"Josh Berkus" <josh@xxxxxxxxxxxx> writes: > Simon, > >> There is an optimum for each specific sort. > > Well, if the optimum is something other than "as much as we can get", then we > still have a pretty serious issue with work_mem, no? With the sort algorithm. The problem is that the database can't predict the future and doesn't know how many more records will be arriving and how out of order they will be. What appears to be happening is that if you give the tape sort a large amount of memory it keeps a large heap filling that memory. If that large heap doesn't actually save any passes and doesn't reduce the number of output tapes then it's just wasted cpu time to maintain such a large heap. If you have any clever ideas on how to auto-size the heap based on how many output tapes it will create or avoid then by all means speak up. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Get trained by Bruce Momjian - ask me about EnterpriseDB's PostgreSQL training!
