Unreasonably small size for join_buffer_size

CREATE TABLE t1 (f1 INT) ENGINE=MyISAM;

INSERT INTO t1 VALUES (1),(2);

CREATE TABLE t2 (f2 INT) ENGINE=MyISAM;

INSERT INTO t2 VALUES (2),(3);

CREATE TABLE t3 (f3 INT, f4 INT) ENGINE=MyISAM;

INSERT INTO t3 VALUES (3,3),(4,4);

MariaDB [test]> set optimizer_switch='optimize_join_buffer_size=on';

Query OK, 0 rows affected (0.001 sec)

MariaDB [test]> ANALYZE FORMAT=JSON  SELECT f4 FROM t2, t3 WHERE f3 IN ( 1, 3 );

| {

  "query_block": {

    "select_id": 1,

    "r_loops": 1,

    "r_total_time_ms": 0.2752,

    "table": {

      "table_name": "t2",

      "access_type": "ALL",

      "r_loops": 1,

      "rows": 2,

      "r_rows": 2,

      "r_total_time_ms": 0.019,

      "filtered": 100,

      "r_filtered": 100

    },

    "block-nl-join": {

      "table": {

        "table_name": "t3",

        "access_type": "ALL",

        "r_loops": 1,

        "rows": 2,

        "r_rows": 2,

        "r_total_time_ms": 0.0199,

        "filtered": 100,

        "r_filtered": 50,

        "attached_condition": "t3.f3 in (1,3)"

      },

      "buffer_type": "flat",

      "buffer_size": "1",

      "join_type": "BNL",

      "r_filtered": 100

    }

  }

} |