Data sharing (BACCTDR)

GLOBAL CONT RATE(%)

Percentage of global lock contentions

This value is calculated as Global Suspends/total Global Locks x 100.0

Global Suspends is the total number of global lock contentions (QTGAIGLO + QTGASGLO + QTGAFLSE).

Total Global Locks is the sum of:

• Lock requests (QTGALSLM)
• Change requests (QTGACSLM)
• Unlock requests (QTGAUSLM)
• Global lock contentions (QTGAIGLO + QTGASGLO + QTGAFLSE)

FALSE CONT RATE(%)

Percentage of global lock false contentions

This value is calculated as False Contentions / Global Suspends x 100.0

False Contentions is the total number of global lock suspensions due to false contention (QTGAFLSE).

Global Suspends is the total number of global lock contentions (QTGAIGLO + QTGASGLO + QTGAFLSE).

L—LOCK XES RATE(%)

Number of lock requests propagated to z/OS XES (QTGALSLM)

LOCK REQ—PLOCKS

Number of lock requests for P-locks (QTGALPLK)

Physical locks (P-locks) are acquired in the DB2 data sharing environment at the data set level to allow DB2 to determine whether an object is of intersystem interest. Concurrency is still managed as before with transaction (or logical) locks (L-locks). A P-lock is acquired for the first transaction that accesses an object (table space, index space, partition) but it is owned by the subsystem. Page P-locks are used for row-level locking. P-locks never cause timeouts, as the lock mode can be negotiated. Intersystem interest occurs only when at least one DB2 has update interest and one or more others have read interest.

UNLOCK REQ—PLOCKS

Number of unlock requests for P-locks (QTGAUPLK)

This number represents the number of IRLM unlock requests in a data sharing environment.

CHANGE REQ—PLOCKS

Number of change requests for P-locks (QTGACPLK)

This counter is incremented when a P-lock has been established and the IRLM associated with this DB2 determines that the nature of a that lock must be changed for page sets which are of intersystem interest. The number of P-lock changes reflects the changing status of page sets as access modes change and as the lock state is negotiated between DB2s.

LOCK REQ—XES

Number of lock requests propagated to MVS XES synchronously (QTGALSLM)

This number is incremented for all data sharing locks when a request for a lock on an object of DB2 intersystem interest is sent to MVS Cross-System Services. Both L-locks and P-locks are included. The count is not incremented if a suspension occurs. This number reflects the global lock activity.

UNLOCK REQ—XES

Number of unlock requests propagated to MVS XES synchronously (QTGAUSLM)

This number is incremented for all data sharing locks when an unlock request for an object of DB2 intersystem interest is sent to MVS Cross-System Services. Both L-locks and P-locks are included. The count is not incremented if a suspension occurs. This number reflects the number of resources propagated for unlocks, not just the number of unlock requests, which may be generic for a group of resources.

CHANGE REQ—XES

Number of change requests propagated to MVS XES synchronously (QTGACSLM)

This number is incremented for all data sharing locks when a change request for a lock on an object of DB2 intersystem interest is sent to MVS Cross-System Services. Both L-locks and P-locks are included. The count is not incremented if a suspension occurs. This number reflects the number of change requests for locks of intersystem interest.

SUSPENDS—IRLM

Number of global IRLM suspensions (QTGAIGLO)

This number is incremented when an incompatible lock is requested on an object (page set, page or row) in a data sharing environment that is being held by another system. For a complete picture of global contention, all three global suspension counts must be considered. This counter is a measure of intersystem contention. All locks of intrasystem contention are resolved prior to the IRLM checking for intersystem contention. This number is the number of true waits for another thread on a different MVS that has an incompatible lock type to the requester. Global contention requires intersystem communication to resolve the conflict.

SUSPENDS—XES

Number of global XES suspensions (QTGASGLO)

This counter is a measure of MVS XES global resource contention. The MVS XES lock states were in conflict but IRLM lock states were not.

SUSPENDS—FALSE

Number of false global suspensions (QTGAFLSE)

This counter is incremented every time MVS Cross-System Services detects contention on the resource hash class but not on the resource itself.

Tuning Tip: MVS Cross-System Services uses a hash table for efficient determination of whether a resource is locked. This hash table points to a number of synonyms. When contention exists on the hash class but not on the actual object, this condition is false contention. The more resources declared to be of intersystem interest, the more chances there are of this condition occurring. The CF lock structure may be too small.

INCOMP LOCK

Number of global requests denied because of incompatible retained lock (QTGADRTA)

This number is incremented every time Global Lock Services denies a lock request because an incompatible lock type has been retained for the requested resources. This number reflects the instances in which intersystem access to a page or row cannot be obtained because another thread on another system had access to the resource requested but the other system failed. The Coupling Facility retains locks until the other system has come up to complete the unit of work.

NOTIFY SENT

Number of notify messages sent (QTGANTFY)

This number represents the number of messages passed to the coupling facility; for example, to notify other members that DBDs have been changed due to CREATE, ALTER, or DROP statements. This value is the outbound traffic to the coupling facility in a data sharing complex.

L—LOCK RATE(%)

Number of transaction locks (L-Locks) that were propagated to XES and the coupling facility, shown as a percentage of lock requests (QTGSLSLM/QTXALOCK)