Setting MEMLIMIT

MEMLIMIT specifies the maximum amount of 64–bit storage that can be allocated to a single address space. Db2 Query Monitor uses 64–bit storage for two purposes. First, in an ISPF session, Db2 Query Monitor allocates a 1 megabyte log area. Second, when CAE Browser Client users specify the TopN function, 64–bit storage is allocated in the CAE Agent address space for the sorting operation associated with TopN.

For the log function in Db2 Query Monitor's ISPF user interface, a MEMLIMIT of 1 megabyte or greater is required.

For the CAE Browser Client and the TopN function, the amount of storage required to complete this processing is related to the number of UNIQUE SQL STATEMENTS that occur in the interval range that has been selected by the user. 64-bit storage is allocated in 1 megabyte chunks. Db2 Query Monitor will not allocate more than 4 gigabytes of 64-bit storage for the TopN function in the CAE Agent address space.

Approximately 700 unique SQL statements can be represented in 1 megabyte of 64–bit storage for the TopN function.

To estimate the MEMLIMIT setting for “Top N”, the customer can take the maximum number of UNIQUE SQL STATEMENTS that will be included within the interval range selected for “Top N” processing and divide by 700 to get a MEMLIMIT value. If the MEMLIMIT value is set too low, an ABEND 3193 will be generated in the CAE Agent address space. If ABEND 3193 occurs, the following message will be issued in the CAE Browser Client:

com.rocketsoft.nm.qm.ipc.AbendException: 
Abend U3193 during query for data source 16 (SQL METRICS STANDALONE);
access type 64 (:REDUCE BY KEYS THEN RETURN);

MEMLIMIT is specified in the SMFPRMxx parameter file in the System Parmlib. The default value is NOLIMIT, but if a value of less than 1M is specified, CQM260E will be issued and Query Monitor will not initialize under ISPF.10000M is therefore the minimum recommended MEMLIMIT setting.