DB2 Virtual Storage – The Journey Continues

(Originally posted 2006-05-15.)

DB2 Version 8 introduced some very significant exploitation of 64-bit virtual storage. It would be naive to believe that was a total conversion to 64-bit and indeed installations’ mileage varies, depending on circumstances. Here are two APARs that show the journey continues…

PK21268 MOVE CURRENT PATH STORAGE OUT OF STACK AND INTO ABOVE BAR

From the APAR Comments: The working storage to hold CURRENT PATH information has been moved to above-the-bar storage. This will reduce below-the-bar storage consumption.

The word stack is significant as it is one area where the conversion to 64-bit was said to increase storage requirements below the bar. You can monitor Stack Storage using IFCID 225 DB2 Statistics Trace records.

PK21237 VIRTUAL STORAGE CONSTRAINT RELIEF IN BUFFER MANAGEMENT

This provides relief in three areas, according to the APAR description…

The buffer manager engines have been modified to use a single common above-the-bar storage pool, rather than having a separate pool for each engine.

Additionally, the default maximum for the number of engines has been reduced.

For both castout engines and P-lock engines, excess stack storage will now be released before suspending awaiting more work to do.