Journal management and system performance

 

Journal management prevents transactions from being lost if your system ends abnormally or has to be recovered. Journal management writes changes to journaled objects immediately to the journal receiver in auxiliary storage. Journaling increases the disk activity on your system and can have a noticeable affect on system performance.

Journaling also increases the overhead associated with opening objects and closing objects, so as the number of objects you are journaling increases, the general performance of the system can be slower. The time it takes to perform an IPL on your system or vary on of an independent auxiliary storage pool (ASP) can also increase, particularly if your system or independent ASP ends abnormally.

The system takes measures to minimize the performance effect of using journaling features. For example, the system packages before-images and after-images, and any access path changes for a record in a single write operation to auxiliary storage. Therefore, journaling access paths, and before-images and after-images, usually does not cause additional performance overhead. However, they do add to the auxiliary storage requirements for journaling.

The system also spreads journal receivers across multiple disk units to improve performance. If you do not specify a maximum receiver-size option, then the system can place the journal receiver on up to ten disk units in a disk pool. If you specify a maximum receiver-size option, and a matching sufficiently large journal size threshold then the system can place the journal receiver on up to 100 disk units in a disk pool.

You can take measures to minimize the effect of journaling on your system performance:

 

Parent topic:

Journal management concepts

Related concepts
Receiver size options for journals Journal cache Frequently asked questions about journaling and disk arm usage Performance Disk management Striving for Optimal Journal Performance on DB2 Universal Database for iSeries Factors that affect remote journal performance