Month: April 2011

Client-failover for dataguard switchover and failover


Introduction

The following is nothing more than some extension of the oracle metalink document:

[ID 740029.1] Step By Step Guide On How To Configure And Test Client-Failover For Dataguard Switchover And Failover

That is, the article does not only present the cookbook how-to of its anchestor but also examines what happens in the database and what the clients experience will be concerning a so called transparent application failover (TAF). The scenario has been tested on an oracle 10.2.0.3 on windows, please note that the metalink document points to a some more applicable technique available with oracle 11gR2 (Client Failover Best Practices for Highly Available Oracle Databases: Oracle Database 11g Release 2).

Client-failover for dataguard, away from other failover scenarios, essentially aims at using a general tnsnames entry against some server-side database endpoint, no matter what server-side database instance is currently running in a dataguard primary role. This is actually the transparency in a transparent application failover where the application, client here, does not have to care to switch its network configuration in any way (some simple implementation would be, not uncommonly, to provide some tnsnames.ora, tnsnames.ora.prm and tnsnames.ora.stb and rename the files) during a failover or switchover.

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Materialized views ddl and dml stati (and the infamous NEEDS_COMPILE)


introduction

Employing materialized views (or snapshot or mview for short) for producing simple sum-up reports is really cool stuff. You just launch some statement like below and will be served with a well performing collection of data that is more or less current (that is why i call that simple). Oracle will care for the refresh of the mview by self-registering a job on calling dbms_refresh.refresh('some_mv');, that starts immediately and takes the interval from the statement. Handing in the force keyword just chooses a fast refresh method iff possible and a complete refresh method otherwise. There are more defaults applied by leaving other keywords unset, the refresh mode for example, but this is not the point of the article. It is:

Why does that … mview always show a state of NEEDS_COMPILE although no ddl action has happend along the objects dependency chain lately?

create materialized view some_mv
  build immediate
  refresh force next (sysdate + 1/24/12)
as
select X.ts, Y.name from (
  select to_char(max(A.ts), 'dd.mm.yyyy hh24:mi') as ts, B.blubb
    from tab1 A, tab1_1 B where A.id = B.id
    group by B.blubb
) X, tab2 Y
  where X.blubb = Y.id;

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RFS: No standby redo logfiles …


Some day, you may trap the following error message with your standby database alert log (seen on a 10.2.0.3):

RFS: No standby redo logfiles available

The reason for this message is most probably that you have cloned your standby database with rman and configured your dataguard environment to directly write into redo log at standby (using LGWR), instead of just transfering the archive log items from primary (using ARCH), but have missed to provide the necessary standby redo log files. RFS may also log RFS[1]: Unable to open standby log 9: 313 or something similar (the primary will also complain about connection problems to the standby destination target, which is the standby redo log, actually).

RFS: No standby redo logfiles available of size 104857600 bytes

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