Monitoring database buffers
One of the key resources in an online system is the database buffer pool. The efficiency of DL/I call service depends on the presence of the required database logical record in the buffer, so that segment retrieval does not require additional I/O.
This is especially true for HOLD calls with intervening database calls prior to a replace call.
Use the QUERY POOL command to view usage statistics for Fast Path buffer pools.
You can assess the general efficiency of the full-function pool management using the Database Buffer Pool report shown in the following example. The event counts on this report are not specific to a particular database or program but represent the pressure for use of the database pool.
Related reading: Refer to Database-Buffer-Pool report for more information on the Database Buffer Pool reports.
D A T A B A S E B U F F E R P O O L
FIX PREFIX/BUFFERS Y/Y
SUBPOOL ID 004K
SUBPOOL BUFFER SIZE 4096
TOTAL BUFFERS IN SUBPOOL 1000
16:09:59 16:25:10
START TRACE END TRACE DIFFERENCE
NUMBER OF LOCATE-TYPE CALLS 407636 4296793 3889157
NUMBER OF REQUESTS TO CREATE NEW BLOCKS 1 7 6
NUMBER OF BUFFER ALTER CALLS 75006 819359 744353
NUMBER OF PURGE CALLS 9137 93881 84744
NUMBER OF LOCATE-TYPE CALLS, DATA ALREADY IN OSAM POOL 313896 3317264 3003368
NUMBER OF BUFFERS SEARCHED BY ALL LOCATE-TYPE CALLS 453364 4779327 4325963
NUMBER OF READ I/O REQUESTS 86881 904487 817606
NUMBER OF SINGLE BLOCK WRITES BY BUFFER STEAL ROUTINE 0 0 0
NUMBER OF BLOCKS WRITTEN BY PURGE 32629 360434 327805
NUMBER OF LOCATE CALLS WAITED DUE TO BUSY ID 281 3173 2892
NUMBER OF LOCATE CALLS WAITED DUE TO BUFFER BUSY WRT 6 180 174
NUMBER OF LOCATE CALLS WAITED DUE TO BUFFER BUSY READ 0 0 0
NUMBER OF BUFFER STEAL/PURGE WAITED FOR OWNERSHIP RLSE 43 483 440
NUMBER OF BUFFER STEAL REQUESTS WAITED FOR BUFFERS 0 0 0
TOTAL NUMBER OF I/O ERRORS FOR THIS SUBPOOL 0 0 0
NUMBER OF BUFFERS LOCKED DUE TO WRITE ERRORS 0 0 0
QUOTIENT : TOTAL NUMBER OF OSAM READS + OSAM WRITES = 7.02
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TOTAL NUMBER OF TRANSACTIONSIf any of your databases use VSAM as access method, the IMS Monitor produces a series of reports headed VSAM BUFFER POOL, one for each subpool. The following example shows one of these reports.
***I M S M O N I T O R*** BUFFER POOL STATISTICS
V S A M B U F F E R P O O L
FIX INDEX/BLOCK/DATA N/Y/N
SHARED RESOURCE POOL ID VPL1
SHARED RESOURCE POOL TYPE D
SUBPOOL ID 2
SUBPOOL BUFFER SIZE 4096
NUMBER HIPERSPACE BUFFERS 0
TOTAL BUFFERS IN SUBPOOL 4
16:09:59 16:25:10
START TRACE END TRACE DIFFERENCE
NUMBER OF RETRIEVE BY RBA CALLS RECEIVED BY BUF HNDLR 432 6029 5597
NUMBER OF RETRIEVE BY KEY CALLS 40857 443840 402983
NUMBER OF LOGICAL RECORDS INSERTED INTO ESDS 414 6011 5597
NUMBER OF LOGICAL RECORDS INSERTED INTO KSDS 2132 25266 23134
NUMBER OF LOGICAL RECORDS ALTERED IN THIS SUBPOOL 0 0 0
NUMBER OF TIMES BACKGROUND WRITE FUNCTION INVOKED 0 0 0
NUMBER OF SYNCHRONIZATION CALLS RECEIVED 6494 70963 64469
NUMBER OF WRITE ERROR BUFFERS CURRENTLY IN THE SUBPOOL 0 0 0
LARGEST NUMBER OF WRITE ERRORS IN THE SUBPOOL 0 0 0
NUMBER OF VSAM GET CALLS ISSUED 44249 487181 442932
NUMBER OF VSAM SCHBFR CALLS ISSUED 0 0 0
NUMBER OF TIMES CTRL INTERVAL REQUESTED ALREADY IN POOL 11886 129668 117782
NUMBER OF CRTL INTERVALS READ FROM EXTERNAL STORAGE 32842 363635 330793
NUMBER OF VSAM WRITES INITIATED BY IMS 2370 29208 26838
NUMBER OF VSAM WRITES TO MAKE SPACE IN THE POOL 0 0 0
NUMBER OF VSAM READS FROM HIPERSPACE BUFFERS 0 0 0
NUMBER OF VSAM WRITES FROM HIPERSPACE BUFFERS 0 0 0
NUMBER OF FAILED VSAM READS FROM HIPERSPACE BUFFERS 0 0 0
NUMBER OF FAILED VSAM WRITES FROM HIPERSPACE BUFFERS 0 0 0
QUOTIENT : TOTAL NUMBER OF VSAM READS + VSAM WRITES = 2.19
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TOTAL NUMBER OF TRANSACTIONS