Re: Replication

On Aug 21, 2006, at 15:00 , D'Arcy J.M. Cain wrote:

> On Mon, 21 Aug 2006 14:46:05 -0400
> "Gregory Maxwell" <gmaxwell@gmail.com> wrote:
>> On 8/21/06, Alvaro Herrera <alvherre@commandprompt.com> wrote:
>>> But the confirmation that needs to come is that the WAL changes have
>>> been applied (fsync'ed), so the performance will be terrible.  So  
>>> bad,
>>> that I don't think anyone will want to use such a replication  
>>> system ...
>>
>> Okay. I give up... Why is waiting for fsync on a fast local network
>> which takes 15us to send a message (infiniband is cheap..) an
>> unimaginable delay when we tolerate a local 8ms fsync delay on  
>> systems
>> without writeback cache?
>
> OK, that solves your problem.  How about my problem where replication
> has to happen on servers in three countries on two continents and
> thousands of updates a second have to happen in less that 10ms?  
> This is
> the critical issue with replication - one size does not fit all.
> Syncronous replication, in particular, fits almost no one.
>
> My experience is that any replication needs to be based on your  
> business
> rules which will vary widely.

Sure- and more specifically, replication rules may differ on every  
table according to those rules. The current solutions are on/off for  
a list of tables. I wonder if the various pgsql replication engines  
have any problems co-existing...

-M