What to look for in a OMEGAMON statistics report

Explanation of fields

 A 

The number of requests made to read a page from the group buffer pool because the page was invalidated in the member's buffer pool. The member found the required page in the group buffer pool.

 B 

The number of requests to read a page from the group buffer pool that were required because the page was invalidated in the member's buffer pool. The member did not find the data in the group buffer pool and had to retrieve the page from DASD. If this number is high, use the following formula to calculate the percentage:  B  /( A  +  B ). If the result is greater than 10%, consider increasing the size of the group buffer pool.

 C 

The number of requests made to read a page from the group buffer pool because the page was not in the member's buffer pool. The member found the page in the group buffer pool.

 D 

The number of times Db2 unregistered interest for a single page. This happens when Db2 steals pages from the member's buffer pool that belong to GBP-dependent page sets or partitions.

 E 

The number of data pages that were cast out of the member's group buffer pool. Castout to a page set or partition is done by the castout owner of the page set or partition. This is normally the Db2 subsystem that had the first update intent on the page set or partition.

 F 

The number of times Db2 issued an unlock request to the coupling facility for completed castout I/Os. When pages are cast out to DASD, they are locked for castout in the coupling facility. This castout lock is not an IRLM lock; its function is to ensure that only one system can cast out a given page at a time.

 G 

The number of requests issued by the group buffer pool to determine which pages, from a particular page set or partition, must be cast out because they are cached as changed pages. This request is issued either by the page set or partition castout owner, or, when the group buffer pool castout threshold is reached by the group buffer pool structure owner.

 H 

The number of requests issued by the group buffer pool structure owner to read the directory entries of all changed pages in the group buffer pool. This request is issued at group buffer pool checkpoints to record the oldest recovery log record sequence number (LRSN). It is used as a basis for recovery if the group buffer pool fails. Such requests might have to be issued several times for each group buffer pool checkpoint to read the directory entries for all changed pages.

 I 

The number of times Db2 requested statistics information from the group buffer pool. It is issued by the group buffer pool structure owner at timed intervals to determine whether the group buffer pool castout threshold (GBPOOLT) has been reached.

 J 

The number of times Db2 registered interest in a single page. These are "register-only" requests, which means that Db2 is not requesting any data back from the request. This request is made only to create a directory entry for the page to be used for cross-invalidation when the page set or partition P-Lock is downgraded from S to IS mode, or from SIX to IX mode.

 K 

The number of requests made by Db2 to delete directory and data entries associated with a particular page set or partition from the group buffer pool. Db2 issues this request when it changes a page set or partition from GBP-dependent to non GBP-dependent. Db2 also issues this request for objects that are defined with GBPCACHE ALL when those objects are first opened.

 L 

The number of IXLCACHE invocations for the primary group buffer pool.

 M 

The number of times an explicit coupling facility cross-invalidation request was issued.

 N 

The number of times group buffer pool castout was initiated because the group buffer pool class castout threshold was detected.

 O 

The number of times a group buffer pool castout was initiated because the group buffer pool castout threshold was detected.

 P 

The number of group buffer pool checkpoints triggered by this member.

 Q 

The number of coupling facility write requests that could not complete due to a lack of coupling facility storage resources.A high number indicates a shortage of group buffer pool data elements because the size of the group buffer pool is too small, or because castout is not keeping up with the rate that changed pages are written. If the pages were not written to LPL, then the write retry attempt was successful.

 R 

The number of coupling facility requests to read the castout statistics for the secondary group buffer pool. These requests are issued by the group buffer pool structure owner to check for orphaned data entries in the secondary group buffer pool.

 S 

The number of changed pages written synchronously to the group buffer pool. Pages are written with Write and Register (WAR) requests or Write and Register Multiple (WARM) requests. At commit time changed pages are forced from the member's virtual buffer pool to the coupling facility.

 T 

The number of changed pages written asynchronously to the group buffer pool. Pages are written in response to Write and Register (WAR) and Write and Register Multiple (WARM) requests. Changed pages can be written from the member's virtual buffer pool to the group coupling facility before the application commits. This happens when, for example, a local buffer pool threshold is reached, or when P-Lock negotiation forces the pages on the vertical deferred write queue to be written to the group buffer pool.

 U 

The number of P-lock negotiations between data sharing members for space map pages. If this number is high, identify the objects by using IFCID 0259 performance trace. If the high number is caused by insert-intensive applications, consider using the MEMBER CLUSTER or TRACKMOD NO options, or both.

 V 

The number of P-lock negotiations between data sharing members for data pages. If this number is high, identify the objects by using IFCID 0259 performance trace. The typical cause is tables spaces that use row-level locking. For small tables, consider using MAXROWS=1, and VDWQT=0 to free page P-locks as soon as possible.

 W 

The number of p-lock negotiations between members for index leaf pages. If this number is high, identify the objects by using IFCID 0259 performance trace. The typical cause is applications that do ascending or descending updates of index keys. Creating indexes with randomized keys might help this situation. However, doing so might incur other performance degradation because more get-page operations, I/O, and lock requests are needed.