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Re: Hot standby, running xacts, subtransactions

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: Re: Hot standby, running xacts, subtransactions
Date: 2009-02-25 21:08:41
Message-ID: 49A5B359.1090908@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Simon Riggs wrote:
> On Wed, 2009-02-25 at 22:39 +0200, Heikki Linnakangas wrote:
> 
>> When we take the snapshot of running transactions in the master, in 
>> GetRunningTransactionData(), it only includes top-level xids and those 
>> subxids that are in the subxid caches. Overflowed subxids are not 
>> included. Isn't that a problem? When the standby initializes the 
>> recovery procs using the running xacts information, pg_subtrans doesn't 
>> isn't set for the overflowed xids, because that information is not 
>> included in the WAL record. If you're lucky, the information is there 
>> already, but we don't generally guarantee pg_subtrans to survive crash 
>> or restart.
> 
> That is exactly the reason why we don't treat an overflowed snapshot as
> a valid starting point.

We don't? I don't see anything stopping it.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

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Subject: Re: Synchronous replication & Hot standby patches
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