Re: [SPAM] Re: Best way to replicate to large number of nodes

On 2010-04-22, Brian Peschel <brianp(at)occinc(dot)com> wrote:
>
> On 04/22/2010 10:12 AM, Ben Chobot wrote:
>> On Apr 21, 2010, at 1:41 PM, Brian Peschel wrote:
>>
>>
>>> I have a replication problem I am hoping someone has come across before and can provide a few ideas.
>>>
>>> I am looking at a configuration of on 'writable' node and anywhere from 10 to 300 'read-only' nodes. Almost all of these nodes will be across a WAN from the writable node (some over slow VPN links too). I am looking for a way to replicate as quickly as possible from the writable node to all the read-only nodes. I can pretty much guarantee the read-only nodes will never become master nodes. Also, the updates to the writable node are bunched and at known times (ie only updated when I want it updated, not constant updates), but when changes occur, there are a lot of them at once.
>>>
>> Two things you didn't address are the acceptable latency of keeping the read-only nodes in sync with the master - can they be different for a day? A minute? Do you need things to stay synchronous? Also, how big is your dataset? A simple pg_dump and some hot scp action after you batched updates might be able to solve your problem.
>
> Latency is important. I would say 10 to 15 minutes max, but the shorter
> the better. I don't have an exact size, but I believe the entire DB is
> about 10 gig.

should not be a problem 10 to 15 second latency is easy to get over
slow connections (eg satellite) with any of the proposed solutions.

> We had an idea of creating our apps write the SQL statements to a file,
> rather than using an ODBC drive to directly change the DBs. Then we
> could scp/rsync the files to the remote machines and execute them
> there. This just seems like a very manual process though.

yes, and furthermore SQL-replication tends not to work as intended
if you have any updates or inserts that invoke non-constant default
values like now(), nextvalue(...), or random()