Re: Improve eviction algorithm in ReorderBuffer

On Fri, Mar 29, 2024 at 7:37 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Fri, Mar 29, 2024 at 12:13 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > On Fri, Mar 29, 2024 at 2:09 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> > >
> > > On Tue, 26 Mar 2024 at 10:05, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > > >
> > > > On Thu, Mar 14, 2024 at 12:02 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > > > >
> > > > >
> > > > > I've attached new version patches.
> > > >
> > > > Since the previous patch conflicts with the current HEAD, I've
> > > > attached the rebased patches.
> > >
> > > Thanks for the updated patch.
> > > One comment:
> > > I felt we can mention the improvement where we update memory
> > > accounting info at transaction level instead of per change level which
> > > is done in ReorderBufferCleanupTXN, ReorderBufferTruncateTXN, and
> > > ReorderBufferSerializeTXN also in the commit message:
> >
> > Agreed.
> >
> > I think the patch is in good shape. I'll push the patch with the
> > suggestion next week, barring any objections.
> >
>
> Few minor comments:
> 1.
> @@ -3636,6 +3801,8 @@ ReorderBufferCheckMemoryLimit(ReorderBuffer *rb)
> Assert(txn->nentries_mem == 0);
> }
>
> + ReorderBufferMaybeResetMaxHeap(rb);
> +
>
> Can we write a comment about why this reset is required here?
> Otherwise, the reason is not apparent.

Yes, added.

>
> 2.
> Although using max-heap to select the largest
> + * transaction is effective when there are many transactions being decoded,
> + * there is generally no need to use it as long as all transactions being
> + * decoded are top-level transactions. Therefore, we use MaxConnections as the
> + * threshold so we can prevent switching to the state unless we use
> + * subtransactions.
> + */
> +#define MAX_HEAP_TXN_COUNT_THRESHOLD MaxConnections
>
> Isn't using max-heap equally effective in finding the largest
> transaction whether there are top-level or top-level plus
> subtransactions? This comment indicates it is only effective when
> there are subtransactions.

You're right. Updated the comment.

I've attached the updated patches.

Regards,

--
Masahiko Sawada
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