mysqld: dict0dict.ic:879: dict_field_t* dict_index_get_nth_field(const dict_index_t*, ulint): Assertion `pos < index->n_def' failed.

Problem hit during RQG testing on

10.4.7 commit 5a95a33e309d0b2c6bc0f938ad925e3f74b0f921 2019-07-18

compiled with debug.

No replay on actual 10.3.

Version: '10.4.7-MariaDB-debug-log'  ...

mysqld: /work/10.4/storage/innobase/include/dict0dict.ic:879: dict_field_t* dict_index_get_nth_field(const dict_index_t*, ulint): Assertion `pos < index->n_def' failed.

mysqld: /work/10.4/storage/innobase/include/dict0dict.ic:879: dict_field_t* dict_index_get_nth_field(const dict_index_t*, ulint): Assertion `pos < index->n_def' failed.

190718 13:19:53 [ERROR] mysqld got signal 6 ;

Some IMHO important characteristics of that problem

- neither FOREIGN KEYs nor FULLTEXT indexes nor virtual columns nor blobs are involved

- certain InnoDB system variables which are known to cause sometimes trouble are switched to "harmless" values

- only three concurrent sessions/threads are involved

Simplified RQG grammar MDEV-20090.yy (just for illustration, please use the uploaded file when trying to replay).

thread1:

    INSERT INTO t1 (col1, col_int) VALUES ( 4 , 4); ROLLBACK ;

thread1_connect:

     ;

thread1_init:

    CREATE TABLE IF NOT EXISTS t1 ( col1 INT PRIMARY KEY, col_int INTEGER ) ENGINE = InnoDB ROW_FORMAT = Dynamic ;

thread2:

    DELETE FROM t1 WHERE col1 = 4 OR col1 IS NULL ; COMMIT ;

thread2_connect:

     ;

thread2_init:

     ;

thread3:

    ALTER TABLE t1 ADD UNIQUE INDEX `uidx3` ( col_int ) , ALGORITHM = NOCOPY , LOCK = NONE |

    ALTER TABLE t1 ADD UNIQUE INDEX `uidx3` ( col_int ) , ALGORITHM = NOCOPY , LOCK = NONE |

    ALTER TABLE t1 ADD UNIQUE INDEX `uidx3` ( col_int ) , ALGORITHM = NOCOPY , LOCK = NONE |

    ALTER TABLE t1 ADD UNIQUE INDEX `uidx3` ( col_int ) , ALGORITHM = NOCOPY , LOCK = NONE |

    ALTER TABLE t1 ADD COLUMN col_int_copy INTEGER FIRST , ALGORITHM = NOCOPY , LOCK = NONE ; ALTER TABLE t1 DROP COLUMN IF EXISTS col_int , ALGORITHM = NOCOPY , LOCK = NONE ; ALTER TABLE t1 CHANGE COLUMN IF EXISTS col_int_copy col_int INTEGER , ALGORITHM = NOCOPY , LOCK = NONE ;

thread3_connect:

     ;

thread3_init:

     ;