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  1. MariaDB Server
  2. MDEV-22383

Use Block Nested Loops Hash Join by default when appropriate

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    • Task
    • Status: Stalled (View Workflow)
    • Major
    • Resolution: Unresolved
    • None
    • Optimizer
    • None

    Description

      Currently joining a table by Block Nested Loops Hash (BNLH) algorithm is not considered as an option by default. Usage of this algorithm is enabled only when the system variable join_cache_level is set to a value greater than 3. Now by default this variable is set to 2.

      The goals of this task are:
      1. To enable usage of BNLH joins by default.
      2. To use BNLH when joined table has no matching index for key access.
      3. To provide cost-based solution for the choice between BNLH and BKA/NLJ algorithms when joining a table.
      4. To support usage of BNLH for equi-join conditions of the form f1(t1.a)=f2(t2.b)

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          relates to

          Bug - A problem which impairs or prevents the functions of the product. MDEV-16337 Setting join_cache_level=4 changes efficient ref access plan to an inefficient hash join

          • Major - Major loss of function.
          • Open

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              igor Igor Babaev
              igor Igor Babaev
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              Dates

                Created:
                Updated:

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