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  1. MariaDB Server
  2. MDEV-6215

Range Analyzer should tell whether range is looser than the source condition

        Details

        • Type: Task
        • Status: Open
        • Priority: Minor
        • Resolution: Unresolved
        • Fix Version/s: 10.1
        • Component/s: None

          Description

          (filed based on discussions with Igor)
          Cost estimation code makes use of range analyzer to match (parts of) the WHERE
          condition against column's Histogram.

          Some other module (todo: which? MDEV#?) needs to know whether the estimate is
          precise or not.

          The main source of imprecision is that some of conditions are not [fully]
          sargable. That is, range analyzer produces ranges that are wider than the
          supplied conditions.

          Examples of conditions with imprecise estimates:

            t.col < 10 AND t.col MOD 3 = 2 
  t.col LIKE 'foo%bar%'

          Examples of conditions with precise estimates:

            t.col LIKE 'foo%'
  t.col < 3214
  t.col = 'bar'
  t.col IN (1,2,3) OR t.col BETWEEN 10 AND 20

          (TODO: we don't need to handle the case of multi-column range analysis, do we?)

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                  • Assignee:
                    Unassigned
                    Reporter:
                    psergey Sergei Petrunia
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                    • Created:
                      Updated: