Re: Sync Rep: First Thoughts on Code

* Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> [081211 10:09]:
> 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.

Quite possibly a terminology problem.. I my case I said "sync rep"
meaning the mode such that the transaction doesn't commit successfully
for my PG client until the xlog record has been "streamed" to the
client... and I understand that at his presentation at PGcon, Fujii-san
there could be possible variants on when the "streamed" is considered
done based on network, slave ram, disk, application, etc.

a.

-- 
Aidan Van Dyk                                             Create like a god,
aidan@highrise.ca                                       command like a king,
http://www.highrise.ca/                                   work like a slave.