Re: Fix comment for max_cached_tuplebufs definition

On Fri, Feb 7, 2020 at 02:49:14PM +0530, Kuntal Ghosh wrote:
> Hello Hackers,
>
> While working on some issue in logical decoding, I found some
> inconsistencies in the comment for defining max_cached_tuplebufs in
> reorderbuffer.c. It only exists till PG10 because after that the
> definition got removed by the generational memory allocator patch. The
> variable is defined as follows in reorderbuffer.c:
> static const Size max_cached_tuplebufs = 4096 * 2; /* ~8MB */
>
> And it gets compared with rb->nr_cached_tuplebufs in
> ReorderBufferReturnTupleBuf as follows:
> if (tuple->alloc_tuple_size == MaxHeapTupleSize &&
> rb->nr_cached_tuplebufs < max_cached_tuplebufs)
>
> {
> rb->nr_cached_tuplebufs++;
> }
>
> So, what this variable actually tracks is 4096 * 2 times
> MaxHeapTupleSize amount of memory which is approximately 64MB. I've
> attached a patch to modify the comment.
>
> But, I'm not sure whether the intention was to keep 8MB cache only. In
> that case, I can come up with another patch.

Yes, I see you are correct, since each tuplebuf is MaxHeapTupleSize.
Patch applied from PG 9.5 to PG 10. Thanks.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EnterpriseDB https://enterprisedb.com

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