Re: Symetric Replication Anyone?

In article <32663728.3CA6_at_realworld.com>, Gary Eckhardt <gary_eckhardt_at_realworld.com> writes
>Mike Lacey wrote:
>>
>> What experiences do people have with Symetric
>> Replication?
>>
>> This is what I'm considering:
>>
>> Central site with with an rs6000 running Oracle
>> V7.2.6.0.2
>>
>> Remote sites (currently with horrible performance
>> problems) connected via a 64k leased line with NW
>> 3.12 servers running Oracle 7.something.
>>
>> Some tables would be replicated at the remote
>> sites.
>>
>> I've not "done" replication before and I'd value
>> everyones comments.
>
>I'm currently involved in a project that involves a master site,
>a backup master site, and several (24) snapshot sites. Here's just
>a few issues off the top of my head:
>
>1) On your master database, put as much memory as you can.
> Then try to get some more. Seriously, with all these
> sites, we experienced a multitude of memory problems with
> the system swapping continuously. The more sites you add,
> the busier your system is going to be.
>
>2) Plan your database carefully, especially your snapshot sites,
> and your update times. We are currently running with a
> 5 minute update on some tables and 30 second updates on others.
>
>3) If you are running archive log on your master database, be
> prepared to allocate a lot of disk space. Our log switch rate
> on a database that is currently doing NOTHING is about once
> every 3-5 minutes.
>
>4) As much as Oracle would like it to be, the replication system
> is not trivial, and you will need to study the manuals
> carefully. There are a lot of stored procedures, etc. that
> need to be run to set up your replicated schema. The
> Replication Manager in the Oracle Enterprise Manager pack is
> a step in the right direction, but it still is limited.
> Plus, as in any Oracle manual, procedures don't always look/act
> the way they're advertised.
>
>5) If you can, upgrade to the most version of Oracle (7.3). There
> were known replication problems in 7.2. If/When you do upgrade,
> make sure you link in the Spatial Data Option, as there was
> a problem with 7.3 using database links, and that was the
> work-around.
>
>
>Oracle replication works surprisingly well when it is all up and
>running, but just be careful in what you do!

I would agreed with the above. Don't underestimate the hassle of getting it to work. Some other considerations are :

Check that there is no conflict with your application, in particular 'active' triggers that change columns before inserts/updates will cause big problems.

How are you going to synchronise password changes between the two databases?

If you are using synchronous / symmetric replication then the speed of your link is even more important.

If using synchronous / asymmetric replication how will your application deal with lost data?

-- 
Chris Dipple, Production DBA, Royal Bank of Scotland