Lock Detail - P-Lock Requests

This section shows the event specific data for P-Lock requests.

P-Lock requests include the following events:
  • Page set or partition P-Lock request or page set or partition P-Lock negotiation request

    These P-Locks track inter-DB2 interest on a linear page set (table space or index) or a partition of a partitioned page set.

    The cached state of the page set or partition P-Lock tells DB2® which data sharing protocols must be used to maintain inter-DB2 buffer coherency for the page set or partition. For example, a cached state of IS tells DB2 that whenever a page belonging to that page set or partition is read into the buffer pool, the page must be registered to the coupling facility for cross-invalidation purposes. If the cached state were SIX, the coupling facility page registration would not be necessary.

    Normally the P-Lock is held by DB2 in the cached state. The P-Lock state determines whether or not the page set or partition is GBP-dependent:
    • If the page set or partition P-Lock is held in S or X, then the page set or partition is not GBP-dependent.
    • Otherwise, the page set or partition is GBP-dependent.
  • Page P-Lock request or page P-Lock negotiation request

    These P-Locks preserve the inter-DB2 cached page (buffer) coherency when row level locking is used and the page set or partition is actively R/W shared between two or more DB2 systems. The most common cases of subpage concurrency are row-level locking.

Note: Page P-Locking can add a significant overhead to data sharing if inter-DB2 workloads are not properly balanced. Class 21 is added to monitor these events without having to use the costly Class 7. However, page P-Lock events are recorded in Class 7 as well. Therefore, if Class 7 and 21 are both active, two records are reported for the same event.

The format of the data for these events is shown in Format of Page Set or Partition P-Lock Requests and Format of Page P-Lock Requests.

Format of Page Set or Partition P-Lock Requests

The following example shows the format of the data for this event.

 REQUEST=xxxxxx    OBJECT=xxxxxxxxxxx
 MEMBER =xxxxxxxx  REQUESTED STATE =xxxxx
 OLD STATE=xxxxx   OLD CACHED STATE=xxxxx
 NEW STATE=xxxxx   NEW CACHED STATE=xxxxx
 aaaaaaaaaaaaaaaaaaaaaaaa

Format of Page P-Lock Requests

The following example shows the format of the data for this event.

 REQUEST=xxxxxx    OBJECT=xxxxxxxxxxxxxxx
 MEMBER =xxxxxxxx  REQUESTED STATE=xxxxx
 OLD STATE=xxxxx   NEW STATE=xxxxx
 aaaaaaaaaaaaaaaaaaaaaaaa

Field description

Here is a description of the field labels shown in the previous examples:
REQUEST
The IRLM request type, which can be one of the following:
  • LOCK
  • UNLOCK
  • CHANGE
  • EXIT
OBJECT
The DB2 object type, which can be one of the following:
  • TABLESPACE
  • INDEXSPACE
  • DATA PAGE
  • HEADER PAGE
  • INDEX PAGE
  • SPACE MAP PAGE
MEMBER
A DB2 member name that depends on the request type:
  • For exit requests, the name of the DB2 member in conflict with this member's currently held P-Lock state.
  • For lock, unlock, and change requests, for which P-Lock is rejected, the name of the DB2 member in conflict with this request.
REQUESTED STATE
The requested lock state. It only applies to lock, change, and exit requests.

For exit requests, this is the P-Lock state requested by the member causing the P-Lock exit of this member. If the request from the other member was not in conflict with the state of this member, this field shows NH.

The values for this field are shown in Table 1.

Table 1. Lock State
State Description
NH Not held
IS This DB2 has R/O interest on the page set or partition and one or more other DB2s in the group have R/W interest
IX This DB2 has R/W interest on the page set or partition, one or more other DB2s in the group have R/O interest, and one or more can also have R/O interest
S This DB2 has R/O interest on the page set or partition and no other DB2 in the group has R/W interest but one or more can have R/O interest
SIX This DB2 has R/W interest on the page set or partition and no other DB2 in the group has R/W interest but one or more can have R/O interest
NSU Nonshared update
X This DB2 has R/W interest on the page set or partition and no other DB2 in the group has any interest
RD Request denied
OLD STATE
The previously held P-Lock state.

The values for this field are shown in Table 1.

NEW STATE
The newly held P-Lock state.

The values for this field are shown in Table 1.

OLD CACHED STATE
The previous P-Lock cached state.

The values for this field are shown in Table 1.

NEW CACHED STATE
The new P-Lock cached state.

The values for this field are shown in Table 1.

aaaaaaaaaaaaaaaaaaaaaaaa
Stands for the P-Lock attributes, which can be one or more of the following:
  • UNCONDITIONAL or CONDITIONAL.
  • RESTART or NONRESTART. Such a request instructs IRLM to convert a retained lock held by the DB2 system into an active lock. If the requested lock is not retained, IRLM grants the request as normal.
  • MODIFY or NONMODIFY.