HP NonStop G-Series - Manual (Page 52)

Configuring Automatic Transaction Processing
HP NonStop AutoTMF Software User’s Guide—429952-014
4-6
Transaction Commit
Transaction Commit
To commit an automatic transaction, NonStop AutoTMF software analyzes all file-
access operations. File locking, record locking, and update operations are the primary
factors that determine when automatic transactions may be committed.
Unaudited file-locking behavior and record-locking cannot be replicated when
performing operations on audited files, but NonStop AutoTMF software ensures that
normal, unaudited, file-locking behavior and record-locking behavior are observed.
NonStop AutoTMF software ensures that the database does not become inconsistent
by preventing the premature unlocking of files and records. When the application has
logically unlocked records and files, NonStop AutoTMF software can safely commit
automatic transactions.
Automatic transactions are committed by a proprietary set of processing rules, driven
by the following activities and events:
•
Process operations that lock, update, and unlock files and records; such
information determines both the lock protocols that need to be preserved and the
actual lock state of open files.
•
Process operations that signal a requirement or an opportunity to commit an
automatic transaction. For example, when a server process replies to a requestor:
the server has performed database operations for one request and will await a new
request; any outstanding automatic transaction should be committed at this point.
•
Process operations, such as termination, that would cause automatic transactions
to be aborted.
•
Process operations that may require a commit to isolate automatic transactions
from external effects, as described in
Transaction Isolation on page 4-7
•
Time that an automatic transaction has been alive; you can configure the maximum
transaction lifetime to a reasonable interval that is consistent with good
performance
•
Amount of update activity performed under an automatic transaction; you can
configure the maximum number of updates in a transaction to keep the transaction
overhead to a reasonable fraction of the total processing cost.
Transactions that are used for a large number of updates accumulate locks, cause
other resource problems, and have a larger impact if aborted unilaterally.
Transactions tend to increase the time during which locks are held and this increased
time may result in increased lock contention. This phenomenon is common in all
transaction-based database systems. Lock contention can be monitored by using the
NonStop AutoTMF LISTLOCKS command.
Excessive lock contention can be reduced through proper NonStop AutoTMF
configuration, but changes in the configuration may cause more frequent transactions
and a corresponding increase in processing requirements.