On Thu, Apr 13, 2006 at 08:36:09PM -0400, Tom Lane wrote: > Jim Nasby <jnasby@xxxxxxxxxxxxx> writes: > > While working on determining a good stripe size for a database, I > > realized it would be handy to know what the average request size is. > > Getting this info is a simple matter of joining pg_stat_all_tables > > and pg_statio_all_tables and doing some math, but there's one issue > > I've found; it appears that there's no information on how many heap > > blocks were read in by an index scan. Is there any way to get that info? > > If the table is otherwise idle, the change in the table's entry in > pgstatio_all_tables should do, no? Ahh, ok, I see the heap blocks are counted. So I guess if you wanted to know what the average number of blocks read from the heap per request was you'd have to do heap_blks_read / ( seq_scan + idx_scan ), with the last two comming from pg_stat_all_tables. In my case it would be helpful to break the heap access numbers out between seqscans and index scans, since each of those represents very different access patterns. Would adding that be a mess? > (This is as of 8.1 ... older versions acted a bit differently IIRC.) Yeah; I recall that it was pretty confusing exactly how things were broken out and that you changed it as part of the bitmap scan work. -- Jim C. Nasby, Sr. Engineering Consultant jnasby@xxxxxxxxxxxxx Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
