Re: Improve eviction algorithm in ReorderBuffer

On Tue, Dec 19, 2023 at 8:02 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Tue, Dec 19, 2023 at 8:31 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > On Sun, Dec 17, 2023 at 11:40 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > >
> > > The individual transactions shouldn't cross
> > > 'logical_decoding_work_mem'. I got a bit confused by your proposal to
> > > maintain the lists: "...splitting it into two lists: transactions
> > > consuming 5% < and 5% >= of the memory limit, and checking the 5% >=
> > > list preferably.". In the previous sentence, what did you mean by
> > > transactions consuming 5% >= of the memory limit? I got the impression
> > > that you are saying to maintain them in a separate transaction list
> > > which doesn't seems to be the case.
> >
> > I wanted to mean that there are three lists in total: the first one
> > maintain the transactions consuming more than 10% of
> > logical_decoding_work_mem,
> >
>
> How can we have multiple transactions in the list consuming more than
> 10% of logical_decoding_work_mem? Shouldn't we perform serialization
> before any xact reaches logical_decoding_work_mem?

Well, suppose logical_decoding_work_mem is set to 64MB, transactions
consuming more than 6.4MB are added to the list. So for example, it's
possible that the list has three transactions each of which are
consuming 10MB while the total memory usage in the reorderbuffer is
still 30MB (less than logical_decoding_work_mem).

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com