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  1. MariaDB Server
  2. MDEV-29577

Rebase 10.7-selectivity tree

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    Details

    • Type: Task
    • Status: Open (View Workflow)
    • Priority: Major
    • Resolution: Unresolved
    • Fix Version/s: 10.12
    • Component/s: Optimizer
    • Labels:
      None

      Description

      The branch: bb-10.11-selectivity

      Also making another review pass while doing this.

      Findings

      > commit a91f4f7d6e676644b349a63995ff8856e5081bce
      > Author: Monty <monty@mariadb.org>
      > Date:   Mon Nov 1 12:34:24 2021 +0200
      >
      >     Update row and key fetch cost models to take into account data copy costs
      

      This change in table_elim.result exposes a bug:

      @@ -562,10 +562,7 @@ LEFT JOIN t1 ON t4.f1 = t1.f1
       JOIN t5 ON t4.f3 ON t3.f1 = t5.f5 ON t2.f4 = t3.f4
       WHERE t3.f2 ;
       id     select_type     table   type    possible_keys   key     key_len ref     rows    Extra
      -1      SIMPLE  t3      ALL     NULL    NULL    NULL    NULL    2       Using where
      -1      SIMPLE  t5      ref     f5      f5      5       test.t3.f1      2       Using where; Using index
      -1      SIMPLE  t4      ALL     NULL    NULL    NULL    NULL    3       Using where
      -1      SIMPLE  t2      ALL     f4      NULL    NULL    NULL    11      Using where; Using join buffer (flat, BNL join)
      +1      SIMPLE  NULL    NULL    NULL    NULL    NULL    NULL    NULL    Impossible WHERE noticed after reading const tables
       # ^^ The above must not produce a QEP of t3,t5,t2,t4
       #    as that violates the "no interleaving of outer join nests" rule.
       DROP TABLE t1,t2,t3,t4,t5;
      

      table t5 has 0 rows, matching_candidates_in_table()=0 and the optimizer decides "Impossible WHERE" ?
      (Before this patch, matching_candidates_in_table() would return 0, but it was not called because the optimizer didn't consider full scan on table t5)

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              Assignee:
              psergei Sergei Petrunia
              Reporter:
              psergei Sergei Petrunia
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                Created:
                Updated:

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