Re: Some memory not freed at the exit of RelationBuildPartitionDesc()

Hi Amul,

On Thu, Aug 8, 2019 at 4:15 PM amul sul <sulamul(at)gmail(dot)com> wrote:
>
> Hi,
>
> In RelationBuildPartitionDesc(), a memory space that use to gather partitioning
> bound info wasn't free at the end. This might not a problem because this
> allocated memory will eventually be recovered when the top-level context is
> freed, but the case when a partitioned table having 1000s or more partitions and
> this partitioned relation open & close, and its cached entry invalidated in loop
> then we'll have too may call to RelationBuildPartitionDesc() which will keep
> wasting some space with every loop.
>
> For a demonstration purpose, I did the following changes to
> heap_drop_with_catalog() and tried to drop a partitioned table having 5000
> partitions(attached create script) which hit OOM on a machine in no time:
>
> diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
> index b7bcdd9d0f..6b7bc0d7ae 100644
> --- a/src/backend/catalog/heap.c
> +++ b/src/backend/catalog/heap.c
> @@ -1842,6 +1842,8 @@ heap_drop_with_catalog(Oid relid)
> parentOid = get_partition_parent(relid);
> LockRelationOid(parentOid, AccessExclusiveLock);
>
> + rel = relation_open(parentOid, NoLock);
> + relation_close(rel, NoLock);
> /*
> * If this is not the default partition, dropping it will change the
> * default partition's partition constraint, so we must lock it.
>
>
> I think we should do all partitioned bound information gathering and
> calculation in temporary memory context which can be released at the end of
> RelationBuildPartitionDesc(), thoughts/Comments?
>
> I did the same in the attached patch and the aforesaid OOM issue is disappeared.

Thanks for the patch. This was discussed recently in the "hyrax vs.
RelationBuildPartitionDesc()" thread [1] and I think Alvaro proposed
an approach that's similar to yours. Not sure why it wasn't pursued
though. Maybe the reason is buried somewhere in that discussion.

Thanks,
Amit

[1] https://www.postgresql.org/message-id/flat/CA%2BTgmoY3bRmGB6-DUnoVy5fJoreiBJ43rwMrQRCdPXuKt4Ykaw%40mail.gmail.com