Posts tagged Linux
Recently we noticed that imageinfo was displaying the following information at a customers site. Imageinfo was not displaying data i suspected, so a quick little blogpost about what was going on there.
Recently I am involved in a project which requires a lot of data to be extracted from Oracle. The size of the data was so huge that the filesystems filled up. Compressing the output (using tar j (bzip2) or z (gzip)) is an obvious solution, but this can only be done after the files are created. This is why I proposed compressing the output without ever existing in uncompressed form.
When you are administering an Exadata or more Exadata’s, you probably have multiple databases running on different database or “computing” nodes. In order to understand what kind of IO you are doing, you can look inside the statistics of your database, and look in the data dictionary what that instance or instances (in case of RAC) have been doing. When using Exadata there is a near 100% chance you are using either normal redundancy or high redundancy, of which most people know the impact of the “write amplification” of both normal and high redundancy of ASM (the write statistics in the Oracle data dictionary do not reflect the additional writes needed to satisfy normal (#IO times 2) or high (#IO times 3) redundancy). This means there might be difference in IOs between what you measure or think for your database is doing, and actually is done at the storage level.
Exadata gets its performance by letting the storage (the exadata storage server) participate in query processing, which means part of the processing is done as close as possible to where the data is stored. The participation of the storage server in query processing means that a storage grid can massively parallel (depending on the amount of storage servers participating) process a smart scan request.
The purpose of this post is to show what the wait event ‘cell smart table scan’ means, based on reproducible investigation methods.
This is a quick post about how you can get the debuginfo packages on your Oracle Linux system in the easiest way thinkable: via yum.
This post is about database writer (dbwr, mostly seen as dbw0 nowadays) IO.
The testenvironment in which I made the measurements in this post: Linux X64 OL6u3, Oracle 220.127.116.11 (no BP), Clusterware 18.104.22.168, ASM, all database files in ASM. The test environment is a (VMWare Fusion) VM, with 2 CPU’s.
This post is about log writer (lgwr) IO.
It’s good to point out the environment on which I do my testing:
Linux X64 OL6u3, Oracle 22.214.171.124 (no BP), Clusterware 126.96.36.199, ASM, all database files in ASM.
I have seen several clients who are struggling to decode page allocation failures on Exadata, in this post i will try to explain how to read the backtrace. The following is an anonymized client case where page allocation failures are leading up to a node reboot.