Ree: onmode -B

We now are down to 0 or 1 seconds for checkpoints....Much better. Great advice! - It seems to work very well so we will go with it...... Thnaks again Jonathan Leffler <jleffler@earthlink.net> wrote in message news:<3EEA8F90.9030309@earthlink.net>... > tomL wrote: > > apparently, onmode -B is an undocumented feature that many people use. > > > > We are running informix 9.21 HC5-1 on UNIX-HP ver 11.00 and have > > employed the contorted method of running a cron job that fires onmode > > -B, sleeps for 2, then runs onmode -c. It has taken our long & painful > > checkpoints that use to last anywhere from 20-132 seconds (!) and > > dropped checkpoints to 1 second - a remarkable improvement. What I > > would like to know is if anyone know if there is a price to pay for > > doing this? > > The complexity of running the cron job - mainly. This technique does > not clear the buffer pool completely (as Ravi - rkusenet - implied); > it simply writes out all the dirty pages (marking them as clean). The > pages in the buffer pool do not have to be re-read to be re-used. > > There is a small potential penalty; your users might modify a page > between the time when the onmode -B flushes it and the time of the > checkpoint proper; that page will be written twice in short > succession, which would not have happened without the onmode -B. On > the other hand, this minor penalty is usually more than offset by the > reduced duration of the checkpoint proper. > > As Ravi also pointed out, there is a slight chance that something > weird could happen and overfill the physical log (75%) or otherwise > trigger a checkpoint. However, by setting the checkpoint interval to, > say, 10 minutes and running the cron job every 5 minutes, and by > sizing your system appropriately, you can pretty much avoid those > problems. You might have problesm if the cron job stops working - but > then the automatic systems would kick in and do checkpoints anyway, > just more slowly. > > > We currently have a case in Informix support and have not heard > > anything back yet so we are going with this "solution" for now because > > it is really needed. > > > Go with what works for you.