From: alvherre@alvh.no-ip.org <alvherre@alvh.no-ip.org>
To: Bossart, Nathan <bossartn@amazon.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org <pgsql-hackers@lists.postgresql.org>
Cc: mengjuan.cmj@alibaba-inc.com <mengjuan.cmj@alibaba-inc.com>
Cc: Jakub.Wartak@tomtom.com <Jakub.Wartak@tomtom.com>
Subject: Re: prevent immature WAL streaming
Date: Wed, 25 Aug 2021 08:32:31 -0400
Message-ID: <202108251232.aaxpgvj3rcvw@alvherre.pgsql> (raw)
In-Reply-To: <8687C486-BC80-4150-8519-13FE395485BF@amazon.com>
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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To: pgsql-hackers@postgresql.org
Cc: alvherre@alvh.no-ip.org, bossartn@amazon.com, horikyota.ntt@gmail.com, pgsql-hackers@lists.postgresql.org, mengjuan.cmj@alibaba-inc.com, Jakub.Wartak@tomtom.com
Subject: Re: prevent immature WAL streaming
In-Reply-To: <202108251232.aaxpgvj3rcvw@alvherre.pgsql>
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