From 7eaed8f1a059bed00dfd4625931ece475b9c3451 Mon Sep 17 00:00:00 2001 From: Lukas Fittl Date: Sat, 4 Mar 2023 15:44:29 -0800 Subject: [PATCH v1] Add Estimated Cache Hit Ratio for Memoize plan nodes in EXPLAIN Memoize can substantially reduce the costs of certain Nested Loops, but its hard to see this clearly, since the often significantly discounted rescan costs are not shown in EXPLAIN. To help understand Memoize's impact better, remember the calculated estimated cache hit ratio, and show it in EXPLAIN output. --- src/backend/commands/explain.c | 7 +++++++ src/backend/optimizer/path/costsize.c | 3 +++ src/backend/optimizer/plan/createplan.c | 10 +++++++--- src/backend/optimizer/util/pathnode.c | 5 +++++ src/include/nodes/pathnodes.h | 1 + src/include/nodes/plannodes.h | 3 +++ 6 files changed, 26 insertions(+), 3 deletions(-) diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c index e57bda7b62..58fda99a69 100644 --- a/src/backend/commands/explain.c +++ b/src/backend/commands/explain.c @@ -3167,6 +3167,8 @@ show_memoize_info(MemoizeState *mstate, List *ancestors, ExplainState *es) { ExplainPropertyText("Cache Key", keystr.data, es); ExplainPropertyText("Cache Mode", mstate->binary_mode ? "binary" : "logical", es); + if (es->costs) + ExplainPropertyFloat("Cache Hit Ratio Estimated", "", ((Memoize *) plan)->hit_ratio, 2, es); } else { @@ -3174,6 +3176,11 @@ show_memoize_info(MemoizeState *mstate, List *ancestors, ExplainState *es) appendStringInfo(es->str, "Cache Key: %s\n", keystr.data); ExplainIndentText(es); appendStringInfo(es->str, "Cache Mode: %s\n", mstate->binary_mode ? "binary" : "logical"); + if (es->costs) + { + ExplainIndentText(es); + appendStringInfo(es->str, "Cache Hit Ratio Estimated: %0.2f\n", ((Memoize *) plan)->hit_ratio); + } } pfree(keystr.data); diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index 7918bb6f0d..a0fd3f8965 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -2600,6 +2600,9 @@ cost_memoize_rescan(PlannerInfo *root, MemoizePath *mpath, */ startup_cost += cpu_tuple_cost; + /* Remember cache hit ratio for a potential EXPLAIN later */ + mpath->hit_ratio = hit_ratio; + *rescan_startup_cost = startup_cost; *rescan_total_cost = total_cost; } diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c index fa09a6103b..4c403cb081 100644 --- a/src/backend/optimizer/plan/createplan.c +++ b/src/backend/optimizer/plan/createplan.c @@ -280,7 +280,8 @@ static Material *make_material(Plan *lefttree); static Memoize *make_memoize(Plan *lefttree, Oid *hashoperators, Oid *collations, List *param_exprs, bool singlerow, bool binary_mode, - uint32 est_entries, Bitmapset *keyparamids); + uint32 est_entries, Bitmapset *keyparamids, + double hit_ratio); static WindowAgg *make_windowagg(List *tlist, Index winref, int partNumCols, AttrNumber *partColIdx, Oid *partOperators, Oid *partCollations, int ordNumCols, AttrNumber *ordColIdx, Oid *ordOperators, Oid *ordCollations, @@ -1691,7 +1692,8 @@ create_memoize_plan(PlannerInfo *root, MemoizePath *best_path, int flags) plan = make_memoize(subplan, operators, collations, param_exprs, best_path->singlerow, best_path->binary_mode, - best_path->est_entries, keyparamids); + best_path->est_entries, keyparamids, + best_path->hit_ratio); copy_generic_path_info(&plan->plan, (Path *) best_path); @@ -6528,7 +6530,8 @@ materialize_finished_plan(Plan *subplan) static Memoize * make_memoize(Plan *lefttree, Oid *hashoperators, Oid *collations, List *param_exprs, bool singlerow, bool binary_mode, - uint32 est_entries, Bitmapset *keyparamids) + uint32 est_entries, Bitmapset *keyparamids, + double hit_ratio) { Memoize *node = makeNode(Memoize); Plan *plan = &node->plan; @@ -6546,6 +6549,7 @@ make_memoize(Plan *lefttree, Oid *hashoperators, Oid *collations, node->binary_mode = binary_mode; node->est_entries = est_entries; node->keyparamids = keyparamids; + node->hit_ratio = hit_ratio; return node; } diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c index d749b50578..d4186784c5 100644 --- a/src/backend/optimizer/util/pathnode.c +++ b/src/backend/optimizer/util/pathnode.c @@ -1624,6 +1624,11 @@ create_memoize_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath, */ pathnode->est_entries = 0; + /* + * The estimated cache hit ratio will calculated later by cost_memoize_rescan() + */ + pathnode->hit_ratio = 0; + /* * Add a small additional charge for caching the first entry. All the * harder calculations for rescans are performed in cost_memoize_rescan(). diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h index d61a62da19..1b7cab3bc5 100644 --- a/src/include/nodes/pathnodes.h +++ b/src/include/nodes/pathnodes.h @@ -1962,6 +1962,7 @@ typedef struct MemoizePath uint32 est_entries; /* The maximum number of entries that the * planner expects will fit in the cache, or 0 * if unknown */ + double hit_ratio; /* Estimated cache hit ratio, kept for EXPLAIN */ } MemoizePath; /* diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h index 659bd05c0c..7966062a32 100644 --- a/src/include/nodes/plannodes.h +++ b/src/include/nodes/plannodes.h @@ -923,6 +923,9 @@ typedef struct Memoize /* paramids from param_exprs */ Bitmapset *keyparamids; + + /* Estimated cache hit ratio, kept for EXPLAIN */ + double hit_ratio; } Memoize; /* ---------------- -- 2.34.0