Analyze the file system latch contention

The FILE SYSTEM LATCH ACTIVITY table shows what user or product is holding the file system latch and what users are waiting for the latch. For example, refer to Figure 1.
Figure 1. Example: FILE SYSTEM LATCH ACTIVITY table
FILE SYSTEM LATCH ACTIVITY:            
    USER   ASID     TCB            SHR/EXCL                     AGE   
----------------------------------------------------------------------
Latch 432 FILE SYSTEM:  THE.FILESYS.NAME
 HOLDER(S):                  
   User10  0044  00880460            SHR                     00:12:08
        IS DOING: NFS ReadCall              
        FILE: somefilename                 (88,1234)
   User11  0045  00880460            SHR                     00:15:58
        IS DOING: NFS ReadCall              
        FILE: somefilename                 (88,1234)
    WAITER(S):                                                          
   OMVS    000E  008E9B58            EXCL                    00.01.10
Latch 678 FILE SYSTEM:  ANOTHER.FILESYS.NAME
 HOLDER(S):                  
   OMVS    000E  00820420            EXCL                    00:12:08
     IS DOING: ZFS SyncCall / Osi_Wait
    WAITER(S):                                                           
   User12  0022  008D97C8            SHR                     00.00.05
   User15  0072  008E9B58            SHR                     00.01.10
The key to resolving file system latch contention is in the HOLDER: and IS DOING: fields highlighted in Figure 1.
  • The HOLDER: field tells you what program is holding the file system latch.
  • The IS DOING: field tells you where, in what element or product, the program holding the file system latch is running, and what the program is doing. First, we'll decode field IS DOING. IS DOING is displayed as IS DOING: activity / [pfs_qualifier]:
    activity
    Description of what the holding task is doing. activity is displayed as either:
    • A wait, such as a file system latch wait, indicating that the latch holder is waiting for another latch.
    • The type of physical file system (PFS) and the operation that the task was called to do, such as READ, WRITE, MOUNT, or FSYNCH
    pfs_qualifier
    If the activity field shows a PFS, the pfs_qualifier field shows what the PFS is doing. For example, pfs_qualifier might show:
Parent topic: Procedure: Diagnosing and resolving latch contention