Is this what you were referring to, Jeff?
derby.language.logQueryPlan
Function
When this property is set to true, Derby writes the query plan information into the derby.log file for all executed queries.
This property is useful for debugging to know what query plan was chosen by the optimizer.
On 1/12/06, Jeffrey Lichtman <[EMAIL PROTECTED]> wrote:
>What can be done about this? It looks like FromVTI.java implements
>Optimizable, which I'm assuming is the interface to supply indexed
>lookup. But, like I said, my head is swimming trying to figure out
>if I either 1) don't understand how to enable an indexed lookup for
>my VTI or 2) if it's not even possible to do so, in which case I
>should start to hack in that ability.
The optimizable interface does not guarantee indexability - it's
simply the interface that the optimizer uses to consider a table
(virtual or not) in the optimization process.
When I left the Cloudscape/Informix/Derby project, indexable VTIs had
not been implemented, and I believe the feature is still
unimplemented. It would be a useful feature, but would take a lot of work.
Rather than try to get indexing to work on VTIs, I'd consider why the
query optimizer isn't using a hash join strategy, which would
probably give much better performance than the Cartesian product
you're getting now. The optimizer should consider hash join on a VTI
if it is the inner table of the join and it is materializable - that
is, if the parameters to the constructor of the VTI are
query-invariant. So, for example, if the params are all constants,
hash join should be considered, but if any parameter uses a column
from the joining table, hash join cannot be considered. Also, hashing
can be done only on equijoins.
There are trace flags to help you figure out what the optimizer is
doing. The trace output is voluminous but very helpful in diagnosing
problems like this. I don't remember how to activate optimizer
tracing - a little help, anyone?
- Jeff Lichtman
[EMAIL PROTECTED]
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