From c1500a1ba7e16ac9e98c6baf792f0be64a48e839 Mon Sep 17 00:00:00 2001 From: Alexander Korotkov <akorotkov@postgresql.org> Date: Thu, 24 Oct 2024 14:34:16 +0300 Subject: [PATCH] Update header comment for lookup_type_cache() Describe the way we handle concurrent invalidation messages. Discussion: https://postgr.es/m/CAPpHfdsQhwUrnB3of862j9RgHoJM--eRbifvBMvtQxpC57dxCA%40mail.gmail.com Reviewed-by: Andrei Lepikhov, Artur Zakirov, Pavel Borisov --- src/backend/utils/cache/typcache.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/src/backend/utils/cache/typcache.c b/src/backend/utils/cache/typcache.c index 2ec136b7d30..f142624ad2e 100644 --- a/src/backend/utils/cache/typcache.c +++ b/src/backend/utils/cache/typcache.c @@ -351,6 +351,15 @@ type_cache_syshash(const void *key, Size keysize) * invalid. Note however that we may fail to find one or more of the * values requested by 'flags'; the caller needs to check whether the fields * are InvalidOid or not. + * + * Note that while filling TypeCacheEntry we might process concurrent + * invalidation messages, causing our not-yet-filled TypeCacheEntry to be + * invalidated. In this case, we typically only clear flags while values are + * still available for the caller. It's expected that the caller holds + * enough locks on type-depending objects that the values are still relevant. + * It's also important that the tupdesc is filled after all other + * TypeCacheEntry items for TYPTYPE_COMPOSITE. So, tupdesc can't get + * invalidated during the lookup_type_cache() call. */ TypeCacheEntry * lookup_type_cache(Oid type_id, int flags)