| From: | "alvherre(at)alvh(dot)no-ip(dot)org" <alvherre(at)alvh(dot)no-ip(dot)org> |
|---|---|
| To: | "Bossart, Nathan" <bossartn(at)amazon(dot)com> |
| Cc: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>, "mengjuan(dot)cmj(at)alibaba-inc(dot)com" <mengjuan(dot)cmj(at)alibaba-inc(dot)com>, "Jakub(dot)Wartak(at)tomtom(dot)com" <Jakub(dot)Wartak(at)tomtom(dot)com> |
| Subject: | Re: prevent immature WAL streaming |
| Date: | 2021-08-25 12:32:31 |
| Message-ID: | 202108251232.aaxpgvj3rcvw@alvherre.pgsql |
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| Lists: | pgsql-hackers |
On 2021-Aug-24, Bossart, Nathan wrote:
> If moving RegisterSegmentBoundary() is sufficient to prevent the flush
> pointer from advancing before we register the boundary, I bet we could
> also remove the WAL writer nudge.
Can you elaborate on this? I'm not sure I see the connection.
> Another interesting thing I see is that the boundary stored in
> earliestSegBoundary is not necessarily the earliest one. It's just
> the first one that has been registered. I did this for simplicity for
> the .ready file fix, but I can see it causing problems here.
Hmm, is there really a problem here? Surely the flush point cannot go
past whatever has been written. If somebody is writing an earlier
section of WAL, then we cannot move the flush pointer to a later
position. So it doesn't matter if the earliest point we have registered
is the true earliest -- we only care for it to be the earliest that is
past the flush point.
--
Álvaro Herrera Valdivia, Chile — https://www.EnterpriseDB.com/
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