| 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 |
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| 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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