Re: PDQ

Art, I have PSORT_DBTEMP set to /tmp and that is implemented on physical memory, mounted on swap space.Make it, in this case sense to create mutiple directories, /tmp/psort1, /tmp/psort2,.. and set PSORT_DBTEMP to them. I create four indexes in parallel. Does it speeds up to give them all a different filesystem for the sort-work files. Albert H. Wisse "Art S. Kagel" wrote: > wisse wrote: > > > > I noticed a performance decrease instead of a performance increase > > when using PDQ with creating indexes. > > > > The create indexes are done one/with: > > > > * Informix 7.23.UC6 on Solaria 2.5.1. > > * System: SUN E4000 with 6 CPU's and 5.3 GB internal memory. > > * Informix has four CPU, NOAGE is set, AFFINITY is set for all 4 > > Informix CPU's. > > * Tables are fragmented round robbin on two dbspaces. > > * Indexes has their own dbspace and disk/diskchannel > > * All dbspaces are on raw devices > > > > During the creations of indexes nobody is using the system. When using > > PDQ the index creation takes around 10% longer. That is not what I > > want. > > Monitoring onstat -g mgm tells me hat I have PDQ resources enough. And > > other measurements show me that the system has plenty of resources > > left. > > > > The question is this a feature of Informix 7.23.UC6 or do I something > > wrong. > > To take best advantage of parallelism for index creation you also have > to set the PSORT parameters. PDQ wil get you additional scan threads > but not additional sort threads. Use PSORT_NPROCS to set the number of > sort threads used with PDQ (documentation says no more than 12 but I > have seen performance gains with values up to 40). Also since sort > work files are temporary you can take advantage of a quiet filesystem > by placing sort-work files in filesystem space by setting PSORT_DBTEMP > to a list of at least 3 filesystems prefereably on different drives. > This will allow writes to sort-work files at memory speeds rather than > the synchronous writes to even temp dbspaces. > > Art S. Kagel