Re: Hot standby, running xacts, subtransactions

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.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support