From 80b9e9c4664a020ebd14889046bd8d22a17d1ca6 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sun, 3 Mar 2019 16:57:14 -0500 Subject: [PATCH] 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 performance impact is already quite visible at ten columns. The obvious move is to replace that with a call to index_deform_tuple ... but that's *also* a loop over index_getattr. Improve it to be essentially a clone of heap_deform_tuple. (There are a few other places that loop over all index columns with index_getattr, and perhaps should be changed likewise, but most of them don't seem performance-critical. Anyway, the rest would mostly only be interested in the index key columns, which there aren't likely to be so many of. Wide index tuples are a new thing with INCLUDE.) Konstantin Knizhnik Discussion: https://postgr.es/m/e06b2d27-04fc-5c0e-bb8c-ecd72aa24959@postgrespro.ru --- src/backend/access/common/indextuple.c | 69 ++++++++++++++++++++++-- src/backend/executor/nodeIndexonlyscan.c | 20 +++---- 2 files changed, 72 insertions(+), 17 deletions(-) diff --git a/src/backend/access/common/indextuple.c b/src/backend/access/common/indextuple.c index 6a22b172036..32c0ebb93a4 100644 --- a/src/backend/access/common/indextuple.c +++ b/src/backend/access/common/indextuple.c @@ -418,19 +418,80 @@ nocache_index_getattr(IndexTuple tup, * * The caller must allocate sufficient storage for the output arrays. * (INDEX_MAX_KEYS entries should be enough.) + * + * This is nearly the same as heap_deform_tuple(), but for IndexTuples. + * One difference is that the tuple should never have any missing columns. */ void index_deform_tuple(IndexTuple tup, TupleDesc tupleDescriptor, Datum *values, bool *isnull) { - int i; + int hasnulls = IndexTupleHasNulls(tup); + int natts = tupleDescriptor->natts; /* number of atts to extract */ + int attnum; + char *tp; /* ptr to tuple data */ + int off; /* offset in tuple data */ + bits8 *bp; /* ptr to null bitmap in tuple */ + bool slow = false; /* can we use/set attcacheoff? */ /* Assert to protect callers who allocate fixed-size arrays */ - Assert(tupleDescriptor->natts <= INDEX_MAX_KEYS); + Assert(natts <= INDEX_MAX_KEYS); - for (i = 0; i < tupleDescriptor->natts; i++) + /* XXX "knows" t_bits are just after fixed tuple header! */ + bp = (bits8 *) ((char *) tup + sizeof(IndexTupleData)); + + tp = (char *) tup + IndexInfoFindDataOffset(tup->t_info); + off = 0; + + for (attnum = 0; attnum < natts; attnum++) { - values[i] = index_getattr(tup, i + 1, tupleDescriptor, &isnull[i]); + Form_pg_attribute thisatt = TupleDescAttr(tupleDescriptor, attnum); + + if (hasnulls && att_isnull(attnum, bp)) + { + values[attnum] = (Datum) 0; + isnull[attnum] = true; + slow = true; /* can't use attcacheoff anymore */ + continue; + } + + isnull[attnum] = false; + + if (!slow && thisatt->attcacheoff >= 0) + off = thisatt->attcacheoff; + else if (thisatt->attlen == -1) + { + /* + * We can only cache the offset for a varlena attribute if the + * offset is already suitably aligned, so that there would be no + * pad bytes in any case: then the offset will be valid for either + * an aligned or unaligned value. + */ + if (!slow && + off == att_align_nominal(off, thisatt->attalign)) + thisatt->attcacheoff = off; + else + { + off = att_align_pointer(off, thisatt->attalign, -1, + tp + off); + slow = true; + } + } + else + { + /* not varlena, so safe to use att_align_nominal */ + off = att_align_nominal(off, thisatt->attalign); + + if (!slow) + thisatt->attcacheoff = off; + } + + values[attnum] = fetchatt(thisatt, tp + off); + + off = att_addlength_pointer(off, thisatt->attlen, tp + off); + + if (thisatt->attlen <= 0) + slow = true; /* can't use attcacheoff anymore */ } } diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c index 72c04b528f5..26758e77039 100644 --- a/src/backend/executor/nodeIndexonlyscan.c +++ b/src/backend/executor/nodeIndexonlyscan.c @@ -269,23 +269,17 @@ IndexOnlyNext(IndexOnlyScanState *node) static void StoreIndexTuple(TupleTableSlot *slot, IndexTuple itup, TupleDesc itupdesc) { - int nindexatts = itupdesc->natts; - Datum *values = slot->tts_values; - bool *isnull = slot->tts_isnull; - int i; - /* - * Note: we must use the tupdesc supplied by the AM in index_getattr, not - * the slot's tupdesc, in case the latter has different datatypes (this - * happens for btree name_ops in particular). They'd better have the same - * number of columns though, as well as being datatype-compatible which is - * something we can't so easily check. + * Note: we must use the tupdesc supplied by the AM in index_deform_tuple, + * not the slot's tupdesc, in case the latter has different datatypes + * (this happens for btree name_ops in particular). They'd better have + * the same number of columns though, as well as being datatype-compatible + * which is something we can't so easily check. */ - Assert(slot->tts_tupleDescriptor->natts == nindexatts); + Assert(slot->tts_tupleDescriptor->natts == itupdesc->natts); ExecClearTuple(slot); - for (i = 0; i < nindexatts; i++) - values[i] = index_getattr(itup, i + 1, itupdesc, &isnull[i]); + index_deform_tuple(itup, itupdesc, slot->tts_values, slot->tts_isnull); ExecStoreVirtualTuple(slot); }