Re: [EXTERNAL] Re: Crash in record_type_typmod_compare

Hi Andres,

Please see the updated patch, do you mean something like this? (there might be a simpler way for doing this)

Best,
Talha.
________________________________
From: Andres Freund <andres(at)anarazel(dot)de>
Sent: Wednesday, March 31, 2021 10:49 PM
To: Sait Talha Nisanci <Sait(dot)Nisanci(at)microsoft(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>; Metin Doslu <Metin(dot)Doslu(at)microsoft(dot)com>
Subject: [EXTERNAL] Re: Crash in record_type_typmod_compare

Hi,

On 2021-03-31 13:26:34 +0000, Sait Talha Nisanci wrote:
> diff --git a/src/backend/utils/cache/typcache.c b/src/backend/utils/cache/typcache.c
> index 4915ef5934..4757e8fa80 100644
> --- a/src/backend/utils/cache/typcache.c
> +++ b/src/backend/utils/cache/typcache.c
> @@ -1970,18 +1970,16 @@ assign_record_type_typmod(TupleDesc tupDesc)
> CreateCacheMemoryContext();
> }
>
> - /* Find or create a hashtable entry for this tuple descriptor */
> + /* Find a hashtable entry for this tuple descriptor */
> recentry = (RecordCacheEntry *) hash_search(RecordCacheHash,
> (void *) &tupDesc,
> - HASH_ENTER, &found);
> + HASH_FIND, &found);
> if (found && recentry->tupdesc != NULL)
> {
> tupDesc->tdtypmod = recentry->tupdesc->tdtypmod;
> return;
> }
>
> - /* Not present, so need to manufacture an entry */
> - recentry->tupdesc = NULL;
> oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
>
> /* Look in the SharedRecordTypmodRegistry, if attached */
> @@ -1995,6 +1993,10 @@ assign_record_type_typmod(TupleDesc tupDesc)
> }
> ensure_record_cache_typmod_slot_exists(entDesc->tdtypmod);
> RecordCacheArray[entDesc->tdtypmod] = entDesc;
> + /* Not present, so need to manufacture an entry */
> + recentry = (RecordCacheEntry *) hash_search(RecordCacheHash,
> + (void *) &tupDesc,
> + HASH_ENTER, NULL);
> recentry->tupdesc = entDesc;

ISTM that the ensure_record_cache_typmod_slot_exists() should be moved
to before find_or_make_matching_shared_tupledesc /
CreateTupleDescCopy. Otherwise we can leak if the CreateTupleDescCopy()
succeeds but ensure_record_cache_typmod_slot_exists() fails. Conversely,
if ensure_record_cache_typmod_slot_exists() succeeds, but
CreateTupleDescCopy() we won't leak, since the former is just
repalloc()ing allocations.

Greetings,

Andres Freund