Re: Postgres-R: internal messaging

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Markus Wanner <markus(at)bluegap(dot)ch>
Cc: Alexey Klyukin <alexk(at)commandprompt(dot)com>, PostgreSQL-development Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Postgres-R: internal messaging
Date: 2008-07-23 20:51:42
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Markus Wanner <markus(at)bluegap(dot)ch> writes:
> ... crashes are more difficult. IMO the replication
> manager needs to stay alive during this reinitialization, to keep the
> GCS connection. However, it can easily detach from shared memory
> temporarily (the imessages stuff is the only shmem place it touches,
> IIRC). However, a more difficult aspect is: it must be able to tell if a
> backend has applied its transaction *before* it died or not. Thus, after
> all backends have been killed, the postmaster needs to wait with
> reinitializing shared memory, until the replication manager has consumed
> all its messages. (Otherwise we would risk "losing" local transactions,
> probably also remote ones).

I hope you're not expecting the contents of shared memory to still be
trustworthy after a backend crash. If the manager is working strictly
from its own local memory, then it would be reasonable to operate
as above.

regards, tom lane

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