From: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
---|---|
To: | Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> |
Cc: | Andres Freund <andres(at)anarazel(dot)de>, nag1010(at)gmail(dot)com, jdnelson(at)dyn(dot)com, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [BUGS] Bug in Physical Replication Slots (at least 9.5)? |
Date: | 2017-10-26 18:13:55 |
Message-ID: | CAB7nPqSaWrJD0fVN4uX=e=D9FqEYqPq-S2X_TC60kJ0YX2-5eQ@mail.gmail.com |
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On Thu, Oct 26, 2017 at 3:05 AM, Kyotaro HORIGUCHI
<horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> The largest obstacle to do that is that walreceiver is not
> utterly concerned to record internals. In other words, it doesn't
> know what a record is. Teaching that introduces much complexity
> and the complexity slows down the walreceiver.
>
> Addition to that, this "problem" occurs also on replication
> without a slot. The latest patch also help the case.
That's why replication slots have been introduced to begin with. The
WAL receiver gives no guarantee that a segment will be retained or not
based on the beginning of a record. That's sad that the WAL receiver
does not track properly restart LSN and instead just uses the flush
LSN. I am beginning to think that a new message type used to report
the restart LSN when a replication slot is in use would just be a
better and more stable solution. I haven't looked at the
implementation details yet though.
--
Michael
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