Re: PATCH: logical_work_mem and logical streaming of large in-progress transactions

On Thu, Jul 9, 2020 at 8:18 AM Ajin Cherian <itsajin(at)gmail(dot)com> wrote:
>
> On Thu, Jul 9, 2020 at 12:28 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>
>> On Wed, Jul 8, 2020 at 7:31 PM Ajin Cherian <itsajin(at)gmail(dot)com> wrote:
>>
>> Thanks for showing the interest in patch. How have you ensured that
>> streaming is happening? I don't think the proposed patch can ensure
>> it for every case because we also rely on logical_decoding_work_mem to
>> decide whether to stream/spill, see ReorderBufferCheckMemoryLimit. I
>> think with your patch it will allow streaming for cases where we have
>> large amount of WAL to decode.
>>
>
> Maybe I missed something but I looked at ReorderBufferCheckMemoryLimit, even there it checks the same function ReorderBufferCanStream () and decides whether to stream or spill. Did I miss something?
>
> while (rb->size >= logical_decoding_work_mem * 1024L)
> {

There is a check before above loop:

ReorderBufferCheckMemoryLimit(ReorderBuffer *rb)
{
ReorderBufferTXN *txn;

/* bail out if we haven't exceeded the memory limit */
if (rb->size < logical_decoding_work_mem * 1024L)
return;

This will prevent the streaming/spill to occur.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com