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Little things worth knowing: Data Guard Broker Setup changes in 12c

One of the problems I have seen when deploying Data Guard for systems such as RAC One Node and policy managed databases was the static listener configuration you needed in 11.2. This has changed with 12c for the better if you are using Grid Infrastructure.

In the section about static listener registration a little addendum can be found (thanks to Patrick Hurley/@phurley for pointing this out to me!):

“A static service needs to be defined and registered only if Oracle Clusterware or Oracle Restart is not being used.”

This is good news, let’s put it to the test; I’m a great fan of Oracle Restart. If I ever find the time I’d like to repeat this test with clustered Grid Infrastructure. I think the quote mentioned earlier still stands true but I would like to see it with my own eyes.

MobaXterm 8.0

command-promptI just noticed MobaXterm 8.0 was released a few days go.

Downloads and changelog available in the usual places.

Happy unzipping!



MobaXterm 8.0 was first posted on July 24, 2015 at 3:19 pm.
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Oracle 12 and latches

Oracle DBAs who are so old that they remember the days before Oracle 11.2 probably remember the tuning efforts for latches. I can still recall the latch number for cache buffers chains from the top of my head: number 98. In the older days this was another number, 157.

But it seems latches have become less of a problem in the modern days of Oracle 11.2 and higher. Still, when I generate heavy concurrency I can see some latch waits. (I am talking about you and SLOB mister Closson).

I decided to look into latches on Oracle instance on Oracle Linux 7. This might also be a good time to go through how you think they work for yourself, it might be different than you think or have been taught.

How long does a logical IO take?

This is a question that I played with for a long time. There have been statements on logical IO performance (“Logical IO is x times faster than Physical IO”), but nobody could answer the question what the actual logical IO time is. Of course you can see part of it in the system and session statistics (v$sysstat/v$sesstat), statistic name “session logical reads”. However, if you divide the number of logical reads by the total time a query took, the logical IO time is too high, because then it assumed all the time the query took was spend on doing logical IO, which obviously is not the case, because there is time spend on parsing, maybe physical IO, etc. Also, when doing that, you calculate an average. Averages are known to hide actual behaviour.

fsfreeze in Linux

The fsfreeze command, is used to suspend and resume access to a file system. This allows consistent snapshots to be taken of the filesystem. fsfreeze supports Ext3/4, ReiserFS, JFS and XFS.

A filesystem can be frozen using following command:

#cccccc;line-height: 1.4"># /sbin/fsfreeze -f /data

Now if you are writing to this filesystem, the process/command will be stuck. For example, following command will be stuck in D (UNINTERUPTEBLE_SLEEP) state:

#cccccc;line-height: 1.4"># echo “testing” > /data/file

Only after the filesystem is unfreezed using the following command, can it continue:

Quick Tip : Oracle User Ulimit Doesn’t Reflect Value on /etc/security/limits.conf

So the other day I was trying to do a fresh installation of a new Oracle EM12cR4 in a local VM,  and as I was doing it with the DB 12c, I decided to use the Oracle preinstall RPM to ease my installation of the OMS repository database. Also I was doing both the repository and EM12c OMS install in the same VM, that is important to know.

[root@em12cr4 ~]# yum install oracle-rdbms-server-12cR1-preinstall -y

I was able to install the DB without any issues, but when I was trying to do the installation of EM12cR4, an error in the pre-requisites popped up:

WARNING: Limit of open file descriptors is found to be 1024.

For proper functioning of OMS, please set “ulimit -n” to be at least 4096.

And if I checked the soft limit for the user processes , it was set to 1024:

Little things worth knowing: Is there a penalty in establishing a connection to Oracle using the MAA connection string? Part 2

In the very lengthy previous post about the MAA connect string I wanted to explain the use of the MAA connection string as promoted by Oracle. I deliberately kept the first part simple: both primary and standby cluster were up, and although the database was operating in the primary role on what I called standby cluster (again it’s probably not a good idea to include the intended role in the infrastructure names) there was no penalty establishing a connection.

Little things worth knowing: Is there a penalty in establishing a connection to Oracle using the MAA connection string?

Sorry for the long title!

I had a question during my session about “advanced RAC programming features” during the last Paris Oracle Meetup about the MAA connection string. I showed an example taken from the Appication Continuity White Paper ( Someone from the audience asked me if I had experienced any problems with it, such as very slow connection timeouts. I haven’t, but wanted to double-check anyway. This is a simplified test using a sqlplus connection since it is easier to time than a call to a connection pool creation. If you know of a way to reliably do so in Java/UCP let me know and I’ll test it.