Re: tuning questions

Mark D. Stock wrote: A whole lot of good stuff. I like to see that ;-) I just wanted to emphasize: > > I cannot seem to get my onstat -F LRU write / Chunk Write ratio > > any higher than 1:1 or 1.5:1. During the day my checkpoints average > > only 3-4 seconds: > > > > but at night when a lot of batch processing is occurring (beginning at > > 3:30 AM for instance) they go up to 30-40 seconds, or even higher: > > A long checkpoint for DSS environments is normal. Remember, chunk writes > are the most efficient. If you don't have a problem with your 3-4 second checkpoints during the day, and only batch jobs are running at night, this probably isn't a problem. Long checkpoints are mainly a problem when OLTP users are on, because it means they can't write anything until the checkpoint is completed, and waiting 40 seconds for the checkpoint to complete can seem like an eternity. If the only things going at night are batch jobs, they won't get upset with the 40 second delay. The long checkpoint doesn't mean that your overall throughput is lower -- it may even be higher. It's just more uneven, with the 40 second pauses for checkpoints. As Mark said, chunk writes are done more efficiently (all the pages for a specific chunk are sorted and written together -- minimizes head movement) than LRU writes; it's just that the OLTP users waiting for their screen to return don't necessarily care about efficiency as much as about short response times. > > (As an aside, why would a checkpoint not occur for 16 minutes between > > 3:15 and 3:31 when my CKPTINTVL is 300???) > > No one did any work? Right. Usually gaps like this are because there was no activity. No point in checkpointing if there was no activity. > > My ontape -s lev 0 archives are taking a *LONG* time, like 5 or 6 > > hours. What could be causing this? > > The tape block size? Find out what the tape drive supports, and set it > as large as possible. Use RAW disk. Make sure temp dbspaces are on RAW > disk. Slow tape drive? Lots of data? How long were you *expecting* it to take? June -- june_t@hotmail.com Lost in the wilds of Palo Alto, living on sushi