Is there a way to determine a reasonable value for random_page_cost via some testing with OS commands. We have several postgres databases and determining this value on a case by case basis may not be viable (we may have to go with the defaults) On Fri, Jun 11, 2010 at 5:44 AM, Kenneth Marshall <ktm@xxxxxxxx> wrote: > Hi Anj, > > That is an indication that your system was less correctly > modeled with a random_page_cost=2 which means that the system > will assume that random I/O is cheaper than it is and will > choose plans based on that model. If this is not the case, > the plan chosen will almost certainly be slower for any > non-trivial query. You can put a 200mph speedometer in a > VW bug but it will never go 200mph. > > Regards, > Ken > > On Thu, Jun 10, 2010 at 07:54:01PM -0700, Anj Adu wrote: >> I changed random_page_cost=4 (earlier 2) and the performance issue is gone >> >> I am not clear why a page_cost of 2 on really fast disks would perform badly. >> >> Thank you for all your help and time. >> >> On Thu, Jun 10, 2010 at 8:32 AM, Anj Adu <fotographs@xxxxxxxxx> wrote: >> > Attached >> > >> > Thank you >> > >> > >> > On Thu, Jun 10, 2010 at 6:28 AM, Robert Haas <robertmhaas@xxxxxxxxx> wrote: >> >> On Wed, Jun 9, 2010 at 11:17 PM, Anj Adu <fotographs@xxxxxxxxx> wrote: >> >>> The plan is unaltered . There is a separate index on theDate as well >> >>> as one on node_id >> >>> >> >>> I have not specifically disabled sequential scans. >> >> >> >> Please do "SHOW ALL" and attach the results as a text file. >> >> >> >>> This query performs much better on 8.1.9 on a similar sized >> >>> table.(althought the random_page_cost=4 on 8.1.9 and 2 on 8.4.0 ) >> >> >> >> Well that could certainly matter... >> >> >> >> -- >> >> Robert Haas >> >> EnterpriseDB: http://www.enterprisedb.com >> >> The Enterprise Postgres Company >> >> >> > >> >> -- >> Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) >> To make changes to your subscription: >> http://www.postgresql.org/mailpref/pgsql-performance >> > -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
