Lock shared data

By definition, all database files can be used by many users at the same time. However, some operations can lock the file, member, or data records in a member to prevent them from being shared across jobs.

When the file, member, or record is locked, no other job can read the same data for update operations, which keeps another job from unintentionally deleting the first job's update.

You can lock a row in iSeries™ Navigator by opening a table and editing the row you want to lock, or use the SQL LOCK TABLE statement. You can also use the following operations to lock files, members, or data records, and display locked records using the Display Record Locks (DSPRCDLCK) command or iSeries Navigator.

• Lock records
  DB2 Universal Database™ for iSeries has built-in integrity for records. For example, if PGMA reads a record for update operation, it locks that record. Another program cannot read the same record for update operation until PGMA releases the record, but another program can read the record just for inquiry.
• Lock files
  Some file operations exclusively allocate the file for the length of the operation. When the file is allocated exclusively, any program trying to open the file has to wait until it is released. However, you can set a wait time for the file to become available using the WAITFILE parameter .
• Lock members
  Member operations (such as add and remove) automatically allocate the file exclusively enough to prevent other file operations from occurring at the same time. Input/output operations on the same member cannot be run, but input/output operations on other members of the same file can run at the same time.
• Lock record format data
  Sometimes you might want to lock the entire set of records associated with a record format (for example, all the records in a physical file). In this case, you can use the RCDFMTLCK parameter on the Override Database File (OVRDBF) command.
• Database lock considerations
  Listed here are the commonly used database functions and the types of locks they place on database files.
• Display locked rows using iSeries Navigator
  Use this procedure to display locked rows using iSeries Navigator.
• Display locked records using the Display Record Locks (DSPRCDLCK) command
  You can also use the Display Record Locks (DSPRCDLCK) command to display the current lock status (wait or held) of records for a physical file member.