On Fri, May 30, 2008 at 10:40 AM, Tom Lane <
tgl@sss.pgh.pa.us> wrote:
But since you mention it: one of the plausible answers for fixing the
vacuum problem for read-only slaves is to have the slaves push an xmin
back upstream to the master to prevent premature vacuuming. The current
design of pg_standby is utterly incapable of handling that requirement.
So there might be an implementation dependency there, depending on how
we want to solve that problem.
I think it would be best to not make the slave interfere with the master's operations; that's only going to increase the operational complexity of such a solution.
There could be multiple slaves following a master, some serving data-warehousing queries, some for load-balancing reads, some others just for disaster recovery, and then some just to mitigate human errors by re-applying the logs with a delay.
I don't think any one installation would see all of the above mentioned scenarios, but we need to take care of multiple slaves operating off of a single master; something similar to cascaded Slony-I.
My two cents.
Best regards,
--
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