DSNB775I PREFETCH READS DATA NOT RETURNED = r5

Explanation

This message is a section of output from the DISPLAY GROUP BUFFERPOOL command, which is part of message DSNB750I.

DSNB775I and DSNB789I: Prefetch read statistics

If the DISPLAY GROUPBUFFERPOOL command included the MDETAIL option, the output includes prefetch read statistics. 

DSNB775I -   PREFETCH READS
               DATA NOT RETURNED                       = r5 
DSNB789I -    REGISTER PAGE LIST                       = r7
               PAGES RETRIEVED                         = r8
r5
The number of pages that were retrieved from DASD, instead of the group buffer pool, in response to the register page list (RPL) request.

The RPL feedback indicated that the page was not cached in the group buffer pool. Therefore, to avoid a coupling facility read request for the page, Db2 retrieved the page directly from DASD. No coupling facility interactions are associated with this r5 value.

r7
The number of coupling facility requests to register interest in a list of pages. Db2 makes this request when sequential or list prefetch is used and the following conditions are met:
  • The Db2 member is running on a particular service level of MVS 5.2 or later.
  • The group buffer pool is allocated in a coupling facility with CFLEVEL=2 or higher.
r8
The number of coupling facility requests to prefetch a page in the group buffer pool as a result of feedback from the request to register a list of pages.