DB2 z/OS Bufferpool display question

bill larsen

DB2 z/OS Bufferpool display question

Dear colleagues,

I can't have some problem to understand the  display (from command DIS BP DETAIL(INTERVAL)  of this production bufferpool - The interval length is only a few seconds.

DSNB411I  +DBX1 RANDOM GETPAGE    =446808,
            SYNC READ I/O (R) =25188,
            SEQ.   GETPAGE    =0,
            SYNC READ I/O (S) =0,
            DMTH HIT          =0,
            PAGE-INS REQUIRED =0,
            SEQUENTIAL        =86477,
            VPSEQT HIT        =0,
            RECLASSIFY        =132693,
DSNB412I  +DBX1 SEQUENTIAL PREFETCH -
             REQUESTS        =77,
             PREFETCH I/O    =13,
             PAGES READ      =13,
DSNB413I  +DBX1 LIST PREFETCH -,
             REQUESTS        =3,
             PREFETCH I/O    =3,
             PAGES READ      =16,
DSNB414I  +DBX1 DYNAMIC PREFETCH -,
             REQUESTS        =5299,
             PREFETCH I/O    =888,
             PAGES READ      =24082,
DSNB415I  +DBX1 PREFETCH DISABLED -,
             NO BUFFER       =0,
             NO READ ENGINE  =0,

Here are my questions :

1 - Why Sequential Getpage is Zero when Prefetch counters are far from 0 , and number of pages on the sequential LRU chain is >> 0

2 - There is 13 Sequential Prefetch IO  for (only) 13 pages read, i repeated the display, and i always get Number of IO = Number of Pages Read  - I imagine that this is not very optimized , but don't know in which situation this can occur....

The allocation is  VPSIZE 400000 , VPSEQT 60,

 

 

Thank you for your inputs

Regards

Bill Lars.

 

 

 

 

 

Venkat Srinivasan

RE: DB2 z/OS Bufferpool display question
(in response to bill larsen)

Normal with detail(interval) when the interval is too short. All of the counters can be zero. SLRU seems to show cumulative count. Compare the numbers with dis bufferpool detail(*) which shows accumulated counters since allocation. With seq prefetch, there is a wait for the first miss before triggering the prefetch engine. use statistics trace which provides counters at 1 minute interval.

Venkat

In Reply to bill larsen:

Dear colleagues,

I can't have some problem to understand the  display (from command DIS BP DETAIL(INTERVAL)  of this production bufferpool - The interval length is only a few seconds.

DSNB411I  +DBX1 RANDOM GETPAGE    =446808,
            SYNC READ I/O (R) =25188,
            SEQ.   GETPAGE    =0,
            SYNC READ I/O (S) =0,
            DMTH HIT          =0,
            PAGE-INS REQUIRED =0,
            SEQUENTIAL        =86477,
            VPSEQT HIT        =0,
            RECLASSIFY        =132693,
DSNB412I  +DBX1 SEQUENTIAL PREFETCH -
             REQUESTS        =77,
             PREFETCH I/O    =13,
             PAGES READ      =13,
DSNB413I  +DBX1 LIST PREFETCH -,
             REQUESTS        =3,
             PREFETCH I/O    =3,
             PAGES READ      =16,
DSNB414I  +DBX1 DYNAMIC PREFETCH -,
             REQUESTS        =5299,
             PREFETCH I/O    =888,
             PAGES READ      =24082,
DSNB415I  +DBX1 PREFETCH DISABLED -,
             NO BUFFER       =0,
             NO READ ENGINE  =0,

Here are my questions :

1 - Why Sequential Getpage is Zero when Prefetch counters are far from 0 , and number of pages on the sequential LRU chain is >> 0

2 - There is 13 Sequential Prefetch IO  for (only) 13 pages read, i repeated the display, and i always get Number of IO = Number of Pages Read  - I imagine that this is not very optimized , but don't know in which situation this can occur....

The allocation is  VPSIZE 400000 , VPSEQT 60,

 

 

Thank you for your inputs

Regards

Bill Lars.