Horton

Re: pg_basebackup for streaming base backups

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Dimitri Fontaine <dimitri@2ndquadrant.fr>
Cc: Bruce Momjian <bruce@momjian.us>, Magnus Hagander <magnus@hagander.net>, Simon Riggs <simon@2ndquadrant.com>, Tom Lane <tgl@sss.pgh.pa.us>, Peter Eisentraut <peter_e@gmx.net>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2011-01-20T19:51:27Z
Lists: pgsql-hackers 
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
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