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Commitfa5185b

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Harden Memoization code against broken data types
Bug #17512 highlighted that a suitably broken data type could cause thebackend to crash if either the hash function or equality function were insomeway non-deterministic based on their input values. Such a data typecould cause a crash of the backend due to some code which assumes thatwe'll always find a hash table entry corresponding to an item in theMemoize LRU list.Here we remove the assumption that we'll always find the entrycorresponding to the given LRU list item and add run-time checks to verifywe have found the given item in the cache.This is not a fix for bug #17512, but it will turn the crash reported bythat bug report into an internal ERROR.Reported-by: Ales ZelenyReviewed-by: Tom LaneDiscussion:https://postgr.es/m/CAApHDvpxFSTwvoYWT7kmFVSZ9zLAeHb=S9vrz=RExMgSkQNWqw@mail.gmail.comBackpatch-through: 14, where Memoize was added.
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‎src/backend/executor/nodeMemoize.c

Lines changed: 7 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -446,9 +446,13 @@ cache_reduce_memory(MemoizeState *mstate, MemoizeKey *specialkey)
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*/
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entry=memoize_lookup(mstate->hashtable,NULL);
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/* A good spot to check for corruption of the table and LRU list. */
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Assert(entry!=NULL);
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Assert(entry->key==key);
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/*
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* Sanity check that we found the entry belonging to the LRU list
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* item. A misbehaving hash or equality function could cause the
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* entry not to be found or the wrong entry to be found.
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*/
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if (unlikely(entry==NULL||entry->key!=key))
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elog(ERROR,"could not find memoization table entry");
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/*
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* If we're being called to free memory while the cache is being

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