Re: Geographic High-Availability/Replication

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On 08/24/07 08:21, Markus Schiltknecht wrote:
> Hi,
>
> Matthew wrote:
>> Hey all, new postgres user here. We are trying to setup/research an
>> HA/Replicated solution with Postrgresql between a datacenter in LA and a
>> d.c. in NY.
>>
>> We have a private LAN link between the two D.C.'s with a max round-trip
>> of 150ms.
>>
>> We will have a web server at each d.c. (among other servers) that will
>> write/read to/from the local LAN DB. On writes, that data should be
>> xmited to the other data center so that if, for whatever reason, my
>> website request was sent to LA instead of NY, all my session information
>> etc will still exist.
>
> This is commonly known as synchronous replication. As that involves
> *at-least* one round-trip *before* committing, it's quite expensive. Can
> you live with a delay of ~150ms before COMMIT confirmation?

Which puts an upper limit on transaction rates at 6TPS. Blech.

> Another issue is the reliability of your failure detectors. How does
> server B know that server A is really down (and not only the link?).
> Normally, that's solved with a quorum device. So that you have to have
> at least three servers - preferably in different locations.

- --
Ron Johnson, Jr.
Jefferson LA USA

Give a man a fish, and he eats for a day.
Hit him with a fish, and he goes away for good!

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