TMF Planning and Configuration Guide (H06.05+)

Reconfiguring Transaction Limits
HP NonStop TMF Planning and Configuration Guide—540136-002
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Avoiding Runaway Transactions
You can dynamically modify the autoabort threshold to accommodate variations in the
type of transaction activity being performed. During normal business hours, for
example, when the workload consists primarily of OLTP transactions, you might set the
autoabort threshold to a value less than five minutes. In the evening or at night, when
batch processing occurs, you might then change the autoabort threshold to an hour or
more.
Avoiding Runaway Transactions
A runaway transaction is a transaction that, because of an application error, makes
changes to a very large number of records in a database. The autoabort threshold, if
set to a reasonably small time limit, minimizes both the duration of runaway
transactions and the magnitude of their effects.
If the autoabort function is off, however, or if it is on with a large time limit (several
hours, for example), a runaway transaction could generate a very large amount of audit
information and span many audit-trail files. This combination of effects pins audit-trail
files on disk and eventually causes TMF to run out of audi-trail space. If the operator
aborts a runaway transaction that has generated a large number of audit records over
several hours, the backout process then creates many more audit records, making the
situation much worse.
To reduce the risk of runaway transactions, you should enable the autoabort function,
giving it a time limit of not more than five minutes. In a high-volume OLTP
environment, 30 seconds might be appropriate. In lower-volume OLTP or query
environments, three minutes might be more appropriate.
If a runaway transaction occurs, you can recover from it by using the file recovery
feature, specifying the date and time immediately before the runaway transaction
began.
Limits on the Number of Active Transactions
Two configurable limits control the number of active transactions in the HP NonStop
server:
•
The limit for active transactions in the system
•
The limit for active transactions per processor
Each limit consists of a pair of configurable threshold values that, when reached,
trigger the disabling or reenabling of new transactions. You can change these limits by
Note. Changes in the autoabort threshold apply only to new transactions and not to
transactions already in progress. Therefore, the autoabort threshold is a preventive measure,
and not a recovery method, for runaway transactions.