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Object documentation LOGBUFF (Informix)  Locate the document in its SAP Library structure

Definition

The LOGBUFF parameter of the Informix ONCONFIG file specifies the size in kilobytes (KB) of each of the logical-log buffers in shared memory. Multiple buffering permits user threads to write to the active buffer while one of the other buffers is being flushed to disk. The size of a buffer determines how often or quickly it fills and therefore how often it must be flushed to the logical-log file on disk.

The database server uses the LOGBUFF parameter to set the size of internal buffers that are used during recovery. If you set LOGBUFF too high, the server can run out of memory and shut down during recovery.

Use

For up-to-date recommendations, see SAP Note 41360.

You can check whether the set size is sufficient for your system by checking the log buffers in the overview screen of the database monitor or with the command onstat –l .

Log.Log Written/IO should be at least 75 % of Logical Log Buf. If not, we recommend you to change the LOGBUFF parameter and watch the change in the value of Log.Log Written/IO.

Example

This is an example of the output from onstat –l :

Logical logging

Buffer

bufused

bufsize

numrecs

numpages

numwrits

recs/pages

pages/io

L-1

0

8

5898609

898878

358944

6.6

2.5

If you use a logical volume manager (LVM) with disk striping, you can optimize performance by adapting the buffer size to the stripe size. In this case, you do not need to follow the recommendation above.

 

See also:

Log Buffers (Informix)