5486LPOpS.fm Draft Document for Review October 18, 2004590 IBM Eserver i5 and iSeries System HandbookOS/400 High Availability Journal Performance (5722-SS1 Option 42)For V5R2, there are several improvements and additions to journal management.For the most demanding high-availability clustering environments supported byour high availability Business Partners, Journal Standby Mode andAsynchronous Journaling capabilities enable faster failover and reduceperformance bottlenecks. Both the Journal Caching feature and the JournalStandby feature are provided by installing OS/400 option 42.Journal Caching featureThe Journal Caching feature was available as PRPQ 84486 before V5R2 and isnow a standard orderable feature in V5R2. This feature allows batch applicationsto substantially reduce the number of synchronous disk write operationsperformed, thereby reducing overall elapsed batch execution time.Journal Caching provides significant performance improvement for batchapplications that perform large numbers of add, update, or delete operationsagainst journaled objects. Applications using commitment control see lessimprovement (commitment control already performs some Journal Caching).Journal caching is especially useful for situations where journaling is being usedto enable replication to a second system.Journal Standby featureYou may want to put a journal in standby state if the journal is on a backupsystem. By having the journal in standby state, a switchover to the target systemcan be accomplished more quickly because all objects on the backup system canbe journaled, therefore allowing the switchover processing to skip the costly stepof starting journaling for all objects. At the same time, the backup system doesOS/400 - High Availability Journal Performance (5722-SS1 Option 42)Included in base NoStatus Charged featureKeyed - YesRelated productsFurther informationImportant: We recommend that you do not use Journal Caching if it isunacceptable to lose any recent change in the event of a system failure wherethe contents of main memory are not preserved. This type of journaling isdirected toward batch jobs. It may not be suitable for interactive applicationswhere single system recovery is the primary reason for using journaling.
