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Rearrange the implementation of index-only scans.
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).
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@@ -26,6 +26,7 @@
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#include "executor/nodeGroup.h"
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#include "executor/nodeHash.h"
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#include "executor/nodeHashjoin.h"
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#include "executor/nodeIndexonlyscan.h"
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#include "executor/nodeIndexscan.h"
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#include "executor/nodeLimit.h"
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#include "executor/nodeLockRows.h"
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@@ -155,6 +156,10 @@ ExecReScan(PlanState *node)
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ExecReScanIndexScan((IndexScanState *) node);
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break;
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case T_IndexOnlyScanState:
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ExecReScanIndexOnlyScan((IndexOnlyScanState *) node);
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break;
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case T_BitmapIndexScanState:
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ExecReScanBitmapIndexScan((BitmapIndexScanState *) node);
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break;
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@@ -273,6 +278,10 @@ ExecMarkPos(PlanState *node)
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ExecIndexMarkPos((IndexScanState *) node);
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break;
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case T_IndexOnlyScanState:
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ExecIndexOnlyMarkPos((IndexOnlyScanState *) node);
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break;
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case T_TidScanState:
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ExecTidMarkPos((TidScanState *) node);
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break;
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@@ -326,6 +335,10 @@ ExecRestrPos(PlanState *node)
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ExecIndexRestrPos((IndexScanState *) node);
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break;
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case T_IndexOnlyScanState:
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ExecIndexOnlyRestrPos((IndexOnlyScanState *) node);
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break;
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case T_TidScanState:
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ExecTidRestrPos((TidScanState *) node);
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break;
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@@ -371,6 +384,7 @@ ExecSupportsMarkRestore(NodeTag plantype)
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{
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case T_SeqScan:
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case T_IndexScan:
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case T_IndexOnlyScan:
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case T_TidScan:
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case T_ValuesScan:
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case T_Material:
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@@ -442,6 +456,10 @@ ExecSupportsBackwardScan(Plan *node)
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return IndexSupportsBackwardScan(((IndexScan *) node)->indexid) &&
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TargetListSupportsBackwardScan(node->targetlist);
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case T_IndexOnlyScan:
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return IndexSupportsBackwardScan(((IndexOnlyScan *) node)->indexid) &&
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TargetListSupportsBackwardScan(node->targetlist);
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case T_SubqueryScan:
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return ExecSupportsBackwardScan(((SubqueryScan *) node)->subplan) &&
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TargetListSupportsBackwardScan(node->targetlist);
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@@ -474,7 +492,8 @@ TargetListSupportsBackwardScan(List *targetlist)
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}
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/*
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* An IndexScan node supports backward scan only if the index's AM does.
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* An IndexScan or IndexOnlyScan node supports backward scan only if the
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* index's AM does.
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*/
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static bool
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IndexSupportsBackwardScan(Oid indexid)
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