Date: Thu, 23 Jun 2016 18:59:57 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>
Cc: Robert Haas <robertmhaas@gmail.com>,
	Amit Kapila <amit.kapila16@gmail.com>,
	Thomas Munro <thomas.munro@enterprisedb.com>,
	Stephen Frost <sfrost@snowman.net>,
	Michael Paquier <michael.paquier@gmail.com>,
	Masahiko Sawada <sawada.mshk@gmail.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: Reviewing freeze map code
Message-ID: <20160623225957.GA230122@alvherre.pgsql>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20160623224224.ubztdvhfx6bwkphu@alap3.anarazel.de>
User-Agent: Mutt/1.5.23 (2014-03-12)
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

Andres Freund wrote:

> I'm looking into three approaches right now:
> 
> 3) Use WAL logging for the already_marked = true case.


> 3) This approach so far seems the best. It's possible to reuse the
> xl_heap_lock record (in an afaics backwards compatible manner), and in
> most cases the overhead isn't that large.  It's of course annoying to
> emit more WAL, but it's not that big an overhead compared to extending a
> file, or to toasting.  It's also by far the simplest fix.

I suppose it's fine if we crash midway from emitting this wal record and
the actual heap_update one, since the xmax will appear to come from an
aborted xid, right?

I agree that the overhead is probably negligible, considering that this
only happens when toast is invoked.  It's probably not as great when the
new tuple goes to another page, though.

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


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers