diff options
Diffstat (limited to 'src/backend/optimizer/plan/createplan.c')
| -rw-r--r-- | src/backend/optimizer/plan/createplan.c | 40 |
1 files changed, 39 insertions, 1 deletions
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c index 4109ab25364..7d4a34b4f4b 100644 --- a/src/backend/optimizer/plan/createplan.c +++ b/src/backend/optimizer/plan/createplan.c @@ -10,7 +10,7 @@ * * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/createplan.c,v 1.90 2000/05/23 16:56:36 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/createplan.c,v 1.90.2.1 2000/09/08 02:11:33 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -639,6 +639,44 @@ create_mergejoin_node(MergePath *best_path, best_path->innersortkeys, inner_node); + /* + * The executor requires the inner side of a mergejoin to support "mark" + * and "restore" operations. Not all plan types do, so we must be careful + * not to generate an invalid plan. If necessary, an invalid inner plan + * can be handled by inserting a Materialize node. + * + * Since the inner side must be ordered, and only Sorts and IndexScans can + * create order to begin with, you might think there's no problem --- but + * you'd be wrong. Nestloop and merge joins can *preserve* the order of + * their inputs, so they can be selected as the input of a mergejoin, + * and that won't work in the present executor. + * + * Doing this here is a bit of a kluge since the cost of the Materialize + * wasn't taken into account in our earlier decisions. But Materialize + * is hard to estimate a cost for, and the above consideration shows that + * this is a rare case anyway, so this seems an acceptable way to proceed. + * + * This check must agree with ExecMarkPos/ExecRestrPos in + * executor/execAmi.c! + */ + switch (nodeTag(inner_node)) + { + case T_SeqScan: + case T_IndexScan: + case T_Material: + case T_Sort: + /* OK, these inner plans support mark/restore */ + break; + + default: + /* Ooops, need to materialize the inner plan */ + inner_node = (Plan *) make_material(inner_tlist, + _NONAME_RELATION_ID_, + inner_node, + 0); + break; + } + join_node = make_mergejoin(tlist, qpqual, mergeclauses, |