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Rearrange the implementation of index-only scans.

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This commit changes index-only scans so that data is read directly from the
index tuple without first generating a faux heap tuple.  The only immediate
benefit is that indexes on system columns (such as OID) can be used in
index-only scans, but this is necessary infrastructure if we are ever to
support index-only scans on expression indexes.  The executor is now ready
for that, though the planner still needs substantial work to recognize
the possibility.

To do this, Vars in index-only plan nodes have to refer to index columns
not heap columns.  I introduced a new special varno, INDEX_VAR, to mark
such Vars to avoid confusion.  (In passing, this commit renames the two
existing special varnos to OUTER_VAR and INNER_VAR.)  This allows
ruleutils.c to handle them with logic similar to what we use for subplan
reference Vars.

Since index-only scans are now fundamentally different from regular
indexscans so far as their expression subtrees are concerned, I also chose
to change them to have their own plan node type (and hence, their own
executor source file).
This commit is contained in:
Tom Lane
2011-10-11 14:20:06 -04:00
parent fa351d5a0d
commit a0185461dd
34 changed files with 1312 additions and 419 deletions
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36
src/include/nodes/execnodes.h
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@ -1226,7 +1226,6 @@ typedef struct
* RuntimeContext expr context for evaling runtime Skeys
* RelationDesc index relation descriptor
* ScanDesc index scan descriptor
* VMBuffer buffer in use for visibility map testing, if any
* ----------------
*/
typedef struct IndexScanState
@ -1243,9 +1242,42 @@ typedef struct IndexScanState
ExprContext *iss_RuntimeContext;
Relation iss_RelationDesc;
IndexScanDesc iss_ScanDesc;
Buffer iss_VMBuffer;
} IndexScanState;
/* ----------------
* IndexOnlyScanState information
*
* indexqual execution state for indexqual expressions
* ScanKeys Skey structures for index quals
* NumScanKeys number of ScanKeys
* OrderByKeys Skey structures for index ordering operators
* NumOrderByKeys number of OrderByKeys
* RuntimeKeys info about Skeys that must be evaluated at runtime
* NumRuntimeKeys number of RuntimeKeys
* RuntimeKeysReady true if runtime Skeys have been computed
* RuntimeContext expr context for evaling runtime Skeys
* RelationDesc index relation descriptor
* ScanDesc index scan descriptor
* VMBuffer buffer in use for visibility map testing, if any
* ----------------
*/
typedef struct IndexOnlyScanState
{
ScanState ss; /* its first field is NodeTag */
List *indexqual;
ScanKey ioss_ScanKeys;
int ioss_NumScanKeys;
ScanKey ioss_OrderByKeys;
int ioss_NumOrderByKeys;
IndexRuntimeKeyInfo *ioss_RuntimeKeys;
int ioss_NumRuntimeKeys;
bool ioss_RuntimeKeysReady;
ExprContext *ioss_RuntimeContext;
Relation ioss_RelationDesc;
IndexScanDesc ioss_ScanDesc;
Buffer ioss_VMBuffer;
} IndexOnlyScanState;
/* ----------------
* BitmapIndexScanState information
*