Re: pg_basebackup for streaming base backups

On Thu, Jan 20, 2011 at 2:10 PM, Dimitri Fontaine
<dimitri@2ndquadrant.fr> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> I think that the basic problem with wal_level is that to increase it
>> you need to somehow ensure that all the backends have the new setting,
>> and then checkpoint.  Right now, the backends get the value through
>> the GUC machinery, and so there's no particular bound on how long it
>> could take for them to pick up the new value.  I think if we could
>> find some way of making sure that the backends got the new value in a
>> reasonably timely fashion, we'd be pretty close to being able to do
>> this.  But it's hard to see how to do that.
>
> Well, you just said when to force the "reload" to take effect: at
> checkpoint time.  IIRC we already multiplex SIGUSR1, is that possible to
> add that behavior here?  And signal every backend at checkpoint time
> when wal_level has changed?

Sending them a signal seems like a promising approach, but the trick
is guaranteeing that they've actually acted on it before you start the
checkpoint.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company