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IDS Forum

Re: query sqlexplain interpretation

Posted By: Juan Francisco González Navarro
Date: Wednesday, 5 November 2014, at 12:08 p.m.

In Response To: Re: query sqlexplain interpretation (Art Kagel)

Thnank you. I'll try

2014-11-05 16:45 GMT+00:00 Art Kagel <art.kagel@gmail.com>:

> Your data distributions are stale or non-existent. Look at the detail for
> the first table (t1) in the timing section. The optimizer estimated that
> this phase would return one row. However, it read through 1,640,606 rows
> and actually returned 1,422,778 rows.
>
> The second table (t2) is estimated to return one row as well, but it
> actually scanned 1,422,337 rows that matched the rows from t1 and selected
> all of them to join.
>
> The third table (t3) again estimated one row but matches 1,422,337 row in
> the join to t1+t2 and filtering removed all but 40 rows which were actually
> returned not the one row the optimizer estimated.
>
> All this means that the optimizer got bad information from your data
> distributions and so probably chose the wrong indexes and the wrong join
> order. It probably should have searched t3 first.
>
> Fix? Update statistics using the recommended protocols described in the
> Performance Guide or as they are implemented using my dostats_ng.ec
> utility. Dostats is included in the utils2_ak package which you can
> download from the IIUG Software Repository (www.iiug.org/software) for
> free.
>
> If you have not disabled AUS, then it is not configure properly to maintain
> stats for you. I maintain that dostats does a better job than AUS, but
> even up-to-date AUS, correctly configured, distributions are better than
> what you have now.
>
> Art
>
> --089e0160b9ca0db21505071f4d74
>
>
>
> *******************************************************************************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

--089e01184afec2db1605071f9f9d

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