dictionary cache parameters

I read that the parameters (DD_HASHSIZE * DD_HASHMAX) should be greater than the estimated number of active tables in all databases for performance gains. Where the heck are these parameters? They are not in the onconfig file. Environment variables? Maybe. Any ideas? Also, what's a good way to estimate the number of active tables?

Top Cat wrote: > > I read that the parameters (DD_HASHSIZE * DD_HASHMAX) should be greater than > the estimated number of active tables in all databases for performance > gains. Where the heck are these parameters? They are not in the onconfig > file. Environment variables? Maybe. Any ideas? Also, what's a good way > to estimate the number of active tables? These are undocumented ONCONFIG parameters. You can safely add them to your onconfig file just make sure the DD_HASHSIZE is prime and DD_HASHMAX should be relatively small for best performance. In effect more smaller buckets are better than fewer larger ones. Informix has verified that it is valid to adjust these parameters, along with DS_HASHSIZE/DS_POOLSIZE and PC_HASHSIZE/PC_POOLSIZE the corresponding parameters for data distribution cache and stored procedure cache hash tables. I will never understand why Informix hides these tunables away like this (I just find them and bug 'em until they fess up anyway). Art S. Kagel

In article <37D915D8.AC3A487F@bloomberg.net>, kagel@bloomberg.net wrote: > Top Cat wrote: > > > > I read that the parameters (DD_HASHSIZE * DD_HASHMAX) should be greater than > > the estimated number of active tables in all databases for performance > > gains. Where the heck are these parameters? They are not in the onconfig > > file. Environment variables? Maybe. Any ideas? Also, what's a good way > > to estimate the number of active tables? > > These are undocumented ONCONFIG parameters. You can safely add them to > your onconfig file just make sure the DD_HASHSIZE is prime and DD_HASHMAX> should be relatively small for best performance. In effect more smaller > buckets are better than fewer larger ones. Informix has verified that it > is valid to adjust these parameters, along with DS_HASHSIZE/DS_POOLSIZE > and PC_HASHSIZE/PC_POOLSIZE the corresponding parameters for data > distribution cache and stored procedure cache hash tables. I will never > understand why Informix hides these tunables away like this (I just find > them and bug 'em until they fess up anyway). > > Art S. Kagel So, now that we know about all these nifty parameters, how do we know if we've got them set optimally? My latest status script checks the DD_HASHSIZE and DD_HASHMAX parameters against the total number of dictionary cache entries shown with "onstat -g dic". Basically, I just warn if it gets up to 80%. Have you done any checking on performance using the other parameters, and if so, what do you check and what values are good? -- --Marty Allred "The Rambling Man" Don't believe me? Try reading one of my messages. Sent via Deja.com http://www.deja.com/ Share what you know. Learn what you don't.