From: | Josh Berkus <josh(at)agliodbs(dot)com> |
---|---|
To: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: 64-bit XIDs again |
Date: | 2015-07-30 21:29:46 |
Message-ID: | 55BA974A.2080208@agliodbs.com |
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Lists: | pgsql-hackers |
On 07/30/2015 07:24 AM, Heikki Linnakangas wrote:
>
> I think we should move to 64-bit XIDs in in-memory structs snapshots,
> proc array etc. And expand clog to handle 64-bit XIDs. But keep the
> xmin/xmax fields on heap pages at 32-bits, and add an epoch-like field
> to the page header so that logically the xmin/xmax fields on the page
> are 64 bits wide, but physically stored in 32 bits. That's possible as
> long as no two XIDs on the same page are more than 2^31 XIDs apart. So
> you still need to freeze old tuples on the page when that's about to
> happen, but it would make it possible to have more than 2^32 XID
> transactions in the clog. You'd never be forced to do anti-wraparound
> vacuums, you could just let the clog grow arbitrarily large
When I introduced the same idea a few years back, having the clog get
arbitrarily large was cited as a major issue. I was under the
impression that clog size had some major performance impacts.
--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com
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