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DB2 Manager User Guide 51
StorageTek Proprietary
• Terminate the DB2 Manager control region.
All messages issued by DB2 Manager in response to an operator request are
documented in chapter 7 of this manual. This section specifies operator
request formats, and gives examples of DB2 Manager responses to these
requests.
Display summary status
D(ISPLAY)
This request is used to produce a summary display of the status of the DB2
Manager control region processing configuration.
The DISPLAY command may be abbreviated to the single character 'D'.
DB2 Manager creates a number of tape and disk reader tasks in the control
region to perform retrieval of objects from Archive Manager. Each tape reader
task is capable of processing one tape volume at any one time. The number
of tape reader tasks created is initially equal to the value of the MAXTRDR
parameter at DB2 Manager initialization. Increasing this value during DB2
Manager operation will cause a similar increase in the number of tape reader
tasks. DB2 Manager will only be able to process as many tape volumes
simultaneously as there are initialized tape reader tasks.
Disk reader tasks may process multiple Archive Manager disk (‘K’) copy
datasets in one invocation (ie. the task’s request queue may contain requests
for retrieval of objects from different disk datasets). DB2 Manager attempts
to balance the length of the request queues for the disk reader tasks.
Increasing the value of MAXDRDR will reduce the average length of the disk
reader task request queues. For most operational environments, the default
MAXDRDR value of 4 will be sufficient. Note that the MAXQLEN parameter is
not used to control a disk reader task request queue length; there is no limit
to the number of requests which may be queued for each disk reader task.
If no disk reader tasks are available (MAXDRDR=0), a retrieval request for a
disk-resident object will be passed to an DB2 Manager tape reader task, if
one is available. This task will issue a standard Archive Manager object
retrieval request, which will still be satisfied wherever possible by Archive
Manager from an object’s disk copy. Setting the value of MAXDRDR to 0 in
these circumstances is not recommended, as it may cause requests for
retrieval of disk-resident objects to be rejected because there are no free
tape reader tasks.
Writer tasks are capable of updating a single Archive Manager database at
any one time. In addition, an Archive Manager database will not be updated
by more than one writer task simultaneously. The number of writer tasks is
controlled via the MAXTWTR initialization parameter.
A summary status request will display the current values of the MAXTRDR,
MAXDRDR, MAXTWTR, MAXSCHED, MAXQLEN, RETAINTAPE,
TAPEWAIT, OBJSIZE, READTIMEOUT and WRITETIMEOUT parameters,