diff options
Diffstat (limited to 'src/backend/optimizer/plan/planmain.c')
| -rw-r--r-- | src/backend/optimizer/plan/planmain.c | 103 |
1 files changed, 65 insertions, 38 deletions
diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c index fc97a1bb507..f9f4b12db71 100644 --- a/src/backend/optimizer/plan/planmain.c +++ b/src/backend/optimizer/plan/planmain.c @@ -61,44 +61,6 @@ query_planner(PlannerInfo *root, List *tlist, RelOptInfo *final_rel; /* - * If the query has an empty join tree, then it's something easy like - * "SELECT 2+2;" or "INSERT ... VALUES()". Fall through quickly. - */ - if (parse->jointree->fromlist == NIL) - { - /* We need a dummy joinrel to describe the empty set of baserels */ - final_rel = build_empty_join_rel(root); - - /* - * If query allows parallelism in general, check whether the quals are - * parallel-restricted. (We need not check final_rel->reltarget - * because it's empty at this point. Anything parallel-restricted in - * the query tlist will be dealt with later.) - */ - if (root->glob->parallelModeOK) - final_rel->consider_parallel = - is_parallel_safe(root, parse->jointree->quals); - - /* The only path for it is a trivial Result path */ - add_path(final_rel, (Path *) - create_result_path(root, final_rel, - final_rel->reltarget, - (List *) parse->jointree->quals)); - - /* Select cheapest path (pretty easy in this case...) */ - set_cheapest(final_rel); - - /* - * We still are required to call qp_callback, in case it's something - * like "SELECT 2+2 ORDER BY 1". - */ - root->canon_pathkeys = NIL; - (*qp_callback) (root, qp_extra); - - return final_rel; - } - - /* * Init planner lists to empty. * * NOTE: append_rel_list was set up by subquery_planner, so do not touch @@ -125,6 +87,71 @@ query_planner(PlannerInfo *root, List *tlist, setup_simple_rel_arrays(root); /* + * In the trivial case where the jointree is a single RTE_RESULT relation, + * bypass all the rest of this function and just make a RelOptInfo and its + * one access path. This is worth optimizing because it applies for + * common cases like "SELECT expression" and "INSERT ... VALUES()". + */ + Assert(parse->jointree->fromlist != NIL); + if (list_length(parse->jointree->fromlist) == 1) + { + Node *jtnode = (Node *) linitial(parse->jointree->fromlist); + + if (IsA(jtnode, RangeTblRef)) + { + int varno = ((RangeTblRef *) jtnode)->rtindex; + RangeTblEntry *rte = root->simple_rte_array[varno]; + + Assert(rte != NULL); + if (rte->rtekind == RTE_RESULT) + { + /* Make the RelOptInfo for it directly */ + final_rel = build_simple_rel(root, varno, NULL); + + /* + * If query allows parallelism in general, check whether the + * quals are parallel-restricted. (We need not check + * final_rel->reltarget because it's empty at this point. + * Anything parallel-restricted in the query tlist will be + * dealt with later.) This is normally pretty silly, because + * a Result-only plan would never be interesting to + * parallelize. However, if force_parallel_mode is on, then + * we want to execute the Result in a parallel worker if + * possible, so we must do this. + */ + if (root->glob->parallelModeOK && + force_parallel_mode != FORCE_PARALLEL_OFF) + final_rel->consider_parallel = + is_parallel_safe(root, parse->jointree->quals); + + /* + * The only path for it is a trivial Result path. We cheat a + * bit here by using a GroupResultPath, because that way we + * can just jam the quals into it without preprocessing them. + * (But, if you hold your head at the right angle, a FROM-less + * SELECT is a kind of degenerate-grouping case, so it's not + * that much of a cheat.) + */ + add_path(final_rel, (Path *) + create_group_result_path(root, final_rel, + final_rel->reltarget, + (List *) parse->jointree->quals)); + + /* Select cheapest path (pretty easy in this case...) */ + set_cheapest(final_rel); + + /* + * We still are required to call qp_callback, in case it's + * something like "SELECT 2+2 ORDER BY 1". + */ + (*qp_callback) (root, qp_extra); + + return final_rel; + } + } + } + + /* * Populate append_rel_array with each AppendRelInfo to allow direct * lookups by child relid. */ |