Re: replication/synchronisation

glenn(at)tangelosoftware(dot)net (Glenn Davy) writes:
> Hey Chris
> Thanks for replying
>
>> Unfortunately, the "usual suspects" are generally designed to work
>> when systems are connected more or less all the time.
>>
> yep - thats true
>> Furthermore, what you're after seems to be one of the forms of
>> "multimaster" replication,
> yes that would make sense
>
>> which is the tougher problem that generally
>> isn't supported.
>>
> just wondering what you mean by 'generally'?

None of the "product-like" things like Slony-I, Mammoth Replicator,
and such support multimaster replication.

>> In effect, what you're trying to do is akin to what PalmOS and Lotus
>> Notes solve using synchronization systems. There aren't any tools I
>> can readily point you to to help do this with PostgreSQL, alas.

> ok thanks - Im wondering how microsoft access and mssql server seem
> to achieve this so easily - it seems to be tied up with that
> massively long alpha unique row id (uid?) i wonder if adding similar
> fields (ensuring uniqueness could prove interesting) to all tables
> in any given schema and triggers or rules to maintain them would
> allow provide a basis for some sort of simple system? Im clearly out
> of my depth here - just puzzled why it seems so doable in some
> platforms and nigh impossible on others.
>
> I guess im wondering if there is something intrinsic to postgres that
> makes this idea prohibitive, or is it that developers already have hands
> full with other features on their minds?

Conflict resolution is the Big Problem with asynchronous multimaster
replication.

Nobody has a direct answer to it. People try to design schemas to
avoid conflicts as much as possible.

When conflicts occur, a DBA has to do something manual, figuring out
what the problem was and how to fix it.

Microsoft has spent a lot of developer time on tools to cover this
over.
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