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: For more information about the Database Buffer Pool reports, see Database-Buffer-Pool report.
If any of your databases use VSAM as the 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.
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
17:08:15 17:10:16
NUMBER OF LOCATE-TYPE CALLS 1117674 1676213 558539
NUMBER OF REQUESTS TO CREATE NEW BLOCKS 0 0 0
NUMBER OF BUFFER ALTER CALLS 215874 322936 107062
NUMBER OF PURGE CALLS 25077 37454 12377
NUMBER OF LOCATE-TYPE CALLS, DATA ALREADY IN OSAM POOL 870306 1301187 430881
NUMBER OF BUFFERS SEARCHED BY ALL LOCATE-TYPE CALLS 1258247 1886843 628596
NUMBER OF READ I/O REQUESTS 238165 360260 122095
NUMBER OF SINGLE BLOCK WRITES BY BUFFER STEAL ROUTINE 0 0 0
NUMBER OF BLOCKS WRITTEN BY PURGE 95057 142413 47356
NUMBER OF LOCATE CALLS WAITED DUE TO BUSY ID 780 1297 517
NUMBER OF LOCATE CALLS WAITED DUE TO BUFFER BUSY WRT 0 0 0
NUMBER OF LOCATE CALLS WAITED DUE TO BUFFER BUSY READ 0 0 0
NUMBER OF BUFFER STEAL/PURGE WAITED FOR OWNERSHIP RLSE 178 261 83
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 = 6.98
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TOTAL NUMBER OF TRANSACTIONSThe following example shows a sample of the VSAM-Buffer-Pool report.
***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 50
TOTAL BUFFERS IN SUBPOOL 1000
17:08:15 17:10:16
NUMBER OF RETRIEVE BY RBA CALLS RECEIVED BY BUF HNDLR 152 330 178
NUMBER OF RETRIEVE BY KEY CALLS 117780 178424 60644
NUMBER OF LOGICAL RECORDS INSERTED INTO ESDS 132 310 178
NUMBER OF LOGICAL RECORDS INSERTED INTO KSDS 6460 9853 3393
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 18566 27923 9357
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 124648 189220 64572
NUMBER OF VSAM SCHBFR CALLS ISSUED 0 0 0
NUMBER OF TIMES CTRL INTERVAL REQUESTED ALREADY IN POOL 33662 51088 17426
NUMBER OF CRTL INTERVALS READ FROM EXTERNAL STORAGE 91169 138505 47336
NUMBER OF VSAM WRITES INITIATED BY IMS 6022 9251 3229
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 50 50 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 = 2.08
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TOTAL NUMBER OF TRANSACTIONS