|Subject||Re: [firebird-support] Suboptimal plan|
thanks for your answer.
Although the statistics are up to date the optimizer still chooses the shorter stream as the controller.
Nevertheless, I found a workaround using a subquery on the shorter table instead of a join.
This forced the optimizer to traverse the longer table first and boosts the performance even more than using an optimized query with a fixed plan.
Thank you very much for your help.
Are the indexes statistics up to date?
Also, post the query, query plan, and indexes stats.
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ACacacfs> In a select statement there are two tables joined by a single
ACacacfs> matching field, with search conditions in both of them. One of them has
ACacacfs> roughly 130000 records, while the other has 600.
ACacacfs> Inspecting the plan generated by the optimizer, I realized that it
ACacacfs> uses the shorter one as the controlling stream instead of the longer one
ACacacfs> (i.e. the shorter table is at the left side).
ACacacfs> Using a PLAN expression with the corresponding indexes to bypass
ACacacfs> the plan deviced by the optimizer in order to switch the order of the
ACacacfs> streams, the performance is boosted (nearly three times faster).
ACacacfs> What can cause the optimizer to pick a shorter table as the
ACacacfs> controlling stream ?
ACacacfs> Is there a workaround to induce the optimizer to select the streams
ACacacfs> in a fixed way or should I have to resort to a manually imposed PLAN ?