Flush Memoize cache when non-key parameters change

It's possible that a subplan below a Memoize node contains a parameter
from above the Memoize node.  If this parameter changes then cache entries
may become out-dated due to the new parameter value.

Previously Memoize was mistakenly not aware of this.  We fix this here by
flushing the cache whenever a parameter that's not part of the cache
key changes.

Bug: #17213
Reported by: Elvis Pranskevichus
Author: David Rowley
Discussion: https://postgr.es/m/17213-988ed34b225a2862@postgresql.org
Backpatch-through: 14, where Memoize was added

diff --git a/src/backend/executor/nodeMemoize.c b/src/backend/executor/nodeMemoize.c
index 683502dd90e1b6f4444712725c454d599e65c602..31e39722239da1e16e88f8dfc910e4a63f765698 100644 (file)
--- a/src/backend/executor/nodeMemoize.c
+++ b/src/backend/executor/nodeMemoize.c
@@ -367,6 +367,37 @@ remove_cache_entry(MemoizeState *mstate, MemoizeEntry *entry)
        pfree(key);
 }
 
+/*
+ * cache_purge_all
+ *             Remove all items from the cache
+ */
+static void
+cache_purge_all(MemoizeState *mstate)
+{
+       uint64          evictions = mstate->hashtable->members;
+       PlanState *pstate = (PlanState *) mstate;
+
+       /*
+        * Likely the most efficient way to remove all items is to just reset the
+        * memory context for the cache and then rebuild a fresh hash table.  This
+        * saves having to remove each item one by one and pfree each cached tuple
+        */
+       MemoryContextReset(mstate->tableContext);
+
+       /* Make the hash table the same size as the original size */
+       build_hash_table(mstate, ((Memoize *) pstate->plan)->est_entries);
+
+       /* reset the LRU list */
+       dlist_init(&mstate->lru_list);
+       mstate->last_tuple = NULL;
+       mstate->entry = NULL;
+
+       mstate->mem_used = 0;
+
+       /* XXX should we add something new to track these purges? */
+       mstate->stats.cache_evictions += evictions; /* Update Stats */
+}
+
 /*
  * cache_reduce_memory
  *             Evict older and less recently used items from the cache in order to
@@ -979,6 +1010,7 @@ ExecInitMemoize(Memoize *node, EState *estate, int eflags)
         * getting the first tuple.  This allows us to mark it as so.
         */
        mstate->singlerow = node->singlerow;
+       mstate->keyparamids = node->keyparamids;
 
        /*
         * Record if the cache keys should be compared bit by bit, or logically
@@ -1082,6 +1114,12 @@ ExecReScanMemoize(MemoizeState *node)
        if (outerPlan->chgParam == NULL)
                ExecReScan(outerPlan);
 
+       /*
+        * Purge the entire cache if a parameter changed that is not part of the
+        * cache key.
+        */
+       if (bms_nonempty_difference(outerPlan->chgParam, node->keyparamids))
+               cache_purge_all(node);
 }
 
 /*

diff --git a/src/backend/nodes/bitmapset.c b/src/backend/nodes/bitmapset.c
index 649478b0d4d39f5ac5c1dde6bc092c9ffa2b14c4..bff70cfb1ab179497fc4ec7202a3ce8cc9cca923 100644 (file)
--- a/src/backend/nodes/bitmapset.c
+++ b/src/backend/nodes/bitmapset.c
@@ -540,6 +540,8 @@ bms_overlap_list(const Bitmapset *a, const List *b)
 
 /*
  * bms_nonempty_difference - do sets have a nonempty difference?
+ *
+ * i.e., are any members set in 'a' that are not also set in 'b'.
  */
 bool
 bms_nonempty_difference(const Bitmapset *a, const Bitmapset *b)

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 866f19f64c1eaaacdbd154b2a3a467c6cf5fc0b0..f12660a2606fdbe97cdcf33f5479b75798489743 100644 (file)
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -280,7 +280,7 @@ 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);
+                                                        uint32 est_entries, Bitmapset *keyparamids);
 static WindowAgg *make_windowagg(List *tlist, Index winref,
                                                                 int partNumCols, AttrNumber *partColIdx, Oid *partOperators, Oid *partCollations,
                                                                 int ordNumCols, AttrNumber *ordColIdx, Oid *ordOperators, Oid *ordCollations,
@@ -1586,6 +1586,7 @@ static Memoize *
 create_memoize_plan(PlannerInfo *root, MemoizePath *best_path, int flags)
 {
        Memoize    *plan;
+       Bitmapset  *keyparamids;
        Plan       *subplan;
        Oid                *operators;
        Oid                *collations;
@@ -1617,9 +1618,11 @@ create_memoize_plan(PlannerInfo *root, MemoizePath *best_path, int flags)
                i++;
        }
 
+       keyparamids = pull_paramids((Expr *) param_exprs);
+
        plan = make_memoize(subplan, operators, collations, param_exprs,
                                                best_path->singlerow, best_path->binary_mode,
-                                               best_path->est_entries);
+                                               best_path->est_entries, keyparamids);
 
        copy_generic_path_info(&plan->plan, (Path *) best_path);
 
@@ -6420,7 +6423,7 @@ 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)
+                        uint32 est_entries, Bitmapset *keyparamids)
 {
        Memoize    *node = makeNode(Memoize);
        Plan       *plan = &node->plan;
@@ -6437,6 +6440,7 @@ make_memoize(Plan *lefttree, Oid *hashoperators, Oid *collations,
        node->singlerow = singlerow;
        node->binary_mode = binary_mode;
        node->est_entries = est_entries;
+       node->keyparamids = keyparamids;
 
        return node;
 }

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 109f93d109dd94d01d9b4bd767943b4d466834d5..873e43bfe64b663e8cd94651c1cba02a50f3ee12 100644 (file)
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -152,6 +152,7 @@ static Query *substitute_actual_srf_parameters(Query *expr,
                                                                                           int nargs, List *args);
 static Node *substitute_actual_srf_parameters_mutator(Node *node,
                                                                                                          substitute_actual_srf_parameters_context *context);
+static bool pull_paramids_walker(Node *node, Bitmapset **context);
 
 
 /*****************************************************************************
@@ -5214,3 +5215,33 @@ substitute_actual_srf_parameters_mutator(Node *node,
                                                                   substitute_actual_srf_parameters_mutator,
                                                                   (void *) context);
 }
+
+/*
+ * pull_paramids
+ *             Returns a Bitmapset containing the paramids of all Params in 'expr'.
+ */
+Bitmapset *
+pull_paramids(Expr *expr)
+{
+       Bitmapset  *result = NULL;
+
+       (void) pull_paramids_walker((Node *) expr, &result);
+
+       return result;
+}
+
+static bool
+pull_paramids_walker(Node *node, Bitmapset **context)
+{
+       if (node == NULL)
+               return false;
+       if (IsA(node, Param))
+       {
+               Param      *param = (Param *)node;
+
+               *context = bms_add_member(*context, param->paramid);
+               return false;
+       }
+       return expression_tree_walker(node, pull_paramids_walker,
+                                                                 (void *) context);
+}

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index d96ace32e43bc7ef7987a5123142c9162f685641..ddc35293326476368e0ca7799f8aca5734eb4229 100644 (file)
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -2113,6 +2113,8 @@ typedef struct MemoizeState
                                                                 * by bit, false when using hash equality ops */
        MemoizeInstrumentation stats;   /* execution statistics */
        SharedMemoizeInfo *shared_info; /* statistics for parallel workers */
+       Bitmapset          *keyparamids; /* Param->paramids of expressions belonging to
+                                                                 * param_exprs */
 } MemoizeState;
 
 /* ----------------

diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index f1328be3549b69513f9aa37e0d9dbc7cc6906483..be3c30704ad19a3f74fa73027aff8ac7504dd284 100644 (file)
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -804,6 +804,7 @@ typedef struct Memoize
        uint32          est_entries;    /* The maximum number of entries that the
                                                                 * planner expects will fit in the cache, or 0
                                                                 * if unknown */
+       Bitmapset   *keyparamids;       /* paramids from param_exprs */
 } Memoize;
 
 /* ----------------

diff --git a/src/include/optimizer/clauses.h b/src/include/optimizer/clauses.h
index 0673887a852c054f6ddac1e55d2593a6975de20a..bc3f3e60d43282c8240001824b5e2ee61a21e5d8 100644 (file)
--- a/src/include/optimizer/clauses.h
+++ b/src/include/optimizer/clauses.h
@@ -53,4 +53,6 @@ extern void CommuteOpExpr(OpExpr *clause);
 extern Query *inline_set_returning_function(PlannerInfo *root,
                                                                                        RangeTblEntry *rte);
 
+extern Bitmapset *pull_paramids(Expr *expr);
+
 #endif                                                 /* CLAUSES_H */

diff --git a/src/test/regress/expected/memoize.out b/src/test/regress/expected/memoize.out
index 0ed5d8474af090f61e1ded4205e49455702edb5a..9102957927b612c5eb160921b7d013168ee102b4 100644 (file)
--- a/src/test/regress/expected/memoize.out
+++ b/src/test/regress/expected/memoize.out
@@ -196,6 +196,45 @@ SELECT * FROM strtest s1 INNER JOIN strtest s2 ON s1.t >= s2.t;', false);
 (8 rows)
 
 DROP TABLE strtest;
+-- Exercise Memoize code that flushes the cache when a parameter changes which
+-- is not part of the cache key.
+-- Ensure we get a Memoize plan
+EXPLAIN (COSTS OFF)
+SELECT UNIQUE1 FROM tenk1 t0
+WHERE unique1 < 3
+  AND EXISTS (
+       SELECT 1 FROM tenk1 t1
+       INNER JOIN tenk2 t2 ON t1.unique1 = t2.hundred
+       WHERE t0.ten = t1.twenty AND t0.two <> t2.four OFFSET 0);
+                           QUERY PLAN                           
+----------------------------------------------------------------
+ Index Scan using tenk1_unique1 on tenk1 t0
+   Index Cond: (unique1 < 3)
+   Filter: (SubPlan 1)
+   SubPlan 1
+     ->  Nested Loop
+           ->  Index Scan using tenk2_hundred on tenk2 t2
+                 Filter: (t0.two <> four)
+           ->  Memoize
+                 Cache Key: t2.hundred
+                 Cache Mode: logical
+                 ->  Index Scan using tenk1_unique1 on tenk1 t1
+                       Index Cond: (unique1 = t2.hundred)
+                       Filter: (t0.ten = twenty)
+(13 rows)
+
+-- Ensure the above query returns the correct result
+SELECT UNIQUE1 FROM tenk1 t0
+WHERE unique1 < 3
+  AND EXISTS (
+       SELECT 1 FROM tenk1 t1
+       INNER JOIN tenk2 t2 ON t1.unique1 = t2.hundred
+       WHERE t0.ten = t1.twenty AND t0.two <> t2.four OFFSET 0);
+ unique1 
+---------
+       2
+(1 row)
+
 RESET enable_seqscan;
 RESET enable_mergejoin;
 RESET work_mem;

diff --git a/src/test/regress/sql/memoize.sql b/src/test/regress/sql/memoize.sql
index 3c7360adf9c8f74d2fb6ee9462b7d32ee06d3985..00f38f933cc77da90c2a50247af88c9b909bffa2 100644 (file)
--- a/src/test/regress/sql/memoize.sql
+++ b/src/test/regress/sql/memoize.sql
@@ -103,6 +103,26 @@ SELECT * FROM strtest s1 INNER JOIN strtest s2 ON s1.t >= s2.t;', false);
 
 DROP TABLE strtest;
 
+-- Exercise Memoize code that flushes the cache when a parameter changes which
+-- is not part of the cache key.
+
+-- Ensure we get a Memoize plan
+EXPLAIN (COSTS OFF)
+SELECT UNIQUE1 FROM tenk1 t0
+WHERE unique1 < 3
+  AND EXISTS (
+       SELECT 1 FROM tenk1 t1
+       INNER JOIN tenk2 t2 ON t1.unique1 = t2.hundred
+       WHERE t0.ten = t1.twenty AND t0.two <> t2.four OFFSET 0);
+
+-- Ensure the above query returns the correct result
+SELECT UNIQUE1 FROM tenk1 t0
+WHERE unique1 < 3
+  AND EXISTS (
+       SELECT 1 FROM tenk1 t1
+       INNER JOIN tenk2 t2 ON t1.unique1 = t2.hundred
+       WHERE t0.ten = t1.twenty AND t0.two <> t2.four OFFSET 0);
+
 RESET enable_seqscan;
 RESET enable_mergejoin;
 RESET work_mem;