If your redo log files are normal unix files (i.e. not raw devices
or Veritas quick I/O files, then the first process to read a block
will bring that block into the buffer cache. The second process will
find already in the cache, which might benefit the other guy. I/O
contention seems unlikely. Running into an insufficiently qualified
support person, on the other hand, seems very likely. You can always
use replication to copy things to another instance.
> -----Original Message-----
> From: johanna.doran_at_sungard.com [mailto:johanna.doran_at_sungard.com]
> Sent: Thursday, June 06, 2002 10:32 AM
> To: Multiple recipients of list ORACLE-L
> Subject: RE: I/O contention with external process reading the oracle
> logs (online redo logs)
>
>
> NB_ RESENDING in plain text - sorry, Outlook keeps seinding
> in html no matter what default i set!
> Hi lists,
>
> I am using Quest Shareplex product for Oracle to Oracle
> one way replication. I have two systems (source and target)
> and two environments (dev, demo). On system one, the
> environments are setup as schemas within one oracle instance
> (therefore each schema will be a SOURCE in the replication).
> My other system has each environment set up a separate Orace
> Instances (therefore each instance will become a TARGET in
> the replication).
>
> I am trying to configure 2 separate replication streams
> (ie so that each replication process is SEPARATE from the
> other - one for DEV and one for DEMO). I will accomplish
> this by setting up Shareplex to use mulitple processes.
>
> HOWEVER, Quest technical support has told me that this
> will cause contention. However, I dont see why is would from
> an os/oracle point of view. Basically Shareplex has a
> process which reads the online redo logs......... tech
> support is suggesting that is there a two processes trying to
> access the same block in the logs that contention can occur.
> This does not make sense to me. Below is the blurb from
> techincal support when I questioned their initial repsonse:
>
> **************************************************************
> ***************************************************************
> The reason you might run into a contention is because
> multiple captue processes may be reading the same data block
> in the redo log. Since there is only one process that can
> access a single block, the other process may have to wait.
> Contention is a possibilty, and you will need to run some
> bench marks to find out how much, if any, contention you will have.
> **************************************************************
> ***************************************************************
>
> I would find it HARD to believe that only ONE process can
> read a block at a time. If this were true, then OLTP system
> would FAIL miserably!
>
> Anyone have any ideas/comments regarding the OS and Oracle
> interaction .... I mean are not the logs at this pointa UNIX
> file? and can't multiple processes read a single unix file
> without bringing the whole system to its knees?
> Also, I am NOT knocking the techincal support, but I believe
> that the opinion was formulated on an incorrect assumption on
> the operating system and Oracle.
> Thoughts/comments?
>
> Thanks in advance.
>
> Hannah
>
>
>
>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author:
> INET: johanna.doran_at_sungard.com
>
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INET: MGogala_at_oxhp.com
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Received on Thu Jun 06 2002 - 12:58:28 CDT
