I/O Activity reports

Db2 system performance is heavily influenced by the volume and speed of input activities and output activities. OMEGAMON for Db2 PE provides several summary and detail I/O Activity reports that you can use to analyze I/O activities.

Generally, an I/O Activity report groups the I/O activities in report blocks as follows:
  • The Active Log block shows the number of read and write requests to and from the active log data set and the associated wait times.
  • The Archive Log block shows the number of read and write requests to and from the archive log and the associated wait times.
  • The Bootstrap Data Set block shows the number of read and write requests to and from the bootstrap data set (if present). The bootstrap data set also controls the movement of data from the active log to the archive log data sets.
  • The Buffer Pool block shows the number and types of read and write requests to and from the buffer pools and the associated wait times. It shows the volume of data pages that is moved between a hard disk drive and the main storage.
  • The Cross-Invalidation Activity block shows the number of buffer refresh activities caused by cross-invalidation.

    Cross-invalidation is necessary to maintain coherency of data within a Db2 data sharing group. It happens when a group member updates a data page and writes that page to the group buffer pool. All members that have this data page cached in their buffer pools are notified that the page was invalidated.

    A high level of cross-invalidation affects performance because it effectively reduces the amount of buffer pool space available to the system. When an invalidated page is required, it must be refreshed in the buffer pool, either by retrieving the page from the group buffer pool or from a hard disk drive.

  • The EDM Pool block shows the number of loads from a hard disk drive for cursor table (CT), package table (PT), and database directory (DBD) requests. For each event it shows the average size and load time.