Re: speed of light

From: DA Morgan <damorgan_at_psoug.org>
Date: Fri, 06 Jun 2008 10:00:45 -0700
Message-ID: <1212771642.769369@bubbleator.drizzle.com>


kerravon wrote:
> We have an Oracle 9 (soon 10) on Solaris 8 system located in
> Australia,
> and a backup system located in the US. Due to the speed of light,
> there
> is a 400 ms round trip.
>
> Ideally we would like to use DA (line by line) replication from
> Australia to
> the US, but for some reason that is being affected by the round trip
> time.
> My guess is that DA is designed to send one bit of data at a time, and
> thus waits for a response before sending the next bit of data.
>
> Is there any option to get DA to do one of:
>
> 1. While waiting for acknowledgement from remote, queue data and
> then send all the queued data in one hit.
>
> 2. Have multiple threads of execution, sending data off while waiting
> for a response.
>
> 3. Have the remote database as an NFS mount so that Oracle thinks
> it is writing locally and passes the data to Unix. Unix immediately
> acknowledges the write request and then sends of the multiple writes
> to the remote.
>
>
> Currently we are using Oracle Dataguard to cause the data to be
> sent to the remote in batches. That does work, ie it can keep up
> with the transaction flow, but unfortunately means that the remote
> database lags 10-20 minutes behind the master. I don't understand
> why this should be the case. Would a 400 msec round trip explain
> that? Or is this a "feature" of Dataguard?
>
>
> We are about to write an application to do the replication ourselves,
> which will read multiple rows from the appropriate application tables,
> compress the data, write to a table once/minute with the batched
> data, let Oracle DA replicate that one table, 400 msec response is
> irrelevant, then have a daemon to decompress the data the other
> end and populate the relevant application tables.
>
> To my mind, this seems the wrong solution to the problem, and the
> utilities should be able to cope with the speed of light limits.
>
> But I'm not the DBA so can't advise on any 3rd party utilities etc
> that
> would do the job.
>
> It would be great if someone here could give me some advice, or point
> me to where I could get that advice.
>
> If you want to email me, please use mutazilah at
> gmail.com rather than this email address. Replying in the group is
> preferred though.
>
> Thanks. Paul.

Not sure what you mean by DA but with respect to your round trip time have you tuned Oracle's use of TCP/IP?

Among the changes you can make that will significantly affect network performance are the SEND_BUF_SIZE, RECV_BUF_SIZE, and SDU: The later of which should be set to 32767.

I've demos using this in Morgan's Library under Data Guard and you will find these changes well documented at http://tahiti.oracle.com.

-- 
Daniel A. Morgan
Oracle Ace Director & Instructor
University of Washington
damorgan_at_x.washington.edu (replace x with u to respond)
Puget Sound Oracle Users Group
www.psoug.org
Received on Fri Jun 06 2008 - 12:00:45 CDT

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