log_checkpoint_timeout

[gsprince]

Hi:

I recently changed my "log_checkpoint_timeout" init.ora parameter to 0 . After restarting the instance, it has the value of 900. Does any one knows, how oracle arrives at this number? Or is it the default value?

I am running Oracle 8.1.6 on Linux.

Thanks,

[sambavan]

It is a default value on oracle 8i and it is 1800 seconds in Enterprise Edition. Looks like oracle enforces its recomendation of not to set the value as 0

Sam

[wren01]

maybe it's default for LINUX, on HP-UX and NT, it's OK to set to 0.

[gsprince]

Sambhavan!

Doesn't Oracle recommend "LOG_CHECKPOINT_INTERVAL" to "LOG_CHECKPOINT_TIMEOUT"?

I knew with 8i the meaning of these parameters have changed but haven't gone in detail.

Thank you all,

[sambavan]

Originally posted by gsprince
Sambhavan!

Doesn't Oracle recommend "LOG_CHECKPOINT_INTERVAL" to "LOG_CHECKPOINT_TIMEOUT"?

Thank you all,

Here is what the recomendation that oracle gives under its tuning.


How Checkpoints Affect Performance

Aggressive checkpointing will write dirty buffers to the datafiles more quickly and can reduce instance recovery time in the event of an instance failure. If checkpointing is fairly aggressive, then replaying the redo records
in the redo log between the current checkpoint position and the end of the log involves processing relatively few data blocks. This means that the roll-forward phase of recovery will be fairly short.

However, aggressive checkpointing can reduce run-time performance, because checkpointing causes DBWn processes to perform I/O. The overhead associated with checkpointing is usually small.

Adjusting Checkpointing Activity

Adjust your checkpointing activity based on your performance concerns. If you are more concerned with efficient run-time performance than recovery time, then set checkpointing to be less aggressive.

If you are more concerned with having fast instance recovery than with achieving optimal run-time performance, then increase the checkpointing interval.

Checkpointing behavior can be influenced by the following parameters:

Set the value of the LOG_CHECKPOINT_INTERVAL initialization parameter (in multiples of physical block size of OS) to be larger than the size of your largest redo log file.

Set the value of the LOG_CHECKPOINT_TIMEOUT initialization parameter to zero. This value eliminates time-based checkpoints.

Set the value of FAST_START_IO_TARGET to zero to disable fast-start checkpointing. This is described below under the heading, "Fast-Start Checkpointing".

In addition to setting these parameters, also consider the size of your log files. Maintaining small log files can increase checkpoint activity and reduce performance.


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Sam