Qi Huang wrote: > I need to estimate the hashjoin cost in my research.
> I looked at the code of final_cost_hashjoin() . It is not clear > what factor it is considering. So, except the I/O to and from disk, > what other factors are affecting the cost of hahsjoin? http://www.postgresql.org/docs/9.2/interactive/runtime-config-query.html#RUNTIME-CONFIG-QUERY-CONSTANTS If you don't find it practical to read the code, you could run ANALYZE of a query which uses a hashjoin with different cost factors (these can be changed for your current connection with the SET command) and observe the cost numbers in the output. > Also, is there any way to force postgres abide on the estimation of > Hashjoin cost as 3(R+S), which also means, to make hashjoin cost > mainly spend on I/O? How useful would that be for workloads where data is fully cached? -Kevin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
