From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
---|---|
To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Latest version of Hot Standby patch |
Date: | 2008-12-18 15:42:34 |
Message-ID: | 1229614954.4793.431.camel@ebony.2ndQuadrant |
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Thread: | |
Lists: | pgsql-hackers |
On Thu, 2008-12-18 at 15:13 +0200, Heikki Linnakangas wrote:
> Can't we use the existing backendid in place of the slot id?
>
> (sorry if this has been discussed already; can't remember)
Exactly the sort of question we need, but unfortunately I'm a little
hazy, but I just woke up some maybe some coffee will change that answer
later.
They're certainly related and I did try it initially. SlotId was not
present in early versions of the patch up to 13 Oct, though backendId
was.
IIRC there were a couple of reasons
* corner case behaviour of backendids - bgwriter writes checkpoint WAL
records. Has no backendid, but needs a slotid (possibly others)
* slotids are assigned once and never changed, so allowing them to be
used as array lookups directly
I think it would be possible to use slotids as backendids, but not the
other way around. Anyway, seemed like a great way to induce bugs into
the sinval code, so I didn't try too hard to make them identical.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
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