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Re: Hot standby, freezing

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Hot standby, freezing
Date: 2009-11-11 10:35:50
Message-ID: 4AFA9386.5040901@enterprisedb.com (view raw) 
While reading through the patch for what must be the 100th time by now,
it occurred to me that this comment in heap_xlog_freeze:

+       /*
+        * Freezing tuples does not require conflict processing
+        */

is plain wrong. In the master, we can freeze the xmin of a tuple that's
not yet visible to all read-only transactions in the standby. We do need
conflict processing there.

-- 
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com
From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Hot standby, freezing
Date: 2009-11-11 15:07:53
Message-ID: 1257952073.5363.1594.camel@ebony (view raw) 
On Wed, 2009-11-11 at 12:35 +0200, Heikki Linnakangas wrote:
> While reading through the patch for what must be the 100th time by now,

:-)

> it occurred to me that this comment in heap_xlog_freeze:
> 
> +       /*
> +        * Freezing tuples does not require conflict processing
> +        */
> 
> is plain wrong. In the master, we can freeze the xmin of a tuple that's
> not yet visible to all read-only transactions in the standby. We do need
> conflict processing there.

I agree. Hmph, I wonder why I thought otherwise?

-- 
 Simon Riggs           www.2ndQuadrant.com

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