From: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
---|---|
To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
Cc: | Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: New trigger option of pg_standby |
Date: | 2009-03-30 02:32:36 |
Message-ID: | 3f0b79eb0903291932r61d57921v88fea03d46d37c92@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Hi,
On Fri, Mar 27, 2009 at 9:49 PM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> Uh oh, that's going to be quite tricky with signals. Remember that
> pg_standby is called for each file. A trigger file persists until it's
> deleted, but a signal will only be received by the pg_standby instance that
> happens to be running at the time.
You are right!
> Makes me wonder if the trigger pg_standby with signals is reliable to begin
> with. What if the backend is just processing a file when the signal is
> fired, and there's no pg_standby process running at the moment to receive
> it? Seems like the signaler needs to loop until it has successfully
> delivered the signal to a pg_standby process, which seems pretty ugly.
>
> Given all the recent trouble with signals, and the fact that it's
> undocumented, perhaps we should just rip out the signaling support from
> pg_standby.
So far, to be frank, I was not sure why the trigger by the signal is necessary
for pg_standby. But, now, I think that it's useful when the user has forgotten
to specify the trigger file. In this case, without the signaling
support, there is
no way to do failover in a short time; probably, the user has to do shutdown
and restart a recovery from the last restart point, which would take time.
So, I'd like to leave the signaling support as a safeguard.
As you pointed out, the "smart" failover by signal would be very tricky. So,
maybe we should not change the existing behavior of pg_standby when
the signal is received.
Regards,
--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center
From | Date | Subject | |
---|---|---|---|
Next Message | Andrew Gierth | 2009-03-30 03:15:03 | Re: TupleTableSlot API problem |
Previous Message | Alvaro Herrera | 2009-03-30 02:01:03 | Re: Re: [COMMITTERS] pgsql: Temporarily (I hope) disable flattening of IN/EXISTS sublinks |