[jira] [Created] (CALCITE-3709) Use "rejected row count" for RelOptCost#getRows

["Vladimir Sitnikov (Jira)" <ji...@apache.org>]

Vladimir Sitnikov created CALCITE-3709:
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             Summary: Use "rejected row count" for RelOptCost#getRows
                 Key: CALCITE-3709
                 URL: https://issues.apache.org/jira/browse/CALCITE-3709
             Project: Calcite
          Issue Type: Improvement
          Components: core
    Affects Versions: 1.21.0
            Reporter: Vladimir Sitnikov


Current cost#rows has a problem: it does not add well when computing cumulative cost.

So the idea is to use the number of _rejected_ rows.

Then the field would have certain meaning:
* If the value is high, the plan is probably rejecting a lot of unrelated rows, thus it is suboptimal
* Extra Project/Calc nodes won't artificially increase rows in the cost fields. Currently each Project adds "rows" which is not very good.
* It is clear what to put to the rows field: "rejected rows" is more-or-less understandable. For Project it would be 0.
* Join/Filter/Calc nodes would show "estimated number of returned rows=X (from metadataquery), rejected rows=Y (from cost)" which would help understanding where the time is spent

That is inspired by PostgreSQL's "rows removed by filter" when running explain analyze (which is statement execution + collecting statistics on each execution plan node):
http://wiki.postgresql.org/wiki/What's_new_in_PostgreSQL_9.2#Explain_improvements



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