CREATE EVENT MONITOR (locking) statement

Invocation

This statement can be embedded in an application program or issued interactively. It is an executable statement that can be dynamically prepared only if DYNAMICRULES run behavior is in effect for the package (SQLSTATE 42509).

Authorization

Syntax

formatted-event-table-info

target-table-options

Notes:

• ¹ Each table option can be specified a maximum of one time (SQLSTATE 42613).
• ² Clauses can be separated with a space or a comma.

Description

event-monitor-name

Name of the event monitor. This is a one-part name. It is an SQL identifier (either ordinary or delimited). The event-monitor-name must not identify an event monitor that already exists in the catalog (SQLSTATE 42710).

FOR

Introduces the type of event to record.

LOCKING

Specifies that this passive event monitor will record any lock event produced when the database manager encounters one or more of these conditions:

• LOCKTIMEOUT: the lock has timed-out.
• DEADLOCK: the lock was involved in a deadlock (victim and participant(s)).
• LOCKWAIT: locks that are not acquired in the specified duration.

The creation of the lock event monitor does not indicate that the locking data will be collected immediately. The actual locking event of interest is controlled at the workload level or database level.

WRITE TO

Specifies the target for the data.

TABLE

Indicates that the target for the event monitor data is a set of formatted event tables. The event monitor separates the data stream into one or more logical data groups and inserts each group into a separate table. Data for groups having a target table is kept, whereas data for groups not having a target table is discarded. Each monitor element contained within a group is mapped to a table column with the same name. Only elements that have a corresponding table column are inserted into the table. Other elements are discarded.

formatted-event-table-info

Defines the target formatted event tables for the event monitor. This clause should specify each grouping that is to be recorded. However, if no evm-group clauses are specified, all groups for the event monitor type are recorded.

For more information about logical data groups, see Logical data groups and event monitor output tables .

evm-group

Identifies a logical data group for which a target table is being defined. The value depends upon the type of event monitor, as shown in the following table:

Type of Event Monitor	evm-group Value
Locking	LOCK LOCK_PARTICIPANTS LOCK_PARTICIPANT_ACTIVITIES LOCK_ACTIVITY_VALUES CONTROL

UNFORMATTED EVENT TABLE

Specifies that the target for the event monitor is an unformatted event table. The unformatted event table is used to store collected locking event monitor data. Data is stored in an internal binary format within an inlined BLOB column. Each event can insert multiple records into this table and each inserted record can be of a different type with the associated BLOB content varying as well. The data in the BLOB column is not in a readable format and requires conversion, through use of the db2evmonfmt Java-based tool, EVMON_FORMAT_UE_TO_XML table function, or EVMON_FORMAT_UE_TO_TABLES procedure, into a consumable format such as an XML document or a relational table.

target-table-options

Identifies options for the target table. If a value for target-table-options is not specified, CREATE EVENT MONITOR FOR LOCKING processing proceeds as follows:

• A derived table name is used (as explained in the description for TABLE table-name).
• A default table space is chosen using the same process as when a table is created without a table space name using CREATE TABLE.
• PCTDEACTIVATE is set to 100.

TABLE table-name

Specifies the name of the target table. The target table must be a non-partitioned table. If the name is unqualified, the table schema defaults to the value in the CURRENT SCHEMA special register. If a name is not provided for an unformatted event table, the unqualified name is equal to the event-monitor-name, that is, the unformatted event table will be named after the event monitor. If no name is provided for a formatted event table, the unqualified name is derived from evm-group and event-monitorname as follows:

   substring(evm-group CONCAT '_'
     CONCAT event-monitor-name,1,128)

IN tablespace-name

Defines the table space in which the table is to be created. The CREATE EVENT MONITOR FOR LOCKING statement does not create table spaces.

If a table space name is not provided, the table space is chosen using the same process as when a table is created without a table space name using CREATE TABLE.

When specifying the table space name for a formatted event table, the table space's page size affects the INLINE LOB lengths used Consider specifying a table space with as large a page size as possible in order to improve the INSERT performance of the event monitor.

PCTDEACTIVATE integer

If a table for the event monitor is being created in an automatic storage (non-temporary) or DMS table space, the PCTDEACTIVATE parameter specifies how full the table space must be before the event monitor automatically deactivates. The specified value, which represents a percentage, can range from 0 to 100. The default value is 100, where 100 means the event monitor deactivates when the table space becomes completely full. The default value assumed is 100 if PCTDEACTIVATE is not specified. This option is ignored for SMS table spaces.

Important: If the target table space has auto-resize enabled, set PCTDEACTIVATE to 100. Alternatively, omit this clause entirely to have the default of 100 apply. Otherwise, the event monitor might deactivate unexpectedly if the table space reaches the threshold specified by PCTDEACTIVTATE before the table space is automatically resized.

AUTOSTART

Specifies that the event monitor is to be automatically activated whenever the database partition on which the event monitor runs is activated. This is the default behavior of the locking event monitor.

MANUALSTART

Specifies that the event monitor must be activated manually using the SET EVENT MONITOR STATE statement. After a MANUALSTART event monitor has been activated, it can be deactivated only by using the SET EVENT MONITOR STATE statement or by stopping the instance.

Notes

• The target table is created when the CREATE EVENT MONITOR FOR LOCKING statement executes, if it doesn't already exist.
• During CREATE EVENT MONITOR FOR LOCKING processing, if a table is found to have already been defined for use by another event monitor, the CREATE EVENT MONITOR FOR LOCKING statement fails, and an error is passed back to the application program. A table is defined for use by another event monitor if the table name matches a value found in the SYSCAT.EVENTTABLES catalog view. If the table exists and is not defined for use by another event monitor, then the event monitor will re-use the table.
• Dropping the event monitor will not drop any tables. Any associated tables must be manually dropped after the event monitor is dropped.
• Lock event data is not automatically pruned from either unformatted event tables or regular tables created by this event monitor. An option for pruning data from UE tables is available when using the EVMON_FORMAT_UE_TO_TABLES procedure. For event monitors that write to regular tables, event data must be pruned manually.
• The FLUSH EVENT MONITOR statement is not applicable to this event monitor and will have no effect when issued against it.
• For unformatted event tables event data is inserted into the table into an inlined BLOB data column. Normally, BLOB data is stored in a separate LOB table space and can experience additional performance overhead as a result. When inlined into the data page of the base table, the BLOB data does not experience this overhead. The database manager will automatically inline the BLOB data portion of an unformatted event table record if the size of the BLOB data is less than the table space page size minus the record prefix. Therefore to achieve high efficiency and application throughput, it is suggested that you create the event monitor in as large a table space as possible up to and including a 32KB table space and associated bufferpool.

  Example

  The lock event monitor currently has the following two record types:

  • Application Info Record
  • Application Activity Record

  Application Info Record = maximum size 3.5KB

  Application Activity Record = 3KB + SQL statement text size (where SQL statement text size is max 2MB)

  The Application Info Record is very small and should always be inlined as long as a 4KB page size is being used. The Application Activity Record will be inlined based on the following formula:

  Application Activity Record < inline length (Pagesize - overhead non-LOB columns (0.5KB))
     3KB + SQL statement text < inline length (Pagesize - overhead non-LOB columns (0.5KB))
  
           SQL statement text < Pagesize - nonLOB overhead (1K) - 3KB
           SQL statement text < 16KB - 1KB - 3KB
                              < 12KB

  Therefore, when using a 16KB pagesize, the lock event monitor records will only be inlined if the SQL statement being captured is less than 12KB in size.

• Create only one locking event monitor per database. Creating more than one locking event monitor uses additional processor cycles and storage, without providing any additional data.
  Important: For compatibility with older versions of the product, all databases are created with the DB2DETAILDEADLOCK event monitor enabled. The locking event monitor introduced in Db2® Version 9.7 is the preferred mechanism for collecting data related to locks; the DB2DETAILEDDEALOCK event monitor is deprecated and might be removed in a future release. When you create a locking event monitor, disable and drop the DB2DETAILEDDEADLOCK event monitor to prevent the collection of duplicate, unnecessary information.

  To remove the DB2DETAILDEADLOCK event monitor, issue the following SQL statements:

  SET EVENT MONITOR DB2DETAILDEADLOCK state 0
  DROP EVENT MONITOR DB2DETAILDEADLOCK 

• In a partitioned database environment, data is written only to target tables on the database partitions where their table spaces exist. If a table space for a target table does not exist on some database partition, data for that target table is ignored. This behavior allows users to choose a subset of database partitions for monitoring to be chosen, by creating a table space that exists only on certain database partitions.
• In a partitioned database environment, if some target tables do not reside on a database partition, but other target tables do reside on that same database partition, only the data for the target unformatted event tables that do reside on that database partition is recorded.

Examples

• Example 1: This example creates a locking event monitor LOCKEVMON that will collect locking events that occur on the database of creation.

     CREATE EVENT MONITOR LOCKEVMON
       FOR LOCKING
       WRITE TO TABLE 

  This event monitor writes its output to the following tables:

  • LOCK_LOCKEVMON
  • LOCK_PARTICIPANTS_LOCKEVMON
  • LOCK_PARTICIPANT_ACTIVITIES_LOCKEVMON
  • LOCK_ACTIVITY_VALUES_LOCKEVMON
  • CONTROL_LOCKEVMON
• Example 2: This example creates a locking event monitor LOCKEVMON that will collect locking events that occur on the database of creation and store it in the unformatted event table IMRAN.LOCKEVENTS.

     CREATE EVENT MONITOR LOCKEVMON
       FOR LOCKING
       WRITE TO UNFORMATTED EVENT TABLE (TABLE IMRAN.LOCKEVENTS)

• Example 3: This example creates a locking event monitor LOCKEVMON that will collect locking events that occur on the database of creation and store it in the unformatted event table IMRAN.LOCKEVENTS in table space APPSPACE. The event monitor will deactivate when the table space becomes 85% full.

     CREATE EVENT MONITOR LOCKEVMON
       FOR LOCKING
       WRITE TO UNFORMATTED EVENT TABLE 
          (TABLE IMRAN.LOCKEVENTS IN APPSPACE PCTDEACTIVATE 85)