TMF Introduction (G06.26+)

Transaction Coordination
HP NonStop TMF Introduction—522414-002
2-10
Locking Mechanism
Each server process tries to satisfy the request by performing an appropriate operation
on the database. After satisfying the request, the server replies with a message
indicating the disposition of the request.
For NonStop OS requesters outside the Pathway environment, the requester sends a
message to the server via a WRITEREAD system procedure. WRITEREAD includes
the current transaction identifier with the message, and it becomes the current
transaction of the server as well. The server performs the database access and replies
to the requester.
In addition to managing the begin and end or abort transaction operations, TMF
manages all access to audited data in transactions through the locking mechanism.
Locking Mechanism
TMF provides a locking mechanism that isolates transactions from one another.
Applications protected by TMF make requests for locks on data they read and update.
TMF and the file system together manage the locks.
Locks have these characteristics:
•
Locks are owned by the transaction, not by the processes that initiate database
access.
•
Locks are held on all rows (records) inserted by a transaction.
•
Locks are held on all rows changed or deleted by a transaction.
•
Locks can be held on rows that are read-only, provided a program requests locks.
•
Locks remain in effect until a transaction is fully committed or backed out.
Because of the TMF locking mechanism, a transaction can be backed out without
affecting other concurrent transactions.