Kbase P27294: What is the -Mf parameter?
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
6/19/2003 |
|
Status: Unverified
GOAL:
What is the -Mf parameter?
FIX:
The following is extracted from the documentation.
Delayed BI File Write (-Mf)
Usage: -Mf n
n is the value in seconds of the delay before the database engine synchronously writes to disk the last before-image (BI) file records at the end of each transaction. It also specifies the interval that the broker process wakes up to make sure all BI file changes have been written to disk. The default is 3 for single-user batch jobs and for multi-user databases using shared memory. Otherwise, the default is 0. The maximum value is 32768.
Use Delayed BI File Write (-Mf) to improve performance on a heavily loaded system. Using -Mf does not reduce database integrity. However, if there is a system failure, it is possible the last few completed transactions will be lost (never actually written to the BI file).
When running with full integrity, at the end of each transaction the database engine does a synchronous write to disk of the last BI file block. This write guarantees that the completed transaction is recorded permanently in the database. If the user is notified that the transaction has completed and the system or database manager crashes shortly afterwards, the transaction is not lost.
Do not set -Mf on a lightly loaded system with little database update activity. Under these conditions, the extra BI write is very important and does not impact performance. On a heavily loaded system, however, the BI write is less important (the BI block will be written to disk very soon anyway), and has a significant performance penalty. Setting -Mf to delay this extra BI write saves one write operation per transaction, which can significantly improve performance. The extra BI file write is delayed by default for batch jobs.
If -Mf is set to a positive value, the last BI file record is only guaranteed to be written out to disk when a user logs out, or when the server or broker process terminates normally. On multi-user systems, the n argument determines the oldest completed transaction that can be lost.