From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Aidan Van Dyk <aidan(at)highrise(dot)ca>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Sync Rep for 2011CF1 |
Date: | 2011-01-22 13:31:14 |
Message-ID: | 1295703074.1803.19835.camel@ebony |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Fri, 2011-01-21 at 13:32 -0500, Robert Haas wrote:
> One idea might be to wait both before and after commit. If
> allow_standalone_primary is off, and a commit is attempted, we check
> whether there's a slave connected, and if not, wait for one to
> connect. Then, we write and sync the commit WAL record. Next, we
> wait for the WAL to be ack'd. Of course, the standby might disappear
> between the first check and the second, but it would greatly reduce
> the possibility of the master being ahead of the standby after a
> crash, which might be useful for some people.
I like this idea.
I think it would be too invasive to make a check before we insert each
WAL record, as Aidan suggests. Even if we did that, you aren't protected
when a standby goes down because you'll still have written half a
transaction and still be waiting.
So I propose that
if (!allow_standalone_primary)
ConfirmSyncRepAvailable();
before PreCommit_Notify(). That puts transaction into a wait state that
lasts until a sync rep standby is available. Note that it is before the
actual commit, so if we decide we need to we can cancel those
transactions and have them properly abort.
I won't add that code yet, in case better ideas emerge.
There is no support for preventing connections at startup, so I will
remove that completely, now.
--
Simon Riggs http://www.2ndQuadrant.com/books/
PostgreSQL Development, 24x7 Support, Training and Services
From | Date | Subject | |
---|---|---|---|
Next Message | Robert Haas | 2011-01-22 14:54:53 | Re: auto-sizing wal_buffers |
Previous Message | Pavel Stehule | 2011-01-22 10:32:02 | Re: Re: patch: fix performance problems with repated decomprimation of varlena values in plpgsql |