From 8635a22ee5f90297756f072199c69a318bd17ea2 Mon Sep 17 00:00:00 2001 From: Ronan Dunklau Date: Mon, 12 Sep 2022 15:40:18 +0200 Subject: [PATCH v2] Fix gin costing. GIN index scans were not taking any descent CPU-based cost into account. That made them look cheaper than other types of indexes when they shouldn't be. We use the same heuristic as for btree indexes, but multiplying it by the number of searched entries. Per report of Hung Nguyen. --- src/backend/utils/adt/selfuncs.c | 34 +++++++++++++++++++++++++++++--- 1 file changed, 31 insertions(+), 3 deletions(-) diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index c746759eef..881e470a07 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -7419,6 +7419,7 @@ gincostestimate(PlannerInfo *root, IndexPath *path, double loop_count, qual_arg_cost, spc_random_page_cost, outer_scans; + Cost descentCost; Relation indexRel; GinStatsData ginStats; ListCell *lc; @@ -7622,7 +7623,7 @@ gincostestimate(PlannerInfo *root, IndexPath *path, double loop_count, * searches in entry tree, including search of first entry in partial * match algorithm */ - entryPagesFetched += ceil(counts.searchEntries * rint(pow(numEntryPages, 0.15))); + entryPagesFetched += ceil(counts.searchEntries * ceil(pow(numEntryPages, 0.15))); /* * Add an estimate of entry pages read by partial match algorithm. It's a @@ -7643,6 +7644,33 @@ gincostestimate(PlannerInfo *root, IndexPath *path, double loop_count, */ dataPagesFetched = ceil(numDataPages * partialScale); + *indexStartupCost = 0; + *indexTotalCost = 0; + + /* + * Add a CPU-cost component to represent the costs of initial entry btree + * descent. We don't charge any I/O cost for touching upper btree levels, + * since they tend to stay in cache, but we still have to do about log2(N) + * comparisons to descend a btree of N leaf tuples. We charge one + * cpu_operator_cost per comparison. + * + * If there are ScalarArrayOpExprs, charge this once per SA scan. The + * ones after the first one are not startup cost so far as the overall + * plan is concerned, so add them only to "total" cost. + */ + if (numEntries > 1) /* avoid computing log(0) */ + { + descentCost = ceil(log(numEntries) / log(2.0)) * cpu_operator_cost; + *indexStartupCost += descentCost * counts.searchEntries; + *indexTotalCost += counts.arrayScans * descentCost * counts.searchEntries; + } + + /* + * Add a cpu cost per page fetched. This is not amortized over a loop. + */ + *indexStartupCost += entryPagesFetched * 50.0 * cpu_operator_cost; + *indexTotalCost += entryPagesFetched * counts.arrayScans * 50.0 * cpu_operator_cost; + /* * Calculate cache effects if more than one scan due to nestloops or array * quals. The result is pro-rated per nestloop scan, but the array qual @@ -7666,7 +7694,7 @@ gincostestimate(PlannerInfo *root, IndexPath *path, double loop_count, * Here we use random page cost because logically-close pages could be far * apart on disk. */ - *indexStartupCost = (entryPagesFetched + dataPagesFetched) * spc_random_page_cost; + *indexStartupCost += (entryPagesFetched + dataPagesFetched) * spc_random_page_cost; /* * Now compute the number of data pages fetched during the scan. @@ -7705,7 +7733,7 @@ gincostestimate(PlannerInfo *root, IndexPath *path, double loop_count, } /* And apply random_page_cost as the cost per page */ - *indexTotalCost = *indexStartupCost + + *indexTotalCost += *indexStartupCost + dataPagesFetched * spc_random_page_cost; /* -- 2.37.3