From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Simon Riggs <simon@2ndQuadrant.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Visibility map, partial vacuums
Date: Tue, 28 Oct 2008 14:57:13 +0200
Message-ID: <49070C29.9090508@enterprisedb.com> (raw)
In-Reply-To: <1225193108.3971.154.camel@ebony.2ndQuadrant>
References: <4905AE17.7090305@enterprisedb.com>
<1225193108.3971.154.camel@ebony.2ndQuadrant>
Simon Riggs wrote:
> On Mon, 2008-10-27 at 14:03 +0200, Heikki Linnakangas wrote:
>> One option would be to just ignore that problem for now, and not
>> WAL-log.
>
> Probably worth skipping for now, since it will cause patch conflicts if
> you do. Are there any other interactions with Hot Standby?
>
> But it seems like we can sneak in an extra flag on a HEAP2_CLEAN record
> to say "page is now all visible", without too much work.
Hmm. Even if a tuple is visible to everyone on the master, it's not
necessarily yet visible to all the read-only transactions in the slave.
> Does the PD_ALL_VISIBLE flag need to be set at the same time as updating
> the VM? Surely heapgetpage() could do a ConditionalLockBuffer exclusive
> to set the block flag (unlogged), but just not update VM. Separating the
> two concepts should allow the visibility check speed gain to more
> generally available.
Yes, that should be possible in theory. There's no version of
ConditionalLockBuffer() for conditionally upgrading a shared lock to
exclusive, but it should be possible in theory. I'm not sure if it would
be safe to set the PD_ALL_VISIBLE_FLAG while holding just a shared lock,
though. If it is, then we could do just that.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: heikki.linnakangas@enterprisedb.com, simon@2ndQuadrant.com
Subject: Re: Visibility map, partial vacuums
In-Reply-To: <49070C29.9090508@enterprisedb.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox