From: | Robert Treat <xzilla(at)users(dot)sourceforge(dot)net> |
---|---|
To: | pgsql-hackers(at)postgresql(dot)org |
Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
Subject: | Re: Hot standby and b-tree killed items |
Date: | 2008-12-20 00:29:16 |
Message-ID: | 200812191929.16606.xzilla@users.sourceforge.net |
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Lists: | pgsql-hackers |
On Friday 19 December 2008 05:52:42 Simon Riggs wrote:
> BTW, I noticed the other day that Oracle 11g only allows you to have a
> read only slave *or* allows you to continue replaying. You need to
> manually switch back and forth between those modes. They can't do
> *both*, as Postgres will be able to do. That's because their undo
> information is stored off-block in the Undo Tablespace, so is not
> available for standby queries. Nice one, Postgres.
>
I think this is true for physical replay, but Oracle also offers the option to
do logical replay (where transaction logs are converted into sql and run
against the standby; i believe this is similar to what continuant is trying
to do with thier latest offering). In that scenario you can do read and
replay at the same time, though I think there are some conflicts possible;
fewer than what postgres will have, since I think most of thier DDL can be
done online. (This might require some extra modules / high end version of
Oracle, please consult your local Oracle wizard for more details)
--
Robert Treat
Conjecture: http://www.xzilla.net
Consulting: http://www.omniti.com
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