| From: | Amul Sul <sulamul(at)gmail(dot)com> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
| Cc: | "Bossart, Nathan" <bossartn(at)amazon(dot)com>, "Jakub(dot)Wartak(at)tomtom(dot)com" <Jakub(dot)Wartak(at)tomtom(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, Ryo Matsumura <matsumura(dot)ryo(at)fujitsu(dot)com>, "andres(at)anarazel(dot)de" <andres(at)anarazel(dot)de>, "masao(dot)fujii(at)oss(dot)nttdata(dot)com" <masao(dot)fujii(at)oss(dot)nttdata(dot)com>, "mengjuan(dot)cmj(at)alibaba-inc(dot)com" <mengjuan(dot)cmj(at)alibaba-inc(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: prevent immature WAL streaming |
| Date: | 2021-10-07 13:22:39 |
| Message-ID: | CAAJ_b97FcTG7Gu5f3Kd-zKGEkG=hXnVPQAOo9G8EvpTehS-uCg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, 7 Oct 2021 at 6:41 PM, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
wrote:
> On 2021-Oct-07, Amul Sul wrote:
>
> > While reading this commit (ff9f111bce24), wondered can't we skip
> > missingContrecPtr global variable declaration and calculate that from
> > abortedRecPtr value whenever it needed. IIUC, missingContrecPtr is the
> > next page to the page that abortedRecPtr contain and that can be
> > calculated as "abortedRecPtr + (XLOG_BLCKSZ - (abortedRecPtr %
> > XLOG_BLCKSZ))", thoughts? Please correct me if I'm missing something,
> > thanks.
>
> I don't think that works -- what if the missing record is not on the
> next page but on some future one? Imagine an enormously large record
> that starts on segment 1, covers all of segment 2 and ends in segment 3.
> We could have flushed segment 2 already, so with your idea we would skip
> ahead only to that position, but really we need to skip all the way to
> the first page of segment 3.
>
> This is easier to imagine if you set wal segment size to 1 MB, but it is
> possible with the default segment size too, since commit records can be
> arbitrarily large, and "logical message" records as well.
Make sense, thanks for the explanation.
Regards,
Amul
--
Regards,
Amul Sul
EDB: http://www.enterprisedb.com
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