Re: Logical Logs Size

On 18 Nov 98, at 16:16, Mary Curtis wrote: > Forgive me if my question has been discussed recently or repeatedly. > I haven't been able to read this newsgroup for ages, but would > appreicate your input as I have a limited amount of time to research > my questions. Please respond via email if possible, thanks for your > help .... Mary Curtis (mary@rez.com) > > We are running a large OLTP application on a SUN 10000 platform. We > have DLTs (jutebox like) tape media. In the past we have always run > continuous logging to tape (DAT tape drives). Continuous logging to > the DLTs is no longer the preferred method. We plan to run SUN's > NetBackup utility to backup the Informix logs when a pre-determined > number are full. > > Our experience has been with running small sized logical logs in our > continuous logging environment in the past (2k to 8k in size). At > approximately 4k size, our application will fill a log on the system > we are discussing in as little as 2 minutes and in as long as 30 minutes > given the varying times of the day and the load. I assume you mean 2000 to 8000 KB here. Informix does not allow logical logs to be less than 200 KB. > The jutebox can't keep up with the logs filling in minutes, the > storage media is meant for less often backups, but to stream a lot of > information quickly to the tapes. > > The primary question, HOW BIG TO MAKE THE LOGICAL LOGS? Our system > administration group would like to see 50 megabyte logs. That's way > too much shared memory for me, or is it?? I don't think it is. It's important to differentiate between the logical logs and their buffers. The logical logs exist on disk, the buffers in shared memory. So you can make your logical logs as big as just under 2GB a piece, provided you have enough disk space available. > I'm looking for experience and recommendations on suggested "larger" > sized logs. Please also comment on the following concerns if you can: > > - shared memory (allocating to a bundle to large logs?) > - long transactions (increasing the log sizes, have you decreased > the long transaction high water marks? We're > at 50/60 for LTXHWM/LTXEHWM) > - recovery (as long as checkpoints are in line, are you > safe? I've been in recovery on a long > transaction and hence my concern above about > rolling back forever and a day on a long txn) Chances are that you need either more logs and/or bigger logs if you get a long transaction. > - checkpoints (any special considerations? We currently > checkpoint at 150secs, duration usually 0-3 > seconds, no complaints) > - physical log size (any special considerations when increasing > logical log size?) > > Anything else you think of, please share your experience. While you're about it, move your logical logs and physical log out of rootdbs and into separate dbspaces on separate devices, preferably with separate controllers. It's difficult to make informed comments on the other issues without knowing a lot more about your transactions and data volume. Still, HTH. -- Ciao, Billy "Give a man a match and he's warm for an hour, set him on fire and he'll be warm for the rest of his life!"