In IDMS Perfmon realtime monitor (PMRM) Active User Task Detail , if a task is in a WAIT state it will show the ECB(s) the task is waiting for.
Sometimes we see an ECB type of 'SPACE'.
What does this mean?
ECB type SPACE means Page Space Lock.
If a task indicates it is waiting for ECB 'SPACE' you will see a Waited-On DBKEY indicating Line number 0 which is the SR1 record in the DB Page header.
Example: 10030095: 0
When a transaction needs to STORE or ERASE a record on a page, or MODIFY a Variable Length Record that changes record length, the transaction must first acquire a lock on the Page Space Available count, then it can do the update to the record and once the update operation is complete the Page Space lock is freed.
Update locks on any records updated are held until COMMIT or FINISH, but Page Space locks are freed as soon as the update operation completes.