Re: pg_multixact not getting truncated

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: Greg Stark <stark(at)mit(dot)edu>, Robert Haas <robertmhaas(at)gmail(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_multixact not getting truncated
Date: 2014-11-21 19:20:53
Message-ID: 20141121192052.GP1639@alvin.alvh.no-ip.org
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Josh Berkus wrote:

> Actually, here's a question ... pg_clog is usually smaller than I think
> it should be (that is, smaller than 4bytes * XID_age). Why is that?

It's not 4 bytes per Xid, but 2 bits per Xid, so Xid_age / 4.

--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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