[EMAIL PROTECTED] (Joseph Bove) writes: > I do a rather simple query: select count (*) from large-table where > column = some value; > > About 80% of the time, the response time is sub-second. However, at > 10% of the time, the response time is 5 - 10 seconds.
Does it seem data-dependent? That is, does the time vary for different values of "some value?" If a particular value is particularly common, the system might well revert to a sequential scan, making the assumption that it is quicker to look at every page in the table rather than to walk through Enormous Numbers of records. I had a case very similar to this where a table had _incredible_ skewing of this sort where there were a small number of column values that occurred hundreds of thousands of times, and other column values only occurred a handful of times. I was able to get Excellent Performance back by setting up two partial indices: - One for WHERE THIS_COLUMN > VITAL_VALUE; - One for WHERE THIS_COLUMN < VITAL_VALUE; The REALLY COMMON values were in the range < VITAL_VALUE. -- output = ("cbbrowne" "@" "libertyrms.info") <http://dev6.int.libertyrms.com/> Christopher Browne (416) 646 3304 x124 (land) ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings