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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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@ -447,7 +447,20 @@ _outIndexScan(StringInfo str, IndexScan *node)
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WRITE_NODE_FIELD(indexorderby);
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WRITE_NODE_FIELD(indexorderbyorig);
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WRITE_ENUM_FIELD(indexorderdir, ScanDirection);
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WRITE_BOOL_FIELD(indexonly);
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}
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static void
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_outIndexOnlyScan(StringInfo str, IndexOnlyScan *node)
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{
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WRITE_NODE_TYPE("INDEXONLYSCAN");
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_outScanInfo(str, (Scan *) node);
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WRITE_OID_FIELD(indexid);
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WRITE_NODE_FIELD(indexqual);
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WRITE_NODE_FIELD(indexorderby);
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WRITE_NODE_FIELD(indextlist);
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WRITE_ENUM_FIELD(indexorderdir, ScanDirection);
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}
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static void
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@ -1501,7 +1514,6 @@ _outIndexPath(StringInfo str, IndexPath *node)
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WRITE_NODE_FIELD(indexorderbys);
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WRITE_BOOL_FIELD(isjoininner);
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WRITE_ENUM_FIELD(indexscandir, ScanDirection);
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WRITE_BOOL_FIELD(indexonly);
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WRITE_FLOAT_FIELD(indextotalcost, "%.2f");
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WRITE_FLOAT_FIELD(indexselectivity, "%.4f");
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WRITE_FLOAT_FIELD(rows, "%.0f");
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@ -1752,8 +1764,9 @@ _outIndexOptInfo(StringInfo str, IndexOptInfo *node)
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WRITE_FLOAT_FIELD(tuples, "%.0f");
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WRITE_INT_FIELD(ncolumns);
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WRITE_OID_FIELD(relam);
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WRITE_NODE_FIELD(indexprs);
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/* indexprs is redundant since we print indextlist */
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WRITE_NODE_FIELD(indpred);
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WRITE_NODE_FIELD(indextlist);
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WRITE_BOOL_FIELD(predOK);
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WRITE_BOOL_FIELD(unique);
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WRITE_BOOL_FIELD(hypothetical);
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@ -2707,6 +2720,9 @@ _outNode(StringInfo str, void *obj)
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case T_IndexScan:
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_outIndexScan(str, obj);
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break;
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case T_IndexOnlyScan:
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_outIndexOnlyScan(str, obj);
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break;
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case T_BitmapIndexScan:
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_outBitmapIndexScan(str, obj);
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break;
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