Performance enhancements

The Db2® 11.5.5 release contains performance enhancements that improve queries against column-organized tables.

Attention: This mod pack release is currently available for the following Db2 products:

The following table lists performance enhancements that have been added to Db2 11.5.5:

Table 1. Performance enhancements in 11.5.5
Enhancement	Description
Enhanced query performance against column organized tables	Query performance against column organized tables is further enhanced by key improvements in `GROUP BY` and `JOIN` memory utilization. With this efficient memory utilization enhancement, complex queries on column organized tables can see reduced spill I/O within `GROUP BY` and `JOIN` operations, resulting in improved performance. In particular, `GROUP BY` and `JOIN` queries involving wide value types that have a large percentage of the column values shorter than the defined schema width now show improved performance.
`DEACTIVATE DATABASE` operations may complete faster, in scenarios where these operations occur shortly after a database activation	When database activation occurs and deferred memory commit is enabled (see DB2_DEFER_MEMORY_COMMIT), the initialization of bufferpool and locklist memory is performed asynchronously in the background, which allows database activation to complete and the database to be available for application connections sooner. During the short time-period after database activation while this memory is being initialized in the background, a `DEACTIVATE DATABASE` operation will now complete faster.