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Commit80b9e9c

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Improve performance of index-only scans with many index columns.
StoreIndexTuple was a loop over index_getattr, which is O(N^2)if the index columns are variable-width, and the performanceimpact is already quite visible at ten columns. The obviousmove is to replace that with a call to index_deform_tuple ...but that's *also* a loop over index_getattr. Improve it tobe essentially a clone of heap_deform_tuple.(There are a few other places that loop over all index columnswith index_getattr, and perhaps should be changed likewise,but most of them don't seem performance-critical. Anyway, therest would mostly only be interested in the index key columns,which there aren't likely to be so many of. Wide index tuplesare a new thing with INCLUDE.)Konstantin KnizhnikDiscussion:https://postgr.es/m/e06b2d27-04fc-5c0e-bb8c-ecd72aa24959@postgrespro.ru
1 parent78b408a commit80b9e9c

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2 files changed

+72
-17
lines changed

2 files changed

+72
-17
lines changed

‎src/backend/access/common/indextuple.c

Lines changed: 65 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -418,19 +418,80 @@ nocache_index_getattr(IndexTuple tup,
418418
*
419419
* The caller must allocate sufficient storage for the output arrays.
420420
* (INDEX_MAX_KEYS entries should be enough.)
421+
*
422+
* This is nearly the same as heap_deform_tuple(), but for IndexTuples.
423+
* One difference is that the tuple should never have any missing columns.
421424
*/
422425
void
423426
index_deform_tuple(IndexTupletup,TupleDesctupleDescriptor,
424427
Datum*values,bool*isnull)
425428
{
426-
inti;
429+
inthasnulls=IndexTupleHasNulls(tup);
430+
intnatts=tupleDescriptor->natts;/* number of atts to extract */
431+
intattnum;
432+
char*tp;/* ptr to tuple data */
433+
intoff;/* offset in tuple data */
434+
bits8*bp;/* ptr to null bitmap in tuple */
435+
boolslow= false;/* can we use/set attcacheoff? */
427436

428437
/* Assert to protect callers who allocate fixed-size arrays */
429-
Assert(tupleDescriptor->natts <=INDEX_MAX_KEYS);
438+
Assert(natts <=INDEX_MAX_KEYS);
439+
440+
/* XXX "knows" t_bits are just after fixed tuple header! */
441+
bp= (bits8*) ((char*)tup+sizeof(IndexTupleData));
430442

431-
for (i=0;i<tupleDescriptor->natts;i++)
443+
tp= (char*)tup+IndexInfoFindDataOffset(tup->t_info);
444+
off=0;
445+
446+
for (attnum=0;attnum<natts;attnum++)
432447
{
433-
values[i]=index_getattr(tup,i+1,tupleDescriptor,&isnull[i]);
448+
Form_pg_attributethisatt=TupleDescAttr(tupleDescriptor,attnum);
449+
450+
if (hasnulls&&att_isnull(attnum,bp))
451+
{
452+
values[attnum]= (Datum)0;
453+
isnull[attnum]= true;
454+
slow= true;/* can't use attcacheoff anymore */
455+
continue;
456+
}
457+
458+
isnull[attnum]= false;
459+
460+
if (!slow&&thisatt->attcacheoff >=0)
461+
off=thisatt->attcacheoff;
462+
elseif (thisatt->attlen==-1)
463+
{
464+
/*
465+
* We can only cache the offset for a varlena attribute if the
466+
* offset is already suitably aligned, so that there would be no
467+
* pad bytes in any case: then the offset will be valid for either
468+
* an aligned or unaligned value.
469+
*/
470+
if (!slow&&
471+
off==att_align_nominal(off,thisatt->attalign))
472+
thisatt->attcacheoff=off;
473+
else
474+
{
475+
off=att_align_pointer(off,thisatt->attalign,-1,
476+
tp+off);
477+
slow= true;
478+
}
479+
}
480+
else
481+
{
482+
/* not varlena, so safe to use att_align_nominal */
483+
off=att_align_nominal(off,thisatt->attalign);
484+
485+
if (!slow)
486+
thisatt->attcacheoff=off;
487+
}
488+
489+
values[attnum]=fetchatt(thisatt,tp+off);
490+
491+
off=att_addlength_pointer(off,thisatt->attlen,tp+off);
492+
493+
if (thisatt->attlen <=0)
494+
slow= true;/* can't use attcacheoff anymore */
434495
}
435496
}
436497

‎src/backend/executor/nodeIndexonlyscan.c

Lines changed: 7 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -269,23 +269,17 @@ IndexOnlyNext(IndexOnlyScanState *node)
269269
staticvoid
270270
StoreIndexTuple(TupleTableSlot*slot,IndexTupleitup,TupleDescitupdesc)
271271
{
272-
intnindexatts=itupdesc->natts;
273-
Datum*values=slot->tts_values;
274-
bool*isnull=slot->tts_isnull;
275-
inti;
276-
277272
/*
278-
* Note: we must use the tupdesc supplied by the AM inindex_getattr, not
279-
* the slot's tupdesc, in case the latter has different datatypes (this
280-
* happens for btree name_ops in particular). They'd better have the same
281-
* number of columns though, as well as being datatype-compatible which is
282-
* something we can't so easily check.
273+
* Note: we must use the tupdesc supplied by the AM inindex_deform_tuple,
274+
*notthe slot's tupdesc, in case the latter has different datatypes
275+
*(thishappens for btree name_ops in particular). They'd better have
276+
*the samenumber of columns though, as well as being datatype-compatible
277+
*which issomething we can't so easily check.
283278
*/
284-
Assert(slot->tts_tupleDescriptor->natts==nindexatts);
279+
Assert(slot->tts_tupleDescriptor->natts==itupdesc->natts);
285280

286281
ExecClearTuple(slot);
287-
for (i=0;i<nindexatts;i++)
288-
values[i]=index_getattr(itup,i+1,itupdesc,&isnull[i]);
282+
index_deform_tuple(itup,itupdesc,slot->tts_values,slot->tts_isnull);
289283
ExecStoreVirtualTuple(slot);
290284
}
291285

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