CFRWPCT parameter
Max nonswappable CFR waiters
Summary
- Default value
- 0
- Parameter type
- System
- Where set
- Set in CCAIN, not resettable, range 0-75 percent
- Related products
- All
- Introduced
- Model 204 V6.1 or earlier
Description
Specifies the percentage of servers (NSERVS) that can be occupied by non-swappable users waiting for exclusive access to a critical file resource (CFR). These file-level resources consist of DIRECT, EXISTS, INDEX, and RECENQ.
When you issue a VIEW CFRWPCT command, the value returned is the actual number of servers (CFRWPCT * NSERVS), not the percentage of, that might contain users in a non-swappable wait for CFR in EXCL mode.
Performance tuning access to critical file resources
The CFRWPCT parameter helps balance access to CFRs at a site. A CFR is acquired in SHR mode for read access and EXCL mode for update access.
When many users have a CFR in SHR mode, users needing EXCL mode must wait and that wait is, by default, swappable. The result can be poor response time and increased system overhead due to server thrashing-users swapped in attempting to get a CFR in EXCL mode, then swapped out because the resource is unavailable, and repeating the cycle. To avoid this, CFRWPCT can be set to allow up to 75 percent of NSERVS to hold users waiting in a non-swappable wait for a CFR in EXCL mode.