| From: | SATYANARAYANA NARLAPURAM <satyanarlapuram(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Jeff Davis <pgsql(at)j-davis(dot)com>, Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: Improve WALRead() to suck data directly from WAL buffers when possible |
| Date: | 2023-01-25 20:27:30 |
| Message-ID: | CAHg+QDcrb7VpwDq7LctajUf0-9Z2T2R3nSd7AqeJxk8b8o9s-w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sat, Jan 14, 2023 at 12:34 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> Hi,
>
> On 2023-01-14 00:48:52 -0800, Jeff Davis wrote:
> > On Mon, 2022-12-26 at 14:20 +0530, Bharath Rupireddy wrote:
> > > Please review the attached v2 patch further.
> >
> > I'm still unclear on the performance goals of this patch. I see that it
> > will reduce syscalls, which sounds good, but to what end?
> >
> > Does it allow a greater number of walsenders? Lower replication
> > latency? Less IO bandwidth? All of the above?
>
> One benefit would be that it'd make it more realistic to use direct IO for
> WAL
> - for which I have seen significant performance benefits. But when we
> afterwards have to re-read it from disk to replicate, it's less clearly a
> win.
>
+1. Archive modules rely on reading the wal files for PITR. Direct IO for
WAL requires reading these files from disk anyways for archival. However,
Archiving using utilities like pg_receivewal can take advantage of this
patch together with direct IO for WAL.
Thanks,
Satya
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