Re: Replication Options

Hi Rajesh,
On Thu, 2005-02-03 at 18:29, Rajesh.Rao_at_jpmchase.com wrote:

> Hello All,
>
> We have an application that's presently on 9.2.0.5 on a Solaris 8 box. We
> are looking to have a DR / Standby site for this database at a remote
> location. Logical Standby database and Advanced replication were ruled out
> because of the use of LONG and LONG RAW datatypes, and the use of IOT's by
> the database. So, we decided on a physical standby database.

Right choice. Logical (LSB) isn't that much usable as standby, it's more for offloading reporting load from your primary. Physical Standby (PSB) is the way to go for keeping your data safe.

>
> But now, the requirements change, in that, the user wants a ACTIVE/ACTIVE
> configuration. In all sense, its a RAC database with nodes at different
> physical locations. I read, that 10g supports LONG and LONG RAW datatypes
> for Logical standby.

I haven't tested LSB with 10g yet. Don't know whether it has improved a lot. It's still vulnerable to 'illegal' transactions, which will stop the SQL Apply proces.

>
> My questions are:
> 1. Does Oracle support LONG datatypes with Advanced Replications in 10g?

No idea. Advanced Replication adds a whole new dimension when you want active/active. Either you do it with synchronous replication, and both databases will stop when one fails, network latency will slow down your transactions, together with the 2PC, or you do it asynchronously, and end up with a huge bunch of conflict resolution functions. It will be hard to manage and might affect your uptime in a negative way. Of course the users will say that they use perfectly partioned data, never use/change 'each other's' data and conflicts in the replication will not occur. Nevertheless, they will occur, sooner (probably) or later.

> 2. What options do I have? Any third party applications? (Shareplex?)

Is quite expensive.

Requirements for DR stuff is not just a couple of lines. Mostly it takes some days of discussions and meetings to get them clear. Then you can decide what requirements are hard and soft. Then options can be selected.

Shareplex is (very) expensive, and not exactly scalable to any level you might need. Neither is advanced replication. PSB scales quite well, depending on the log transport options chosen and the network bandwith/latency. You can think of PSB for DR purposes, and LSB for offloading reports. Using streams for offloading report work to another database is another option, maybe even better than LSB.

Keep in mind that Logical Standby and Streams require supplemental logging. This can affect your amount of redo genereated quite seriously and thus hurt the performance of your primary database. Furthermore, some SQL apply processes can do the work in parallel, but it might also create a serialization point in your replication mechanism, both with LSB and Streams.

I think the goals to achive need to be specified clearly. They shouldn't be mixed. HA is not something that comes for free. People tend to try to make the 'inactive standby' useful somehow. That interferes with the original requirement. Keep the goals clear and separated.

Best regards,

Carel-Jan Engel

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>
> Thanks
> Raj
>
>
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