diff options
Diffstat (limited to 'src/backend/optimizer/path/costsize.c')
| -rw-r--r-- | src/backend/optimizer/path/costsize.c | 75 |
1 files changed, 62 insertions, 13 deletions
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index 2d241e774d0..422ef923222 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -54,7 +54,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.176 2007/01/22 01:35:20 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.177 2007/01/22 20:00:39 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -108,6 +108,9 @@ bool enable_mergejoin = true; bool enable_hashjoin = true; +static MergeScanSelCache *cached_scansel(PlannerInfo *root, + RestrictInfo *rinfo, + PathKey *pathkey); static bool cost_qual_eval_walker(Node *node, QualCost *total); static Selectivity approx_selectivity(PlannerInfo *root, List *quals, JoinType jointype); @@ -1349,9 +1352,9 @@ cost_mergejoin(MergePath *path, PlannerInfo *root) * (unless it's an outer join, in which case the outer side has to be * scanned all the way anyway). Estimate fraction of the left and right * inputs that will actually need to be scanned. We use only the first - * (most significant) merge clause for this purpose. - * - * XXX mergejoinscansel is a bit expensive, can we cache its results? + * (most significant) merge clause for this purpose. Since + * mergejoinscansel() is a fairly expensive computation, we cache the + * results in the merge clause RestrictInfo. */ if (mergeclauses && path->jpath.jointype != JOIN_FULL) { @@ -1360,8 +1363,7 @@ cost_mergejoin(MergePath *path, PlannerInfo *root) List *ipathkeys; PathKey *opathkey; PathKey *ipathkey; - Selectivity leftscansel, - rightscansel; + MergeScanSelCache *cache; /* Get the input pathkeys to determine the sort-order details */ opathkeys = outersortkeys ? outersortkeys : outer_path->pathkeys; @@ -1376,22 +1378,21 @@ cost_mergejoin(MergePath *path, PlannerInfo *root) opathkey->pk_nulls_first != ipathkey->pk_nulls_first) elog(ERROR, "left and right pathkeys do not match in mergejoin"); - mergejoinscansel(root, (Node *) firstclause->clause, - opathkey->pk_opfamily, opathkey->pk_strategy, - &leftscansel, &rightscansel); + /* Get the selectivity with caching */ + cache = cached_scansel(root, firstclause, opathkey); if (bms_is_subset(firstclause->left_relids, outer_path->parent->relids)) { /* left side of clause is outer */ - outerscansel = leftscansel; - innerscansel = rightscansel; + outerscansel = cache->leftscansel; + innerscansel = cache->rightscansel; } else { /* left side of clause is inner */ - outerscansel = rightscansel; - innerscansel = leftscansel; + outerscansel = cache->rightscansel; + innerscansel = cache->leftscansel; } if (path->jpath.jointype == JOIN_LEFT) outerscansel = 1.0; @@ -1494,6 +1495,54 @@ cost_mergejoin(MergePath *path, PlannerInfo *root) } /* + * run mergejoinscansel() with caching + */ +static MergeScanSelCache * +cached_scansel(PlannerInfo *root, RestrictInfo *rinfo, PathKey *pathkey) +{ + MergeScanSelCache *cache; + ListCell *lc; + Selectivity leftscansel, + rightscansel; + MemoryContext oldcontext; + + /* Do we have this result already? */ + foreach(lc, rinfo->scansel_cache) + { + cache = (MergeScanSelCache *) lfirst(lc); + if (cache->opfamily == pathkey->pk_opfamily && + cache->strategy == pathkey->pk_strategy && + cache->nulls_first == pathkey->pk_nulls_first) + return cache; + } + + /* Nope, do the computation */ + mergejoinscansel(root, + (Node *) rinfo->clause, + pathkey->pk_opfamily, + pathkey->pk_strategy, + pathkey->pk_nulls_first, + &leftscansel, + &rightscansel); + + /* Cache the result in suitably long-lived workspace */ + oldcontext = MemoryContextSwitchTo(root->planner_cxt); + + cache = (MergeScanSelCache *) palloc(sizeof(MergeScanSelCache)); + cache->opfamily = pathkey->pk_opfamily; + cache->strategy = pathkey->pk_strategy; + cache->nulls_first = pathkey->pk_nulls_first; + cache->leftscansel = leftscansel; + cache->rightscansel = rightscansel; + + rinfo->scansel_cache = lappend(rinfo->scansel_cache, cache); + + MemoryContextSwitchTo(oldcontext); + + return cache; +} + +/* * cost_hashjoin * Determines and returns the cost of joining two relations using the * hash join algorithm. |