Re: RA, bugs, and performance

Andreas Zeugswetter wrote: > >> RA_PAGES 150 > >> RA_THRESHOLD 75> >> > >> While these numbers were a bit high, we were able to take advantage of > >> most of the pages that were read-ahead. > >> > > > >Wow, that's way too high for even a DSS environment. Rule of thumb I use > >isto set these to about 32, 16 for a good sized DSS and to about 12,8 for an > >OLTP envrionment. > > Hmm, what you say can only be true on a system very low on memory. > Our values are RA_PAGES 256 and RA_THRESHOLD 96 and we get very > good values with this. On the contrary, for DSS I consider these values still > rather low. > So when you hit the RA_THRESHOLD and there is a read request, you'll bereading 256 pages before your query can continue. As I previously mentioned, that was just a rule of thumb and has worked for me in most of the cases. I guess it all depends on the particular instance. See if you get any different performance, both query and cache, if you set them to lower values. I'm curious. Arun > Andreas Zeugswetter