Re: CDC using LogMiner in RAC environment

From: Jeffery Thomas <>
Date: Mon, 29 Sep 2008 16:08:43 -0400
Message-ID: <>

I found a note in the 11g doc that is not in the 10g doc set that is pertinent to our situation:

"You should only use CONTINUOUS_MINE on an Oracle RAC database if no thread is being enabled or disabled."

Looking more like CDC based on LogMiner in a RAC environment is not going to function that reliably.


On Mon, Sep 29, 2008 at 11:14 AM, Jeffery Thomas <> wrote:
> Currently, we are using an Informatica product to perform CDC in a
>, two-node RAC environment.
> The product has a listener that receives results from an ad-hoc query
> against V$LOGMNR_CONTENTS in
> continuous mining mode, then ships relevant transactions to a
> different database.
> The process seems somewhat fragile. If we take down one instance for
> maintenance (or if it crashes) the
> LogMiner session ends due to the disabled thread. A mining session
> can also sporadically terminate as a
> result of a hot backup, apparently due to the alter system archive
> log issued by RMAN. There is a known
> bug in RAC (fixed in 11.2) where a LogMiner continuous mining
> session terminates due to a disabled
> thread that we are discussing with Support.
> There's no filtering of redo by the ad-hoc query, the SELECT has no
> WHERE. The business logic is outside
> the database in the Informatica piece so that all redo records mined
> are forwarded to the external 3rd-party
> listener. So in a busy source database there can be a considerable
> lag between the time of the commit of a
> relevant transaction to when it gets shipped to the target database.
> My question(s) would be: is LogMiner alone onsidered sufficiently
> robust and reliable to provide near real-time CDC?
> Is it intended to be used in that fashion where the usage is simply an
> un-filtered ad-hoc select against
> V$LOGMNR_CONTENTS in continuous mining mode and shipping the data
> outside to an external 3rd-party
> tool?
> Reading about LogMiner in the Oracle docs does not mention CDC per
> se, only identifying it as a tool for auditing
> and data analysis. If we were to use Streams which seems to be the
> recommended Oracle CDC mechanism and
> that also uses LogMiner under the hood, would we see the same
> fundamental issues as we are currently
> experiencing?
> Thanks,
> Jeff

Received on Mon Sep 29 2008 - 15:08:43 CDT

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