On Tue, Jul 23, 2013 at 1:11 PM, Amit Langote <amitlangot...@gmail.com> wrote: > Hello, > > While understanding the effect of maintenance_work_mem on time taken > by CREATE INDEX, I observed that for the values of > maintenance_work_mem less than the value for which an internal sort is > performed, the time taken by CREATE INDEX increases as > maintenance_work_increases. > > My guess is that for all those values an external sort is chosen at > some point and larger the value of maintenance_work_mem, later the > switch to external sort would be made causing CREATE INDEX to take > longer. That is a smaller value of maintenance_work_mem would be > preferred for when external sort is performed anyway. Does that make > sense? >
Upon further investigation, it is found that the delay to switch to external sort caused by a larger value of maintenance_work_mem is small compared to the total time of CREATE INDEX. So, plotting for a number of maintenance_work_mem values shows that its effect is negligible. Are there any other parts of external sort logic that might make it slower with increasing values of maintenance_work_mem. It seems merge order, number of tapes seem are related with state->allowedMem. Does that mean, external sort is affected by the value of maintenance_work_mem in a way roughly similar to above? -- Amit Langote -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
