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  1. MariaDB Server
  2. MDEV-26750

Estimation for filtered rows is far off with JSON_HB histogram

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    Details

    • Type: Bug
    • Status: Closed (View Workflow)
    • Priority: Critical
    • Resolution: Fixed
    • Affects Version/s: N/A
    • Fix Version/s: 10.7.1
    • Component/s: Optimizer
    • Labels:
      None
    • Environment:
      preview-10.7-MDEV-26519-json-histograms c548019b

      Description

      drop table if exists t1;
       
      create table t1 (c char(8)) engine=MyISAM;
       
      insert into t1 values ('1x');
      insert into t1 values ('1x');
      insert into t1 values ('1xx');
      insert into t1 values ('0xx');
      insert into t1 select * from t1;
      insert into t1 select * from t1;
       
      set histogram_type= SINGLE_PREC_HB;
      analyze table t1 persistent for all;
      analyze
      select c from t1 where c > '1';
       
      set histogram_type= DOUBLE_PREC_HB;
      analyze table t1 persistent for all;
      analyze
      select c from t1 where c > '1';
       
      set histogram_type= JSON_HB;
      analyze table t1 persistent for all;
      analyze
      select c from t1 where c > '1';
       
      # Cleanup
      drop table t1;
      

      SINGLE_PREC_HB

      +------+-------------+-------+------+---------------+------+---------+------+------+--------+----------+------------+-------------+
      | id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | r_rows | filtered | r_filtered | Extra       |
      +------+-------------+-------+------+---------------+------+---------+------+------+--------+----------+------------+-------------+
      |    1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL | 16   | 16.00  |    74.90 |      75.00 | Using where |
      +------+-------------+-------+------+---------------+------+---------+------+------+--------+----------+------------+-------------+
      

      DOUBLE_PREC_HB

      +------+-------------+-------+------+---------------+------+---------+------+------+--------+----------+------------+-------------+
      | id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | r_rows | filtered | r_filtered | Extra       |
      +------+-------------+-------+------+---------------+------+---------+------+------+--------+----------+------------+-------------+
      |    1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL | 16   | 16.00  |    75.00 |      75.00 | Using where |
      +------+-------------+-------+------+---------------+------+---------+------+------+--------+----------+------------+-------------+
      

      JSON_HB

      +------+-------------+-------+------+---------------+------+---------+------+------+--------+----------+------------+-------------+
      | id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | r_rows | filtered | r_filtered | Extra       |
      +------+-------------+-------+------+---------------+------+---------+------+------+--------+----------+------------+-------------+
      |    1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL | 16   | 16.00  |    33.33 |      75.00 | Using where |
      +------+-------------+-------+------+---------------+------+---------+------+------+--------+----------+------------+-------------+
      

      Results from preview-10.7-MDEV-26519-json-histograms c548019b

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              Assignee:
              psergei Sergei Petrunia
              Reporter:
              elenst Elena Stepanova
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                Created:
                Updated:
                Resolved:

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