The CF Cache Structure Statistics section
This report section shows coupling facility cache structure statistics, which are retrieved from IFCID 254.
The statistics break out the major activity details of the cache structure. A cache structure is a storage area that is used as group buffer pool for a DB2® data sharing group.
OMEGAMON XE FOR DB2 PE (V5R4M0) - BUFFER POOL ACTIVITY REPORT PAGE: 1-90
ORDER: BPID-QPAGESET
SORTBY: BPID,ASYNCPAGE TOP: 17 LEVEL: SUMMARY
GROUP: DBE1 LOCATION: PMODBE1 DB2 VERSION: V11
MEMBER: SE11 REQUESTED FROM: NOT SPECIFIED TO: NOT SPECIFIED
SUBSYSTEM: SE11 INTERVAL FROM: 12/04/15 13:32:25 TO: 12/04/15 13:44:27
======= CF Cache Structure Statistics =======
Group Buffer Pool GBP0 GBP32K GBP8K0
------------------------- ---------- ---------- ----------
Explicit XI counter 0 0 0
Read Hit 3290 0 0
Read miss directory Hit 7298 0 0
Read miss assign.suppres. 3224 604 676
Read miss name assigned 37514 117 161
Read miss cache full 0 0 0
Changed page write Hit 105145 117 1872
Clean page write Hit 0 0 0
Write miss cache full 0 0 0
Total changed 1 0 0
Directory entry 349 0 14
Data entry 1 0 10
Directory entry reclaim 0 221 0
Date entry reclaim 54540 0 193
XI dir. entry reclaim 0 208 0
Castout 59185 117 512
Secondary-GBP
Directory entry 0 0 0
Data entry 0 0 0
Changed page write Hit 0 0 0
Total changed 0 0 0
Write miss cache full 0 0 0
========================= ========== ========== ==========
- Explicit XI counter
- The number of times a request was made to the group coupling facility to explicitly cross-invalidate a page and a number of XI signals were sent because the page was cached in one or more Db2 buffer pools. Derived from the Db2 field QW0254CI.
- Read hit
- The number of coupling facility read requests in which data was returned. Derived from the Db2 field QW0254RH.
- Read miss directory hit
- The number of coupling facility read requests for a page in which data was not returned but the page name was already assigned in the coupling facility directory (SES did not have to assign a directory entry for the page). Derived from the Db2 field QW0254RD.
- Read miss assign. suppres.
- The number of times that a coupling facility read request specified a page for which no directory entry exists and no directory entry is created. Db2 does not create a directory entry if it does not need to register the page to the coupling facility for cross-invalidation (XI); that is when no other Db2 member in the group has R/W interest in the page set/partition. Derived from the Db2 field QW0254RS.
- Read miss name assigned
- The number of times that a coupling facility read request specified a page for which a directory entry was created. Derived from the Db2 field QW0254RN.
- Read miss cache full
- The number of times that a coupling facility read request specified a page for which no directory entry exists and no directory entry is created due to the lack of storage in the group buffer pool. A nonzero value in this field indicates that the backing coupling facility cache structure size might be too small to support the current workload. Derived from the Db2 field QW0254RF.
- Clean page write hit
- The number of facility write requests for clean pages successfully completed. Derived from the Db2 field QW0254WC.
- Changed page write hit
- The number of coupling facility write requests for changed pages that have successfully completed. Derived from the Db2 field QW0254WH.
- Write miss cache full
- The number of coupling facility write requests that could not
complete due to a lack of coupling facility storage resources. Derived
from the Db2 field QW0254WF.
Ideally, this value should be zero. These GBP write fails occur when a changed page must be written to the GBP and no GBP data entries are available. A data entry is unavailable if it contains a changed page that has not yet been externalized to a hard disk drive (casted out). A nonzero value indicates that castout processing cannot keep pace with the rate at which changed pages are being written to the group buffer pool. Usually, the best solution is to enlarge the GBP. Changing the castout threshold could lead to higher processor utilization for the mainframes handling castout processing.
- XI dir. entry reclaim
- The number of times that a directory entry was stolen and XI signals had to be sent because the page for the directory entry was cached in one or more Db2 buffer pools. Derived from the Db2 field QW0254XR.
- Directory entry reclaim
- The number of times that a page name assignment required a coupling
facility directory entry to be reclaimed (stolen). Derived from the Db2 field
QW0254DR.
Directory entry reclaims occur when a data or index page must be registered in the GPB but all the directory entries are in use. Then, an in-use entry will be reclaimed. When this happens, the copies of the page associated with the reclaimed directory entry are invalidated, even if they have not been changed. Invalidation causes extra reads from a hard disk drive, which can reduce system throughput. Consequently, larger group buffer pools reduce or eliminate directory entry reclaims because they can hold more entries. See also
Data entry reclaim
. - Data entry reclaim
- The number of times that a page name assignment required a coupling
facility data entry to be reclaimed (stolen). Derived from the Db2 field
QW0254TR.
See also
Directory entry reclaim
. Besides the size of the group buffer pool, reclaims are also influenced by the ratio between directory entries and data entries. Nonzero values do not necessarily indicate a performance bottleneck; however, they should be further investigated. - Total changed
- The snapshot value of the current number of changed pages. Derived from the Db2 field QW0254TC.
- Castout
- The number of castout operations performed. Derived from the Db2 field QW0254CC.
- Directory entry
- The number of allocated directory entries (not cumulative). Derived from the Db2 field QW0254DE.
- Data entry
- The number of allocated data entries (not cumulative). Derived from the Db2 field QW0254TE.
- Secondary-GBP — Directory entry
- The number of allocated directory entries. This is a snapshot value. Derived from the Db2 field QW02542D.
- Secondary-GBP — Data entry
- The number of allocated data entries. This is a snapshot value. Derived from the Db2 field QW02542T.
- Secondary-GBP — Changed page write hit
- The number of successful coupling facility write requests for changed pages. Derived from the Db2 field QW02542W.
- Secondary-GBP — Total changed
- The number of allocated data entries that are currently in
changed
state. This is a snapshot value. Derived from the Db2 field QW02542C. - Secondary-GBP — Write miss cache full
- The number of unsuccessful coupling facility write requests because of insufficient coupling facility storage resources. Derived from the Db2 field QW02542F.