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4.14.11 Suggestions for Business Monitor
This section describes ways to tune and maximize the performance of Business Monitor V8.0.
Improving concurrency by setting registry variables
DB2 allows you to defer row locks for cursor stability (CS) or read stability (RS) isolation
scans in certain cases. This deferral can last until a record is known to satisfy the predicates
of a query when row locking is performed during a table or index scan.
To improve concurrency, deferring row locking until after determining that a row qualifies for a
query might be possible. Usually, concurrency is improved by setting the registry variables
DB2_SKIPDELETED to permit scans to unconditionally skip uncommitted deletes, and
DB2_SKIPINSERTED to permit scans to unconditionally skip uncommitted inserts.
Example 4-4 shows how to enable these two registry variables for the MONITOR database.
Example 4-4 Enabling registry values DB2_SKIPDELETED and DB2_SKIPINSERTED
db2 connect to MONITOR
db2set DB2_SKIPDELETED=ON
db2set DB2_SKIPINSERTED=ON
Avoiding full transaction log
DB2 Health Monitor (HMON) regularly captures information about the database manager,
database, table spaces, and tables. It calculates health indicators based on data retrieved
from database system monitor elements, the operating system, and the DB2 system.
Transactions hang if HMON examines the status for the following table and the transaction
occupies the entire transaction log, resulting in an error with SQLCODE 964:
.SIBOWNER
To prevent this error, you can disable the HMON process by using the following command:
db2 update dbm cfg using HEALTH_MON OFF
Setting lock timeout properly
The LOCKTIMEOUT parameter specifies the number of seconds that an application waits to
obtain a lock. This parameter helps avoid global deadlocks for applications. If you set this
parameter to 0 (zero), the application does not wait for locks. In this situation, if the lock is
unavailable at the time of the request, the application immediately receives a -911 return
code.
If you set this parameter to -1, lock timeout detection is turned off.
A value of 30 seconds might be a good starting value; tune as necessary after setting this
value. The following example shows how to set this parameter for the MONITOR database.
Example 4-5 Starting value for LOCKTIMEOUT
db2 -v update db cfg for MONITOR using LOCKTIMEOUT 30
Limiting event XML to 32 KB where possible
Events that are small enough are persisted to a regular VARCHAR column in the incoming
events table; large events are persisted to a binary large object (BLOB) column instead. In
DB2, the largest VARCHAR column is 32768 bytes. Performance improves considerably
when a VARCHAR column is used instead of a BLOB.
Chapter 4. Performance tuning and configuration 87