Re: speed of light

From: DA Morgan <>
Date: Fri, 06 Jun 2008 10:00:45 -0700
Message-ID: <>

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
> 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

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

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