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Re: Error code for "terminating connection due to conflict with recovery"

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Bruce Momjian <bruce(at)momjian(dot)us>, fgp(at)phlo(dot)org, Tatsuo Ishii <ishii(at)postgresql(dot)org>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Error code for "terminating connection due to conflict with recovery"
Date: 2011-02-01 01:52:04
Message-ID: 13000.1296525124@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Jan 31, 2011 at 7:25 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>>> Seems a little weird to me, since the administrator hasn't done
>>> anything.

>> Sure he has: he issued the DROP DATABASE command that's causing the
>> system to disconnect standby sessions.

> Well, I'm not sure how much this matters - as long as it's a dedicated
> error code, the user can write code to DTRT somehow.  But I don't buy
> your argument.  Ultimately, user activity causes any kind of recovery
> conflict.

Well, yeah, but the predictability of the failure is pretty variable.
In this case we can say that the error definitely would not have
occurred if somebody hadn't done a DROP DATABASE on the master while
there were live sessions in that DB on the slave.  I think that's a
sufficiently close coupling to say that the error is the result of an
operator action.  OTOH, the occurrence of deadlocks is (usually) a lot
more dependent on random-chance timing of different transactions, and
you usually can't point to any action that intentionally caused a
deadlock.

> Then again - in theory, there's no reason why we couldn't drop a
> database on the master when it's in use, kicking out everyone using it
> with this very same error code.  We don't happen to handle it that way
> right now, but...

Yeah, that was in the back of my mind too.  "DROP DATABASE foo FORCE",
maybe?

			regards, tom lane

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