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Re: Hot Standby query cancellation and Streaming Replication integration

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Richard Huxton <dev(at)archonet(dot)com>, Greg Smith <greg(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Hot Standby query cancellation and Streaming Replication integration
Date: 2010-02-26 17:45:33
Message-ID: 603c8f071002260945t82f6f3dt67ceca34ba9f9287@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Fri, Feb 26, 2010 at 10:21 AM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> Richard Huxton wrote:
>> Can we not wait to cancel the transaction until *any* new lock is
>> attempted though? That should protect all the single-statement
>> long-running transactions that are already underway. Aggregates etc.
>
> Hmm, that's an interesting thought. You'll still need to somehow tell
> the victim backend "you have to fail if you try to acquire any more
> locks", but a single per-backend flag in the procarray would suffice.
>
> You could also clear the flag whenever you free the last snapshot in the
> transaction (ie. between each query in read committed mode).

Wow, that seems like it would help a lot.  Although I'm not 100% sure
I follow all the details of how this works.

...Robert

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