Initiating Checkpoints manually

Hello friends, I want to tune the checkpoint duration by trying different values for the ckptintvl. But as we need to initialise shared memory after each change I am planning to initiate checkpoints manually by writing some shell as below onmode -csleep 50 What do you say? Is it ok? Has anyone faced any problems in this? Thanks in advance Vinod Bhansali Informix DBA DSL Transportation ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com

Vinod Bhansali wrote: > Hello friends, > > I want to tune the checkpoint duration by trying different values for the > ckptintvl. CKPTINTVL is not normally used to tune one's checkpoint duration, although in theory, like the physical log size, it can be used. Rather, in the tuning perspective, it provides a means of balancing disk writes against duration of Fast Recovery. One's checkpoint duration, keeping OS/Hardware/Db space layout variables constant, is primarily dependant on the number of dirty buffers at checkpoint time - those have to be flushed to disk and it is this process which takes time. The number of dirty buffers, in turn, is primarily dependant on 3 onconfig parameters - LRU_MAX_DIRTY, LRU_MIN_DIRTY and BUFFERS. You should be fiddling with LRU_MAX_DIRTY & LRU_MIN_DIRTY to tune your checkpoint duration. Unfortunately, that does require you to bounce your engine. Rudy > But as we need to initialise shared memory after each change I am > planning to initiate checkpoints manually by writing some shell as below > > onmode -c> sleep 50 > > What do you say? Is it ok? Has anyone faced any problems in this? > > Thanks in advance > Vinod Bhansali > Informix DBA > DSL Transportation > ________________________________________________________________________ > Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com

In addition to Rudy's suggestion note that LRUS, CLEANERS, and (if you are not using KAIO) NUMAIOVPS will also affect checkpoint duration far more readily than CKPTINTVL. Also setting the CKPTINTVL too short can adversely affect performance as too large a percentage of time is spent on checkpoints. Art S. Kagel Vinod Bhansali wrote: > > Hello friends, > > I want to tune the checkpoint duration by trying different values for the > ckptintvl. But as we need to initialise shared memory after each change I am > planning to initiate checkpoints manually by writing some shell as below > > onmode -c> sleep 50 > > What do you say? Is it ok? Has anyone faced any problems in this? > > Thanks in advance > Vinod Bhansali > Informix DBA > DSL Transportation > ________________________________________________________________________ > Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com