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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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23
src/backend/optimizer/path/indxpath.c
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@ -199,14 +199,15 @@ create_index_paths(PlannerInfo *root, RelOptInfo *rel)
true, NULL, SAOP_FORBID, ST_ANYSCAN);
/*
* Submit all the ones that can form plain IndexScan plans to add_path. (A
* plain IndexPath always represents a plain IndexScan plan; however some
* of the indexes might support only bitmap scans, and those we mustn't
* submit to add_path here.) Also, pick out the ones that might be useful
* as bitmap scans. For that, we must discard indexes that don't support
* bitmap scans, and we also are only interested in paths that have some
* selectivity; we should discard anything that was generated solely for
* ordering purposes.
* Submit all the ones that can form plain IndexScan plans to add_path.
* (A plain IndexPath might represent either a plain IndexScan or an
* IndexOnlyScan, but for our purposes here the distinction does not
* matter. However, some of the indexes might support only bitmap scans,
* and those we mustn't submit to add_path here.) Also, pick out the ones
* that might be useful as bitmap scans. For that, we must discard
* indexes that don't support bitmap scans, and we also are only
* interested in paths that have some selectivity; we should discard
* anything that was generated solely for ordering purposes.
*/
bitindexpaths = NIL;
foreach(l, indexpaths)
@ -1107,11 +1108,9 @@ check_index_only(RelOptInfo *rel, IndexOptInfo *index)
/*
* For the moment, we just ignore index expressions. It might be nice
* to do something with them, later. We also ignore index columns
* that are system columns (such as OID), because the virtual-tuple
* coding used by IndexStoreHeapTuple() can't deal with them.
* to do something with them, later.
*/
if (attno <= 0)
if (attno == 0)
continue;
index_attrs =