I just noticed MobaXterm 8.0 was released a few days go.
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 220.127.116.11 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.
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.
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:
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:
Only after the filesystem is unfreezed using the following command, can it continue:
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:
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.
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 (http://www.oracle.com/technetwork/database/options/clustering/application-continuity-wp-12c-1966213.pdf). 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.
I recently applied system patch 20132450 to my 18.104.22.168.0 installation on a 2 node RAC system on Oracle Linux 7.1. While ensuring that OPatch is the latest version available I came across an interesting command line option in opatchauto. It is called “-generateSteps”.