| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Aidan Van Dyk <aidan(at)highrise(dot)ca>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Sync Rep: First Thoughts on Code |
| Date: | 2008-12-11 15:07:35 |
| Message-ID: | 49412CB7.6010100@enterprisedb.com |
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| Thread: | |
| Lists: | pgsql-hackers |
Simon Riggs wrote:
> On Thu, 2008-12-11 at 09:27 -0500, Aidan Van Dyk wrote:
>
>> But "catchup" *has* to be *done* before PostgreSQL can enter "sync rep".
>
> Not true. Please reread the thread where Heikki questions that and I
> reply. This was Fujii-san's idea, which I now agree with.
I think the confusion here is about what exactly "sync rep" means in
this situation. It's true that you can start streaming the WAL before
the standby has fully caught up. But from the client's point of view,
there's not much point in streaming the log *synchronously* and making
the client to wait for the acknowledment from the standby, if the
acknowledgment from the standby that WAL has be streamed up to point X,
doesn't actually guarantee that the slave can recover all the way to
that point.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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