On Friday 17 July 2009 11:12:41 Jan-Ivar Mellingen wrote:
> One of our customers discovered that by replacing <>TRUE with =FALSE in
> a query of a table containing 750.000 records reduced the query time
> from about 12 seconds to about 60 milliseconds!
> This is a dramatical difference, but I cannot understand why. In my head
> "<>TRUE" should behave exactly the same as "=FALSE". This looks like a
> bug to me, or am I overlooking something?
The planner just isn't that smart. The boolean type is a special case where
<> some_value implies = some_other_value, but this doesn't generalize well to
other data types. And the planner doesn't have a whole lot of data type
specific knowledge.
I think a better index definition might actually be on alarm_status, with a
partial index predicate on logg_avsluttet = false.
