From 336c1d7a515b4d6de237679022d70082d7b69d9a Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sun, 16 Oct 2011 19:15:04 -0400 Subject: [PATCH] Avoid assuming that index-only scan data matches the index's rowtype. In general the data returned by an index-only scan should have the datatypes originally computed by FormIndexDatum. If the index opclasses use "storage" datatypes different from their input datatypes, the scan tuple will not have the same rowtype attributed to the index; but we had a hard-wired assumption that that was true in nodeIndexonlyscan.c. We'd already hacked around the issue for the one case where the types are different in btree indexes (btree name_ops), but this would definitely come back to bite us if we ever implement index-only scans in GiST. To fix, require the index AM to explicitly provide the tupdesc for the tuple it is returning. btree can just pass back the index's tupdesc, but GiST will have to work harder when and if it supports index-only scans. I had previously proposed fixing this by allowing the index AM to fill the scan tuple slot directly; but on reflection that seemed like a module layering violation, since TupleTableSlots are creatures of the executor. At least in the btree case, it would also be less efficient, since the tuple deconstruction work would occur even for rows later found to be invisible to the scan's snapshot. --- doc/src/sgml/indexam.sgml | 3 ++- src/backend/access/index/genam.c | 1 + src/backend/access/nbtree/nbtree.c | 5 ++++- src/backend/executor/nodeIndexonlyscan.c | 16 ++++++++-------- src/include/access/relscan.h | 2 ++ 5 files changed, 17 insertions(+), 10 deletions(-) diff --git a/doc/src/sgml/indexam.sgml b/doc/src/sgml/indexam.sgml index 80f55da87b..a6e4466e8a 100644 --- a/doc/src/sgml/indexam.sgml +++ b/doc/src/sgml/indexam.sgml @@ -396,7 +396,8 @@ amgettuple (IndexScanDesc scan, row), then on success it must also check scan->xs_want_itup, and if that is true it must return the original indexed data for the index entry, in the form of an - IndexTuple pointer stored at scan->xs_itup. + IndexTuple pointer stored at scan->xs_itup, + with tuple descriptor scan->xs_itupdesc. (Management of the data referenced by the pointer is the access method's responsibility. The data must remain good at least until the next amgettuple, amrescan, or amendscan diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c index 236e48912b..1732ef7bfe 100644 --- a/src/backend/access/index/genam.c +++ b/src/backend/access/index/genam.c @@ -112,6 +112,7 @@ RelationGetIndexScan(Relation indexRelation, int nkeys, int norderbys) scan->opaque = NULL; scan->xs_itup = NULL; + scan->xs_itupdesc = NULL; ItemPointerSetInvalid(&scan->xs_ctup.t_self); scan->xs_ctup.t_data = NULL; diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c index 60b7f599a7..f3a1d256a0 100644 --- a/src/backend/access/nbtree/nbtree.c +++ b/src/backend/access/nbtree/nbtree.c @@ -433,12 +433,15 @@ btbeginscan(PG_FUNCTION_ARGS) /* * We don't know yet whether the scan will be index-only, so we do not - * allocate the tuple workspace arrays until btrescan. + * allocate the tuple workspace arrays until btrescan. However, we set up + * scan->xs_itupdesc whether we'll need it or not, since that's so cheap. */ so->currTuples = so->markTuples = NULL; so->currPos.nextTupleOffset = 0; so->markPos.nextTupleOffset = 0; + scan->xs_itupdesc = RelationGetDescr(rel); + scan->opaque = so; PG_RETURN_POINTER(scan); diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c index e3742cf71d..a07686d463 100644 --- a/src/backend/executor/nodeIndexonlyscan.c +++ b/src/backend/executor/nodeIndexonlyscan.c @@ -36,7 +36,7 @@ static TupleTableSlot *IndexOnlyNext(IndexOnlyScanState *node); static void StoreIndexTuple(TupleTableSlot *slot, IndexTuple itup, - Relation indexRel); + TupleDesc itupdesc); /* ---------------------------------------------------------------- @@ -114,7 +114,7 @@ IndexOnlyNext(IndexOnlyScanState *node) /* * Fill the scan tuple slot with data from the index. */ - StoreIndexTuple(slot, scandesc->xs_itup, scandesc->indexRelation); + StoreIndexTuple(slot, scandesc->xs_itup, scandesc->xs_itupdesc); /* * If the index was lossy, we have to recheck the index quals. @@ -151,25 +151,25 @@ IndexOnlyNext(IndexOnlyScanState *node) * right now we don't need it elsewhere. */ static void -StoreIndexTuple(TupleTableSlot *slot, IndexTuple itup, Relation indexRel) +StoreIndexTuple(TupleTableSlot *slot, IndexTuple itup, TupleDesc itupdesc) { - TupleDesc indexDesc = RelationGetDescr(indexRel); - int nindexatts = indexDesc->natts; + int nindexatts = itupdesc->natts; Datum *values = slot->tts_values; bool *isnull = slot->tts_isnull; int i; /* - * Note: we must use the index relation's tupdesc in index_getattr, not + * 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. + * 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); ExecClearTuple(slot); for (i = 0; i < nindexatts; i++) - values[i] = index_getattr(itup, i + 1, indexDesc, &isnull[i]); + values[i] = index_getattr(itup, i + 1, itupdesc, &isnull[i]); ExecStoreVirtualTuple(slot); } diff --git a/src/include/access/relscan.h b/src/include/access/relscan.h index d48bbf865e..b2dea15a63 100644 --- a/src/include/access/relscan.h +++ b/src/include/access/relscan.h @@ -17,6 +17,7 @@ #include "access/genam.h" #include "access/heapam.h" #include "access/itup.h" +#include "access/tupdesc.h" typedef struct HeapScanDescData @@ -80,6 +81,7 @@ typedef struct IndexScanDescData /* in an index-only scan, this is valid after a successful amgettuple */ IndexTuple xs_itup; /* index tuple returned by AM */ + TupleDesc xs_itupdesc; /* rowtype descriptor of xs_itup */ /* xs_ctup/xs_cbuf/xs_recheck are valid after a successful index_getnext */ HeapTupleData xs_ctup; /* current heap tuple, if any */