DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

For partitioned table spaces defined with LOCKPART NO, prior versions of DB2 lock only the
last partition to indicate we have a lock on the whole table space. There are no L-locks held
on each of the partition page sets. So, when should we propagate the child L-locks for the
various partitions that are being used? We cannot tell by looking at the table space parent
L-locks that we need to propagate the child locks since there no longer is a lock contention
conflict that can trigger child lock propagation, and we cannot determine how each partition
page set is being used by looking at the page set P-locks that are held at the partition level,
while the parent L-lock is at the table space level with LOCKPART NO.
To overcome this problem, DB2 V8 obtains locks at the part level. LOCKPART NO behaves
the same as LOCKPART YES.
In addition, LOCKPART YES is not compatible with LOCKSIZE TABLESPACE. However, if
LOCKPART NO and LOCKSIZE TABLESPACE are specified then we will lock every partition,
just as every partition is locked today when LOCKPART YES is used with
ACQUIRE(ALLOCATE). With this change you may see additional locks being acquired on
individual partitions even though LOCKPART(NO) is specified.
This change to the LOCKPART parameter behavior applies to both data sharing and non-data
sharing environments.
Since the new locking protocol cannot co-exist with the old, the new protocol will only take
effect after the first group-wide shutdown and restart after the data sharing group is in
new-function mode (NFM). You do not have to delete the lock structure from the coupling
facility prior to restarting DB2, to trigger DB2 on group restart to build a new lock structure. In
addition, Protocol Level 2 will not be enabled if you merely ask DB2 to rebuild the lock
structure while any DB2 member remains active.
The new mapping takes effect after the restart of the first member, after successful quiesce of
all members in the DB2 data sharing group. So, to enable this feature, a group-wide outage is
required.
No other changes are required to take advantage of this enhancement.
You can use the -DISPLAY GROUP command to check whether the new locking protocol is
used (mapping IX IRLM L-locks to an S XES lock). Example 8-1 shows the output from a
-DISPLAY GROUP command which shows Protocol Level 2 is active.
Example 8-1 Sample -DISPLAY GROUP output
DSN7100I -DT21 DSN7GCMD
*** BEGIN DISPLAY OF GROUP(DSNT2 ) GROUP LEVEL(810) MODE(N)
PROTOCOL LEVEL(2) GROUP ATTACH NAME(DT2G)
--------------------------------------------------------------------
DB2 DB2 SYSTEM IRLM
MEMBER ID SUBSYS CMDPREF STATUS LVL NAME SUBSYS IRLMPROC
-------- --- ---- -------- -------- --- -------- ---- --------
DT21 1 DT21 -DT21 ACTIVE 810 STLABB9 IT21 DT21IRLM
DT22 3 DT22 -DT22 FAILED 810 STLABB6 IT22 DT22IRLM
The use of locking Protocol Level 2 requires that the PTFs for the following APARs are
applied: PQ87756, PQ87168, and PQ86904 (IRLM).
Chapter 8. Data sharing enhancements 327