Re: Is there a peer-to-peer server solution with PG? - Mailing list pgsql-general

Martha Stewart called it a Good Thing when nolan@gw.tssi.com (Mike Nolan) wrote:
>> Slony-1 is perfectly capable of replicating to a slave database,
>> then letting you decide to promote it to master, which is just what
>> you'd need.  Why are you asking about multi-master?
>
> I am concerned that if I have to support the traffic to keep the
> slave unit in sync PLUS support general database use from the
> 'slaved' office to the master one, on the same comm line, I might
> start running into congestion issues.
>
> We will have people actively working the database in both office for
> a period of several weeks to several months, depending on how the
> final transfer plan unfolds.
>
> Master/Slave is probably an acceptable solution, I was just
> wondering if there was a multi-master one available yet.

There is an effort under way; in planning stages at this point.  Don't
expect that to be "productized" next month...

Let me wag a finger at one of your assumptions...

You should re-examine assumptions with great care if you start
imagining that you'll get more throughput out of a general purpose
"multimaster" system.  (Something designed specifically for your
application is quite another matter, particularly if your application
turns out to be, in some fashion "embarassingly parallelizable.")

Synchronization can't _conceivably_ come for free; it has _got_ to
have some cost in terms of decreasing overall performance.

If you have so much update load that one server cannot accomodate that
load, then you should wonder why you'd expect that causing every one
of these updates to be applied to (say) 3 servers would "diminish"
this burden.

Each of the 3 servers may only have to take on 1/3 of the updates from
the outside, but they surely have to accomodate the other 2/3 as well.

This not to say that there can't be some benefits from multimaster
replication; that's why such projects are proceeding.

But it's NOT a panacea; it's NOT an easy "general purpose solution."

I was in a room with The Thinkers; I got the sense that the lights
dimmed for blocks around when they put their thinking caps on :-).  To
this group of Rather Smart Folk, perceiving the array of concurrency
and locking problems required great attention on their part.  'Easy'
is definitely not the right word...
--
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