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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
View File

@ -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 =

68
src/backend/optimizer/path/pathkeys.c
View File

@ -25,7 +25,6 @@
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/tlist.h"
#include "parser/parsetree.h"
#include "utils/lsyscache.h"
@ -35,8 +34,6 @@ static PathKey *make_canonical_pathkey(PlannerInfo *root,
EquivalenceClass *eclass, Oid opfamily,
int strategy, bool nulls_first);
static bool pathkey_is_redundant(PathKey *new_pathkey, List *pathkeys);
static Var *find_indexkey_var(PlannerInfo *root, RelOptInfo *rel,
AttrNumber varattno);
static bool right_merge_direction(PlannerInfo *root, PathKey *pathkey);
@ -504,21 +501,24 @@ build_index_pathkeys(PlannerInfo *root,
ScanDirection scandir)
{
List *retval = NIL;
ListCell *indexprs_item;
ListCell *lc;
int i;
if (index->sortopfamily == NULL)
return NIL; /* non-orderable index */
indexprs_item = list_head(index->indexprs);
for (i = 0; i < index->ncolumns; i++)
i = 0;
foreach(lc, index->indextlist)
{
TargetEntry *indextle = (TargetEntry *) lfirst(lc);
Expr *indexkey;
bool reverse_sort;
bool nulls_first;
int ikey;
Expr *indexkey;
PathKey *cpathkey;
/* We assume we don't need to make a copy of the tlist item */
indexkey = indextle->expr;
if (ScanDirectionIsBackward(scandir))
{
reverse_sort = !index->reverse_sort[i];
@ -530,21 +530,6 @@ build_index_pathkeys(PlannerInfo *root,
nulls_first = index->nulls_first[i];
}
ikey = index->indexkeys[i];
if (ikey != 0)
{
/* simple index column */
indexkey = (Expr *) find_indexkey_var(root, index->rel, ikey);
}
else
{
/* expression --- assume we need not copy it */
if (indexprs_item == NULL)
elog(ERROR, "wrong number of index expressions");
indexkey = (Expr *) lfirst(indexprs_item);
indexprs_item = lnext(indexprs_item);
}
/* OK, try to make a canonical pathkey for this sort key */
cpathkey = make_pathkey_from_sortinfo(root,
indexkey,
@ -568,46 +553,13 @@ build_index_pathkeys(PlannerInfo *root,
/* Add to list unless redundant */
if (!pathkey_is_redundant(cpathkey, retval))
retval = lappend(retval, cpathkey);
i++;
}
return retval;
}
/*
* Find or make a Var node for the specified attribute of the rel.
*
* We first look for the var in the rel's target list, because that's
* easy and fast. But the var might not be there (this should normally
* only happen for vars that are used in WHERE restriction clauses,
* but not in join clauses or in the SELECT target list). In that case,
* gin up a Var node the hard way.
*/
static Var *
find_indexkey_var(PlannerInfo *root, RelOptInfo *rel, AttrNumber varattno)
{
ListCell *temp;
Index relid;
Oid reloid,
vartypeid,
varcollid;
int32 type_mod;
foreach(temp, rel->reltargetlist)
{
Var *var = (Var *) lfirst(temp);
if (IsA(var, Var) &&
var->varattno == varattno)
return var;
}
relid = rel->relid;
reloid = getrelid(relid, root->parse->rtable);
get_atttypetypmodcoll(reloid, varattno, &vartypeid, &type_mod, &varcollid);
return makeVar(relid, varattno, vartypeid, type_mod, varcollid, 0);
}
/*
* convert_subquery_pathkeys
* Build a pathkeys list that describes the ordering of a subquery's