Fix confusion on different kinds of slots in IndexOnlyScans.
We used the same slot to store a tuple from the index, and to store a tuple from the table. That's not OK. It worked with the heap, because heapam_getnextslot() stores a HeapTuple to the slot, and doesn't care how large the tts_values/nulls arrays are. But when I played with a toy table AM implementation that used a virtual tuple, it caused memory overruns. In the passing, tidy up comments on the ioss_PscanLen fields.
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@ -166,10 +166,10 @@ IndexOnlyNext(IndexOnlyScanState *node)
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* Rats, we have to visit the heap to check visibility.
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*/
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InstrCountTuples2(node, 1);
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if (!index_fetch_heap(scandesc, slot))
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if (!index_fetch_heap(scandesc, node->ioss_TableSlot))
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continue; /* no visible tuple, try next index entry */
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ExecClearTuple(slot);
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ExecClearTuple(node->ioss_TableSlot);
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/*
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* Only MVCC snapshots are supported here, so there should be no
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@ -528,7 +528,17 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
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*/
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tupDesc = ExecTypeFromTL(node->indextlist);
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ExecInitScanTupleSlot(estate, &indexstate->ss, tupDesc,
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table_slot_callbacks(currentRelation));
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&TTSOpsVirtual);
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/*
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* We need another slot, in a format that's suitable for the table AM,
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* for when we need to fetch a tuple from the table for rechecking
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* visibility.
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*/
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indexstate->ioss_TableSlot =
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ExecAllocTableSlot(&estate->es_tupleTable,
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RelationGetDescr(currentRelation),
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table_slot_callbacks(currentRelation));
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/*
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* Initialize result type and projection info. The node's targetlist will
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@ -1359,7 +1359,7 @@ typedef struct
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* SortSupport for reordering ORDER BY exprs
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* OrderByTypByVals is the datatype of order by expression pass-by-value?
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* OrderByTypLens typlens of the datatypes of order by expressions
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* pscan_len size of parallel index scan descriptor
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* PscanLen size of parallel index scan descriptor
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* ----------------
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*/
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typedef struct IndexScanState
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@ -1403,8 +1403,9 @@ typedef struct IndexScanState
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* RuntimeContext expr context for evaling runtime Skeys
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* RelationDesc index relation descriptor
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* ScanDesc index scan descriptor
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* TableSlot slot for holding tuples fetched from the table
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* VMBuffer buffer in use for visibility map testing, if any
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* ioss_PscanLen Size of parallel index-only scan descriptor
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* PscanLen size of parallel index-only scan descriptor
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* ----------------
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*/
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typedef struct IndexOnlyScanState
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@ -1421,6 +1422,7 @@ typedef struct IndexOnlyScanState
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ExprContext *ioss_RuntimeContext;
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Relation ioss_RelationDesc;
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struct IndexScanDescData *ioss_ScanDesc;
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TupleTableSlot *ioss_TableSlot;
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Buffer ioss_VMBuffer;
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Size ioss_PscanLen;
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} IndexOnlyScanState;
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