Re: which is more important? freq of checkpoints or the duration of them?

On Mon, 3 Mar 2008, Douglas J Hunley wrote:

> In other words, is it ok to checkpoint say, every 5 minutes, if it only
> last a second or three or better to have checkpoints every 10 minutes
> that last half a minute?

When checkpoints do too much work at once they will block clients for a
significant period of time near the end--anywhere from 2 to 8 seconds
isn't unusual.  Every client on the system will just hang, then they all
start responding again in a batch when the checkpoint is finished.

With that as the problematic case, if you can keep the duration of the
checkpoint processing minimal by having them happen more frequently, then
that's the better approach.  You can't push that interval too small though
or your system will be continuously checkpointing.

In cases where checkpoints hurt no matter how often you do them, there it
makes sense to have them as infrequently as possible so at least you
minimize the number of times that the disruption happens.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD