Tuesday, October 02, 2007

More Online Utilities [DB2 9 for z/OS]

Today we continue our investigation into the new functionality in DB2 9 for z/OS... and specifically into the improvements made to IBM utilities for version 9. We will turn our attention to improved availability with IBM DB2 utilities. Under DB2 V9, three more utilities can run online – that is, with SHRLEVEL CHANGE.

First up we have CHECK DATA. This utility is executed when you want to make sure that the data in your tables matches your integrity constraints. Prior to V9, access to tables (or table spaces) is read only when CHECK DATA is being run. This means that as long as CHECK DATA is executing you cannot modify data. If you have complex referential sets and/or very large databases you likely will have issues with running CHECK DATA.

You can run CHECK DATA online – that means with SHRLEVEL CHANGE – as of DB2 V9. As with other online utilities, an online CHECK DATA will work with on a shadow copy of the data and indexes. DB2 makes the shadow copy using DFSMS ADRDSSU. This copy can be super fast if you have data set level FlashCopy V2 enabled. Even if you do not have FlashCopy availability will improve because the outage is reduced when you use SHRLEVEL CHANGE (just to make the copy) instead of SHRLEVEL REFERENCE (for the entire utility execution).

DB2 will check data integrity using the shadow copies of the data and indexes. When violations are found DB2 will not set the CHECK pending state. And remember, we are checking shadows, so DB2 will not delete rows in violation. Instead, CHECK DATA will create a PUNCHDDN containing REPAIR LOCATE DELETE input that can be run against the active data.

The CHECK LOB utility has also been enhanced to enable online execution. DB2 V9 allows SHRLEVEL CHANGE for checking LOBs using a shadow copy of the LOB table space. And just like CHECK DATA, DB2 uses the DFSMS ADRDSSU utility to create the shadow. And similarly, the check is executed against the shadow and REPAIR statements are generated that you subsequently can run against the actual LOB table space.

Finally, you can also run the REPAIR LOCATE utility specifying SHRLEVEL CHANGE. This enhancements allows us to execute the REPAIR utility online with LOCATE against indexes, index spaces and table spaces.

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