Data Sharing Locking

This topic shows detailed information about Accounting - Data Sharing Locking.

This block shows the locking activity within a data sharing group.

For formatting reasons, OMEGAMON XE for DB2 PE shows different labels for report and trace. In the following example both layouts are shown, the report on the left, and the trace layout on the right.

Report:                                       Trace:

DATA SHARING          AVERAGE     TOTAL       DATA SHARING    TOTAL
-------------------  --------  --------       ------------ --------
GLOBAL CONT RATE(%)       N/C       N/A       GLOB CONT(%)    11.35
FALSE CONT RATE(%)        N/C       N/A       FALS CONT(%)     0.00
P/L-LOCKS XES(%)          N/C       N/A       P/L-LOCKS(%)       89
LOCK REQ   - PLOCKS      0.00         0       P-LOCK REQ        159
UNLOCK REQ - PLOCKS      0.00         0       P-UNLOCK REQ       45
CHANGE REQ - PLOCKS      0.00         0       P-CHANGE REQ       40
LOCK REQ   - XES         0.00         0       LOCK - XES        286
UNLOCK REQ - XES         0.00         0       UNLOCK-XES        103
CHANGE REQ - XES         0.00         0       CHANGE-XES         47
SUSPENDS   - IRLM        0.00         0       SUSP - IRLM        64
SUSPENDS   - XES         0.00         0       SUSP - XES          0
CONVERSIONS- XES         0.00         0       CONV - XES         64
FALSE CONTENTIONS        0.00         0       FALSE CONT          0
INCOMPATIBLE LOCKS       0.00         0       INCOMP.LOCK         0
NOTIFY MSGS SENT         0.00         0       NOTIFY SENT         3

GLOBAL CONT RATE(%) (GLOB CONT(%))

The total number of suspends because of contention divided by the total number of synchronous requests that went to XES, and the lock requests that were converted from synchronous to asynchronous locks, and the locks because of child lock propagation.

Field Name: AGLOBRAT

FALSE CONT RATE(%) (FALS CONT(%))

The total number of suspends because of false contention divided by the total number of synchronous requests that went to XES and the lock requests that were converted from synchronous to asynchronous locks.

A false contention is where two different locks on different resources hash to the same lock entry.

Field Name: AFLSERAT

P/L-LOCKS XES(%) (P/L-LOCKS (%))

Shows the percentage of P/L-lock requests that were propagated to XES synchronously.

Background and Tuning Information

This number reflects the effects of explicit hierarchical locking and other locking optimizations. In an environment where all the workload is data sharing, a value of 94% means that 6% of all transaction locks were not propagated to XES due to Data-Sharing locking optimizations.

DB2 has optimizations to reduce the need to go beyond the local IRLM whenever possible:

• Explicit hierarchical locking allows IRLM to grant child locks locally when there is no inter-DB2 R/W interest on the parent.
• If there is a single DB2 with update interest, and multiple DB2s with read-only interest, DB2 propagates fewer locks than when all DB2s have update interest in the page set.
• All locks that go beyond the local IRLM are owned by the subsystem, not the individual work unit. This allows for further optimization. Only the most restrictive lock mode for an object on a given subsystem must be propagated to XES and the coupling facility. A new lock that is equally, or less, restrictive than the currently held lock is not propagated.

Field Name: ALLOCRAT

LOCK REQ - PLOCKS (P-LOCK REQ)

The number of lock requests for P-locks.

Field Name: QTGALPLK

UNLOCK REQ - PLOCKS (P-UNLOCK REQ)

The number of unlock requests for P-locks.

Field Name: QTGAUPLK

CHANGE REQ - PLOCKS (P-CHANGE REQ)

The number of change requests for P-locks.

Field Name: QTGACPLK

LOCK REQ - XES (LOCK - XES)

The number of P/L-lock requests propagated to z/OS XES synchronously.

This number is not incremented if the request is suspended before going to XES.

Field Name: QTGALSLM

UNLOCK REQ - XES (UNLOCK-XES)

The number of unlock requests propagated to z/OS XES.

Field Name: QTGAUSLM

CHANGE REQ - XES (CHANGE-XES)

The number of change requests propagated to z/OS XES.

Field Name: QTGACSLM

SUSPENDS - IRLM (SUSP - IRLM)

The number of suspensions due to IRLM global resource contention (IRLM lock states were in conflict).

Field Name: QTGAIGLO

SUSPENDS - XES (SUSP - XES)

The number of suspensions due to z/OS XES global resource contention (z/OS XES lock states were in conflict whereas IRLM lock states were not).

Field Name: QTGASGLO

SUSPENDS - CONV (SUSP - CONV)

The total number of sync-to-async heuristic conversions for LOCK requests in XES. This conversion is done when XES determines that it is more efficient to drive the request asynchronously to the coupling facility (CF).

Field Name: QTGAFLSE

FALSE CONTENTIONS

The total number of false contentions for LOCK and UNLOCK requests. A false contention occurs when different resource names hash to the same entry in the coupling facility (CF) lock table. The CF detects contention within the hash entry, and XES uses intersystem messaging to determine that no actual resource contention exists.

Field Name: QTGAFCNT

INCOMPATIBLE LOCKS (INCOMP.LOCK)

The number of global lock or change requests denied or suspended due to an incompatible retained lock.

Field Name: QTGADRTA

NOTIFY MSGS SENT (NOTIFY SENT)

The number of notify messages sent.

Field Name: QTGANTFY