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Flush Memoize cache when non-key parameters change

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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
This commit is contained in:
David Rowley
2021-11-24 14:56:18 +13:00
parent e502150f7d
commit 1050048a31
9 changed files with 142 additions and 3 deletions
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38
src/backend/executor/nodeMemoize.c
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@ -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);
}
/*