On Sat, Jan 19, 2008 at 10:33:00PM -0500, Tom Lane wrote: > The difference comes from the fact that the HashAggregate step --- which > is being done on hashing columns (data, usuario) --- is effectively > reading out in hash-value order for usuario, meaning that that is the > order in which we make index insertions. 8.2 had an extremely chintzy > hash function for integers --- basically just return the negative of the > integer value --- while 8.3 takes it seriously and produces a nicely > randomized hash value. This means that the usuario values are returned > in a relatively well ordered fashion in 8.2 and a nearly totally random > one in 8.3. A random thought: Is there not some way of representing this difference in the planner? We store the correlation for tables, could it not be argued that the output of a hash plan is correlation zero, whereas an indexscan may have higher correlation... A low correlation works against plans returning lots of rows. Have a nice day, -- Martijn van Oosterhout <kleptog@xxxxxxxxx> http://svana.org/kleptog/ > Those who make peaceful revolution impossible will make violent revolution inevitable. > -- John F Kennedy
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