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

On Thu, Jul 9, 2020 at 8:47 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Thu, Jul 9, 2020 at 8:18 AM Ajin Cherian <itsajin@gmail.com> wrote:
> >
> > On Thu, Jul 9, 2020 at 12:28 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >>
> >> On Wed, Jul 8, 2020 at 7:31 PM Ajin Cherian <itsajin@gmail.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.

I think if the GUC is set then maybe we can bypass this check so that
it can try to stream every single change?

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com