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  1. MariaDB Server
  2. MDEV-30803

ANALYZE FORMAT=JSON, Join buffer: loops is in wrong position

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Details

    • Bug
    • Status: Open (View Workflow)
    • Major
    • Resolution: Unresolved
    • 11.0(EOL)
    • 11.0(EOL)
    • Optimizer
    • None

    Description

      Check out this example:

      create table t1 (a int);
      insert into t1 select seq from seq_1_to_10;
       
      create table t2 (a int);
      insert into t2 select seq from seq_1_to_10;
       
      analyze format=json 
      select * 
      from t1, t2
      where t1.a=t2.a;
      

      Shows

      ...
            {
              "block-nl-join": {
                "table": {
                  "table_name": "t2",
                  "access_type": "all",
                  "loops": 10,
                  "r_loops": 1,
                  "rows": 10,
                  "r_rows": 10,
                  "cost": 0.02238006,
                  "r_table_time_ms": 0.060573394,
                  "r_other_time_ms": 0.00925612,
                  "filtered": 100,
                  "r_filtered": 100
                },
                "buffer_type": "flat",
                "buffer_size": "65",
                "join_type": "BNL",
                "attached_condition": "t2.a = t1.a",
                "r_filtered": 10,
                "r_unpack_time_ms": 0.004839758
              }
      

      This part looks very misleading:

                "table": {
                  "table_name": "t2",
                  "access_type": "all",
                  "loops": 10,
                  "r_loops": 1,
      

      We do not expect table t2 to be read 10 times.
      "loops" should outside of table object, in block-nl-join.

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            psergei Sergei Petrunia
            psergei Sergei Petrunia
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            Dates

              Created:
              Updated:

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