| 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, running xacts, subtransactions |
| Date: | 2009-02-25 21:05:40 |
| Message-ID: | 1235595940.16176.347.camel@ebony.2ndQuadrant |
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| Lists: | pgsql-hackers |
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.com
PostgreSQL Training, Services and Support
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