{"id":240604,"date":"2022-05-04T02:15:00","date_gmt":"2022-05-04T09:15:00","guid":{"rendered":"https:\/\/virtual-dba.com\/?p=240604"},"modified":"2022-05-04T08:59:54","modified_gmt":"2022-05-04T15:59:54","slug":"investigating-locking-in-db2","status":"publish","type":"post","link":"https:\/\/virtual-dba.com\/blog\/investigating-locking-in-db2\/","title":{"rendered":"Investigating Locking in Db2"},"content":{"rendered":"\n

The purpose of this article is to provide guidance on the various ways available for getting basic information about locking events in a Db2 database. Where possible the information gathered allows for targeting a specific table. The information provided by these methods is only for starting investigations into locking issues. Links are provided after each method for additional information.<\/p>\n\n\n\n

Conventions<\/h2>\n\n\n\n

Text in statements that are wrapped in brackets [sample], signifies a variable to be replaced with the value specific to your situation. This article also uses the schema DBA for event monitors. This can be changed as desired. If changed, replace each occurrence of DBA with your chosen schema.<\/p>\n\n\n\n

The db2pd Utility<\/h2>\n\n\n\n

The db2pd utility is a troubleshooting tool that collects information without acquiring any latches or using any engine resources.<\/p>\n\n\n\n

To get a list of the details for all current locks use:<\/p>\n\n\n

$ db2pd -db [databaseName] -wlocks detail<\/code><\/pre>\n\n\n
For more information:<\/p>\n\n\n\n
https:\/\/www.ibm.com\/docs\/en\/db2\/11.5?topic=tools-db2pd#c0054595<\/a><\/p>\n\n\n\n
Table Functions<\/h2>\n\n\n\n
You can retrieve information about locks using table functions. Information about locks is always available from the database manager. You do not need to enable the collection of this information.<\/p>\n\n\n\n
To see a list of applications holding locks on a specific table, use this statement:<\/p>\n\n\n
SELECT APPLICATION_HANDLE, LOCK_NAME, LOCK_STATUS FROM TABLE (mon_get_locks(CLOB('<table_schema>[schema]<\/table_schema> <table_name>[table]<\/table_name>'),-2));<\/code><\/pre>\n\n\n
For more information:<\/p>\n\n\n\n
https:\/\/www.ibm.com\/docs\/en\/db2\/11.5?topic=mpf-mon-get-locks-table-function-list-all-locks-in-currently-connected-database<\/a><\/p>\n\n\n\n
Event Monitors<\/h2>\n\n\n\n
Pulling information from table functions and the database’s memory sets returns the values of monitor elements at the specific point in time the routine is run. Event monitors allow you to view events historically. Event monitors capture data when an event occurs for later analysis. This means that event monitors need to be created and activated prior to the events occurring.<\/p>\n\n\n\n
The following process explains how to create a locking event monitor that writes to unformatted event tables.<\/p>\n\n\n\n
Prerequisite Setup<\/h3>\n\n\n\n
The locking event monitor performs best with a 32K tablespace, temp tablespace, and bufferpool. It is recommended that you create these if they do not already exist. Here are the commands to create them:<\/p>\n\n\n
CREATE BUFFERPOOL BUFF32K IMMEDIATE \n   SIZE 2500 AUTOMATIC \n   PAGESIZE 32 K;\n\nCREATE LARGE TABLESPACE TAB32K \n   PAGESIZE 32 K \n   BUFFERPOOL BUFF32K \n   DROPPED TABLE RECOVERY ON;\n\nCREATE SYSTEM TEMPORARY TABLESPACE TEMPSYS32K \n   PAGESIZE 32 K \n   BUFFERPOOL BUFF32K;<\/code><\/pre>\n\n\n
The locking event monitor also requires certain parameters to be enabled for collection of needed details. Below are the parameters with their suggested setting:<\/p>\n\n\n\n