Carlos Moreno wrote: > That is: the first time I run the query, it has to go through the > disk; in the normal case it would have to read 100MB of data, but due > to bloating, it actually has to go through 2GB of data. Ok, but > then, it will load only 100MB (the ones that are not "uncollected > disk garbage") to memory. The next time that I run the query, the > server would only need to read 100MB from memory --- the result should > be instantaneous...
Wrong. If there is 2GB of data, 1900MB of which is dead tuples, those pages would still have to be scanned for the count(*). The system does not distinguish "pages which have no live tuples" from other pages, so it has to load them all. -- Alvaro Herrera http://www.amazon.com/gp/registry/CTMLCN8V17R4 "[PostgreSQL] is a great group; in my opinion it is THE best open source development communities in existence anywhere." (Lamar Owen) ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
