data referenced by the pointer is the access method's
558+
with tuple descriptor <literal>scan-&gt;xs_itupdesc</>; or in the form of
559+
a <structname>HeapTuple</> pointer stored at <literal>scan-&gt;xs_hitup</>,
560+
with tuple descriptor <literal>scan-&gt;xs_hitupdesc</>. (The latter
561+
format should be used when reconstructing data that might possibly not fit
562+
into an IndexTuple.) In either case,
563+
management of the data referenced by the pointer is the access method's
560564
responsibility. The data must remain good at least until the next
561565
<function>amgettuple</>, <function>amrescan</>, or <function>amendscan</>
562-
call for the scan.)
566+
call for the scan.
563567
</para>
564568

565569
<para>

‎src/backend/access/gist/gistget.c‎

Lines changed: 9 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -441,12 +441,13 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem, double *myDistances,
441441
so->pageData[so->nPageData].offnum=i;
442442

443443
/*
444-
* In an index-only scan, also fetch the data from the tuple.
444+
* In an index-only scan, also fetch the data from the tuple. The
445+
* reconstructed tuples are stored in pageDataCxt.
445446
*/
446447
if (scan->xs_want_itup)
447448
{
448449
oldcxt=MemoryContextSwitchTo(so->pageDataCxt);
449-
so->pageData[so->nPageData].ftup=
450+
so->pageData[so->nPageData].recontup=
450451
gistFetchTuple(giststate,r,it);
451452
MemoryContextSwitchTo(oldcxt);
452453
}
@@ -478,7 +479,7 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem, double *myDistances,
478479
* In an index-only scan, also fetch the data from the tuple.
479480
*/
480481
if (scan->xs_want_itup)
481-
item->data.heap.ftup=gistFetchTuple(giststate,r,it);
482+
item->data.heap.recontup=gistFetchTuple(giststate,r,it);
482483
}
483484
else
484485
{
@@ -540,11 +541,11 @@ getNextNearest(IndexScanDesc scan)
540541
boolres= false;
541542
inti;
542543

543-
if (scan->xs_itup)
544+
if (scan->xs_hitup)
544545
{
545546
/* free previously returned tuple */
546-
pfree(scan->xs_itup);
547-
scan->xs_itup=NULL;
547+
pfree(scan->xs_hitup);
548+
scan->xs_hitup=NULL;
548549
}
549550

550551
do
@@ -601,7 +602,7 @@ getNextNearest(IndexScanDesc scan)
601602

602603
/* in an index-only scan, also return the reconstructed tuple. */
603604
if (scan->xs_want_itup)
604-
scan->xs_itup=item->data.heap.ftup;
605+
scan->xs_hitup=item->data.heap.recontup;
605606
res= true;
606607
}
607608
else
@@ -685,7 +686,7 @@ gistgettuple(IndexScanDesc scan, ScanDirection dir)
685686

686687
/* in an index-only scan, also return the reconstructed tuple */
687688
if (scan->xs_want_itup)
688-
scan->xs_itup=so->pageData[so->curPageData].ftup;
689+
scan->xs_hitup=so->pageData[so->curPageData].recontup;
689690

690691
so->curPageData++;
691692

‎src/backend/access/gist/gistscan.c‎

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -155,7 +155,7 @@ gistrescan(IndexScanDesc scan, ScanKey key, int nkeys,
155155
* tuple descriptor to represent the returned index tuples and create a
156156
* memory context to hold them during the scan.
157157
*/
158-
if (scan->xs_want_itup&& !scan->xs_itupdesc)
158+
if (scan->xs_want_itup&& !scan->xs_hitupdesc)
159159
{
160160
intnatts;
161161
intattno;
@@ -174,8 +174,9 @@ gistrescan(IndexScanDesc scan, ScanKey key, int nkeys,
174174
scan->indexRelation->rd_opcintype[attno-1],
175175
-1,0);
176176
}
177-
scan->xs_itupdesc=so->giststate->fetchTupdesc;
177+
scan->xs_hitupdesc=so->giststate->fetchTupdesc;
178178

179+
/* Also create a memory context that will hold the returned tuples */
179180
so->pageDataCxt=AllocSetContextCreate(so->giststate->scanCxt,
180181
"GiST page data context",
181182
ALLOCSET_DEFAULT_SIZES);

‎src/backend/access/gist/gistutil.c‎

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -624,9 +624,9 @@ gistFetchAtt(GISTSTATE *giststate, int nkey, Datum k, Relation r)
624624

625625
/*
626626
* Fetch all keys in tuple.
627-
*returnsnewIndexTuple that contains GISTENTRY with fetcheddata
627+
*Returns anewHeapTuple containing the originally-indexeddata.
628628
*/
629-
IndexTuple
629+
HeapTuple
630630
gistFetchTuple(GISTSTATE*giststate,Relationr,IndexTupletuple)
631631
{
632632
MemoryContextoldcxt=MemoryContextSwitchTo(giststate->tempCxt);
@@ -660,7 +660,7 @@ gistFetchTuple(GISTSTATE *giststate, Relation r, IndexTuple tuple)
660660
}
661661
MemoryContextSwitchTo(oldcxt);
662662

663-
returnindex_form_tuple(giststate->fetchTupdesc,fetchatt,isnull);
663+
returnheap_form_tuple(giststate->fetchTupdesc,fetchatt,isnull);
664664
}
665665

666666
float

‎src/backend/access/index/genam.c‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -119,6 +119,8 @@ RelationGetIndexScan(Relation indexRelation, int nkeys, int norderbys)
119119

120120
scan->xs_itup=NULL;
121121
scan->xs_itupdesc=NULL;
122+
scan->xs_hitup=NULL;
123+
scan->xs_hitupdesc=NULL;
122124

123125
ItemPointerSetInvalid(&scan->xs_ctup.t_self);
124126
scan->xs_ctup.t_data=NULL;

‎src/backend/access/index/indexam.c‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -535,8 +535,8 @@ index_getnext_tid(IndexScanDesc scan, ScanDirection direction)
535535
/*
536536
* The AM's amgettuple proc finds the next index entry matching the scan
537537
* keys, and puts the TID into scan->xs_ctup.t_self. It should also set
538-
* scan->xs_recheck and possibly scan->xs_itup, though we pay no attention
539-
* to those fields here.
538+
* scan->xs_recheck and possibly scan->xs_itup/scan->xs_hitup, though we
539+
*pay no attentionto those fields here.
540540
*/
541541
found=scan->indexRelation->rd_amroutine->amgettuple(scan,direction);
542542

‎src/backend/access/spgist/spgscan.c‎

Lines changed: 12 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -92,11 +92,11 @@ resetSpGistScanOpaque(SpGistScanOpaque so)
9292

9393
if (so->want_itup)
9494
{
95-
/* Must pfreeIndexTuples to avoid memory leak */
95+
/* Must pfreereconstructed tuples to avoid memory leak */
9696
inti;
9797

9898
for (i=0;i<so->nPtrs;i++)
99-
pfree(so->indexTups[i]);
99+
pfree(so->reconTups[i]);
100100
}
101101
so->iPtr=so->nPtrs=0;
102102
}
@@ -195,8 +195,8 @@ spgbeginscan(Relation rel, int keysz, int orderbysz)
195195
"SP-GiST search temporary context",
196196
ALLOCSET_DEFAULT_SIZES);
197197

198-
/* Set up indexTupDesc andxs_itupdesc in case it's an index-only scan */
199-
so->indexTupDesc=scan->xs_itupdesc=RelationGetDescr(rel);
198+
/* Set up indexTupDesc andxs_hitupdesc in case it's an index-only scan */
199+
so->indexTupDesc=scan->xs_hitupdesc=RelationGetDescr(rel);
200200

201201
scan->opaque=so;
202202

@@ -591,12 +591,12 @@ storeGettuple(SpGistScanOpaque so, ItemPointer heapPtr,
591591
if (so->want_itup)
592592
{
593593
/*
594-
* Reconstructdesired IndexTuple. We have to copy the datum out of
595-
*the tempcontext anyway, so we may as well create the tuple here.
594+
* Reconstructindex data. We have to copy the datum out of the temp
595+
* context anyway, so we may as well create the tuple here.
596596
*/
597-
so->indexTups[so->nPtrs]=index_form_tuple(so->indexTupDesc,
598-
&leafValue,
599-
&isnull);
597+
so->reconTups[so->nPtrs]=heap_form_tuple(so->indexTupDesc,
598+
&leafValue,
599+
&isnull);
600600
}
601601
so->nPtrs++;
602602
}
@@ -619,18 +619,18 @@ spggettuple(IndexScanDesc scan, ScanDirection dir)
619619
/* continuing to return tuples from a leaf page */
620620
scan->xs_ctup.t_self=so->heapPtrs[so->iPtr];
621621
scan->xs_recheck=so->recheck[so->iPtr];
622-
scan->xs_itup=so->indexTups[so->iPtr];
622+
scan->xs_hitup=so->reconTups[so->iPtr];
623623
so->iPtr++;
624624
return true;
625625
}
626626

627627
if (so->want_itup)
628628
{
629-
/* Must pfreeIndexTuples to avoid memory leak */
629+
/* Must pfreereconstructed tuples to avoid memory leak */
630630
inti;
631631

632632
for (i=0;i<so->nPtrs;i++)
633-
pfree(so->indexTups[i]);
633+
pfree(so->reconTups[i]);
634634
}
635635
so->iPtr=so->nPtrs=0;
636636

‎src/backend/executor/nodeIndexonlyscan.c‎

Lines changed: 19 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -149,9 +149,26 @@ IndexOnlyNext(IndexOnlyScanState *node)
149149
}
150150

151151
/*
152-
* Fill the scan tuple slot with data from the index.
152+
* Fill the scan tuple slot with data from the index. This might be
153+
* provided in either HeapTuple or IndexTuple format. Conceivably an
154+
* index AM might fill both fields, in which case we prefer the heap
155+
* format, since it's probably a bit cheaper to fill a slot from.
153156
*/
154-
StoreIndexTuple(slot,scandesc->xs_itup,scandesc->xs_itupdesc);
157+
if (scandesc->xs_hitup)
158+
{
159+
/*
160+
* We don't take the trouble to verify that the provided tuple has
161+
* exactly the slot's format, but it seems worth doing a quick
162+
* check on the number of fields.
163+
*/
164+
Assert(slot->tts_tupleDescriptor->natts==
165+
scandesc->xs_hitupdesc->natts);
166+
ExecStoreTuple(scandesc->xs_hitup,slot,InvalidBuffer, false);
167+
}
168+
elseif (scandesc->xs_itup)
169+
StoreIndexTuple(slot,scandesc->xs_itup,scandesc->xs_itupdesc);
170+
else
171+
elog(ERROR,"no data returned for index-only scan");
155172

156173
/*
157174
* If the index was lossy, we have to recheck the index quals.

‎src/include/access/gist_private.h‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -119,7 +119,7 @@ typedef struct GISTSearchHeapItem
119119
ItemPointerDataheapPtr;
120120
boolrecheck;/* T if quals must be rechecked */
121121
boolrecheckDistances;/* T if distances must be rechecked */
122-
IndexTupleftup;/* datafetched back from the index, used in
122+
HeapTuplerecontup;/* datareconstructed from the index, used in
123123
* index-only scans */
124124
OffsetNumberoffnum;/* track offset in page to mark tuple as
125125
* LP_DEAD */
@@ -477,7 +477,7 @@ extern void gistMakeUnionItVec(GISTSTATE *giststate, IndexTuple *itvec, int len,
477477
externboolgistKeyIsEQ(GISTSTATE*giststate,intattno,Datuma,Datumb);
478478
externvoidgistDeCompressAtt(GISTSTATE*giststate,Relationr,IndexTupletuple,Pagep,
479479
OffsetNumbero,GISTENTRY*attdata,bool*isnull);
480-
externIndexTuplegistFetchTuple(GISTSTATE*giststate,Relationr,
480+
externHeapTuplegistFetchTuple(GISTSTATE*giststate,Relationr,
481481
IndexTupletuple);
482482
externvoidgistMakeUnionKey(GISTSTATE*giststate,intattno,
483483
GISTENTRY*entry1,boolisnull1,

‎src/include/access/relscan.h‎

Lines changed: 8 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -104,9 +104,16 @@ typedef struct IndexScanDescData
104104
/* index access method's private state */
105105
void*opaque;/* access-method-specific info */
106106

107-
/* in an index-only scan, this is valid after a successful amgettuple */
107+
/*
108+
* In an index-only scan, a successful amgettuple call must fill either
109+
* xs_itup (and xs_itupdesc) or xs_hitup (and xs_hitupdesc) to provide the
110+
* data returned by the scan. It can fill both, in which case the heap
111+
* format will be used.
112+
*/
108113
IndexTuplexs_itup;/* index tuple returned by AM */
109114
TupleDescxs_itupdesc;/* rowtype descriptor of xs_itup */
115+
HeapTuplexs_hitup;/* index data returned by AM, as HeapTuple */
116+
TupleDescxs_hitupdesc;/* rowtype descriptor of xs_hitup */
110117

111118
/* xs_ctup/xs_cbuf/xs_recheck are valid after a successful index_getnext */
112119
HeapTupleDataxs_ctup;/* current heap tuple, if any */

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