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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
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9 files changed

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-3
lines changed

9 files changed

+142
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‎src/backend/executor/nodeMemoize.c

Lines changed: 38 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -367,6 +367,37 @@ remove_cache_entry(MemoizeState *mstate, MemoizeEntry *entry)
367367
pfree(key);
368368
}
369369

370+
/*
371+
* cache_purge_all
372+
* Remove all items from the cache
373+
*/
374+
static void
375+
cache_purge_all(MemoizeState *mstate)
376+
{
377+
uint64 evictions = mstate->hashtable->members;
378+
PlanState *pstate = (PlanState *) mstate;
379+
380+
/*
381+
* Likely the most efficient way to remove all items is to just reset the
382+
* memory context for the cache and then rebuild a fresh hash table. This
383+
* saves having to remove each item one by one and pfree each cached tuple
384+
*/
385+
MemoryContextReset(mstate->tableContext);
386+
387+
/* Make the hash table the same size as the original size */
388+
build_hash_table(mstate, ((Memoize *) pstate->plan)->est_entries);
389+
390+
/* reset the LRU list */
391+
dlist_init(&mstate->lru_list);
392+
mstate->last_tuple = NULL;
393+
mstate->entry = NULL;
394+
395+
mstate->mem_used = 0;
396+
397+
/* XXX should we add something new to track these purges? */
398+
mstate->stats.cache_evictions += evictions; /* Update Stats */
399+
}
400+
370401
/*
371402
* cache_reduce_memory
372403
* Evict older and less recently used items from the cache in order to
@@ -979,6 +1010,7 @@ ExecInitMemoize(Memoize *node, EState *estate, int eflags)
9791010
* getting the first tuple. This allows us to mark it as so.
9801011
*/
9811012
mstate->singlerow = node->singlerow;
1013+
mstate->keyparamids = node->keyparamids;
9821014

9831015
/*
9841016
* Record if the cache keys should be compared bit by bit, or logically
@@ -1082,6 +1114,12 @@ ExecReScanMemoize(MemoizeState *node)
10821114
if (outerPlan->chgParam == NULL)
10831115
ExecReScan(outerPlan);
10841116

1117+
/*
1118+
* Purge the entire cache if a parameter changed that is not part of the
1119+
* cache key.
1120+
*/
1121+
if (bms_nonempty_difference(outerPlan->chgParam, node->keyparamids))
1122+
cache_purge_all(node);
10851123
}
10861124

10871125
/*

‎src/backend/nodes/bitmapset.c

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -540,6 +540,8 @@ bms_overlap_list(const Bitmapset *a, const List *b)
540540

541541
/*
542542
* bms_nonempty_difference - do sets have a nonempty difference?
543+
*
544+
* i.e., are any members set in 'a' that are not also set in 'b'.
543545
*/
544546
bool
545547
bms_nonempty_difference(const Bitmapset *a, const Bitmapset *b)

‎src/backend/optimizer/plan/createplan.c

Lines changed: 7 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -280,7 +280,7 @@ static Material *make_material(Plan *lefttree);
280280
static Memoize *make_memoize(Plan *lefttree, Oid *hashoperators,
281281
Oid *collations, List *param_exprs,
282282
bool singlerow, bool binary_mode,
283-
uint32 est_entries);
283+
uint32 est_entries, Bitmapset *keyparamids);
284284
static WindowAgg *make_windowagg(List *tlist, Index winref,
285285
int partNumCols, AttrNumber *partColIdx, Oid *partOperators, Oid *partCollations,
286286
int ordNumCols, AttrNumber *ordColIdx, Oid *ordOperators, Oid *ordCollations,
@@ -1586,6 +1586,7 @@ static Memoize *
15861586
create_memoize_plan(PlannerInfo *root, MemoizePath *best_path, int flags)
15871587
{
15881588
Memoize *plan;
1589+
Bitmapset *keyparamids;
15891590
Plan *subplan;
15901591
Oid *operators;
15911592
Oid *collations;
@@ -1617,9 +1618,11 @@ create_memoize_plan(PlannerInfo *root, MemoizePath *best_path, int flags)
16171618
i++;
16181619
}
16191620

1621+
keyparamids = pull_paramids((Expr *) param_exprs);
1622+
16201623
plan = make_memoize(subplan, operators, collations, param_exprs,
16211624
best_path->singlerow, best_path->binary_mode,
1622-
best_path->est_entries);
1625+
best_path->est_entries, keyparamids);
16231626

16241627
copy_generic_path_info(&plan->plan, (Path *) best_path);
16251628

@@ -6420,7 +6423,7 @@ materialize_finished_plan(Plan *subplan)
64206423
static Memoize *
64216424
make_memoize(Plan *lefttree, Oid *hashoperators, Oid *collations,
64226425
List *param_exprs, bool singlerow, bool binary_mode,
6423-
uint32 est_entries)
6426+
uint32 est_entries, Bitmapset *keyparamids)
64246427
{
64256428
Memoize *node = makeNode(Memoize);
64266429
Plan *plan = &node->plan;
@@ -6437,6 +6440,7 @@ make_memoize(Plan *lefttree, Oid *hashoperators, Oid *collations,
64376440
node->singlerow = singlerow;
64386441
node->binary_mode = binary_mode;
64396442
node->est_entries = est_entries;
6443+
node->keyparamids = keyparamids;
64406444

64416445
return node;
64426446
}

‎src/backend/optimizer/util/clauses.c

Lines changed: 31 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -152,6 +152,7 @@ static Query *substitute_actual_srf_parameters(Query *expr,
152152
int nargs, List *args);
153153
static Node *substitute_actual_srf_parameters_mutator(Node *node,
154154
substitute_actual_srf_parameters_context *context);
155+
static bool pull_paramids_walker(Node *node, Bitmapset **context);
155156

156157

157158
/*****************************************************************************
@@ -5214,3 +5215,33 @@ substitute_actual_srf_parameters_mutator(Node *node,
52145215
substitute_actual_srf_parameters_mutator,
52155216
(void *) context);
52165217
}
5218+
5219+
/*
5220+
* pull_paramids
5221+
* Returns a Bitmapset containing the paramids of all Params in 'expr'.
5222+
*/
5223+
Bitmapset *
5224+
pull_paramids(Expr *expr)
5225+
{
5226+
Bitmapset *result = NULL;
5227+
5228+
(void) pull_paramids_walker((Node *) expr, &result);
5229+
5230+
return result;
5231+
}
5232+
5233+
static bool
5234+
pull_paramids_walker(Node *node, Bitmapset **context)
5235+
{
5236+
if (node == NULL)
5237+
return false;
5238+
if (IsA(node, Param))
5239+
{
5240+
Param *param = (Param *)node;
5241+
5242+
*context = bms_add_member(*context, param->paramid);
5243+
return false;
5244+
}
5245+
return expression_tree_walker(node, pull_paramids_walker,
5246+
(void *) context);
5247+
}

‎src/include/nodes/execnodes.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2113,6 +2113,8 @@ typedef struct MemoizeState
21132113
* by bit, false when using hash equality ops */
21142114
MemoizeInstrumentation stats; /* execution statistics */
21152115
SharedMemoizeInfo *shared_info; /* statistics for parallel workers */
2116+
Bitmapset *keyparamids; /* Param->paramids of expressions belonging to
2117+
* param_exprs */
21162118
} MemoizeState;
21172119

21182120
/* ----------------

‎src/include/nodes/plannodes.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -804,6 +804,7 @@ typedef struct Memoize
804804
uint32 est_entries; /* The maximum number of entries that the
805805
* planner expects will fit in the cache, or 0
806806
* if unknown */
807+
Bitmapset *keyparamids; /* paramids from param_exprs */
807808
} Memoize;
808809

809810
/* ----------------

‎src/include/optimizer/clauses.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -53,4 +53,6 @@ extern void CommuteOpExpr(OpExpr *clause);
5353
extern Query *inline_set_returning_function(PlannerInfo *root,
5454
RangeTblEntry *rte);
5555

56+
extern Bitmapset *pull_paramids(Expr *expr);
57+
5658
#endif /* CLAUSES_H */

‎src/test/regress/expected/memoize.out

Lines changed: 39 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -196,6 +196,45 @@ SELECT * FROM strtest s1 INNER JOIN strtest s2 ON s1.t >= s2.t;', false);
196196
(8 rows)
197197

198198
DROP TABLE strtest;
199+
-- Exercise Memoize code that flushes the cache when a parameter changes which
200+
-- is not part of the cache key.
201+
-- Ensure we get a Memoize plan
202+
EXPLAIN (COSTS OFF)
203+
SELECT UNIQUE1 FROM tenk1 t0
204+
WHERE unique1 < 3
205+
AND EXISTS (
206+
SELECT 1 FROM tenk1 t1
207+
INNER JOIN tenk2 t2 ON t1.unique1 = t2.hundred
208+
WHERE t0.ten = t1.twenty AND t0.two <> t2.four OFFSET 0);
209+
QUERY PLAN
210+
----------------------------------------------------------------
211+
Index Scan using tenk1_unique1 on tenk1 t0
212+
Index Cond: (unique1 < 3)
213+
Filter: (SubPlan 1)
214+
SubPlan 1
215+
-> Nested Loop
216+
-> Index Scan using tenk2_hundred on tenk2 t2
217+
Filter: (t0.two <> four)
218+
-> Memoize
219+
Cache Key: t2.hundred
220+
Cache Mode: logical
221+
-> Index Scan using tenk1_unique1 on tenk1 t1
222+
Index Cond: (unique1 = t2.hundred)
223+
Filter: (t0.ten = twenty)
224+
(13 rows)
225+
226+
-- Ensure the above query returns the correct result
227+
SELECT UNIQUE1 FROM tenk1 t0
228+
WHERE unique1 < 3
229+
AND EXISTS (
230+
SELECT 1 FROM tenk1 t1
231+
INNER JOIN tenk2 t2 ON t1.unique1 = t2.hundred
232+
WHERE t0.ten = t1.twenty AND t0.two <> t2.four OFFSET 0);
233+
unique1
234+
---------
235+
2
236+
(1 row)
237+
199238
RESET enable_seqscan;
200239
RESET enable_mergejoin;
201240
RESET work_mem;

‎src/test/regress/sql/memoize.sql

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -103,6 +103,26 @@ SELECT * FROM strtest s1 INNER JOIN strtest s2 ON s1.t >= s2.t;', false);
103103

104104
DROP TABLE strtest;
105105

106+
-- Exercise Memoize code that flushes the cache when a parameter changes which
107+
-- is not part of the cache key.
108+
109+
-- Ensure we get a Memoize plan
110+
EXPLAIN (COSTS OFF)
111+
SELECT UNIQUE1 FROM tenk1 t0
112+
WHERE unique1 < 3
113+
AND EXISTS (
114+
SELECT 1 FROM tenk1 t1
115+
INNER JOIN tenk2 t2 ON t1.unique1 = t2.hundred
116+
WHERE t0.ten = t1.twenty AND t0.two <> t2.four OFFSET 0);
117+
118+
-- Ensure the above query returns the correct result
119+
SELECT UNIQUE1 FROM tenk1 t0
120+
WHERE unique1 < 3
121+
AND EXISTS (
122+
SELECT 1 FROM tenk1 t1
123+
INNER JOIN tenk2 t2 ON t1.unique1 = t2.hundred
124+
WHERE t0.ten = t1.twenty AND t0.two <> t2.four OFFSET 0);
125+
106126
RESET enable_seqscan;
107127
RESET enable_mergejoin;
108128
RESET work_mem;

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