Subject | RE: [firebird-support] Firebird 2.0 performance issue |
---|---|
Author | Dmitry Yemanov |
Post date | 2006-08-03T13:05:06Z |
[re-sent]
Andrew,
This is one of the cases where it's hard to improve something without making
something other worse :-) The new v2.0 cost estimation algorithm considers
indices on s.type_id and l.action_id worth using, whilst FB 1.5 ignored
them. And in this case 1.5 was more correct, unfortunately. I don't see any
easy way to fix this situation, so the only good solution for 2.0 would be
"hints" like:
s.type_id+0 = i.type_id
-- and
l.action_id+0 = a.id
that disable usage of the "bad" indices.
We'll try to fix/enhance the cost estimation rules in the next version, so
it would perform better in such cases.
Dmitry
Andrew,
This is one of the cases where it's hard to improve something without making
something other worse :-) The new v2.0 cost estimation algorithm considers
indices on s.type_id and l.action_id worth using, whilst FB 1.5 ignored
them. And in this case 1.5 was more correct, unfortunately. I don't see any
easy way to fix this situation, so the only good solution for 2.0 would be
"hints" like:
s.type_id+0 = i.type_id
-- and
l.action_id+0 = a.id
that disable usage of the "bad" indices.
We'll try to fix/enhance the cost estimation rules in the next version, so
it would perform better in such cases.
Dmitry