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  1. MariaDB Server
  2. MDEV-33795

MariaDB segfault on rowid filter query involving generated column

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      Certain queries involving a generated column will cause the mariadb server process to segfault giving output like below before exiting:

      240329  5:38:20 [ERROR] mysqld got signal 11 ;
      Sorry, we probably made a mistake, and this is a bug.
       
      Your assistance in bug reporting will enable us to fix this for the next release.
      To report this bug, see https://mariadb.com/kb/en/reporting-bugs
       
      We will try our best to scrape up some info that will hopefully help
      diagnose the problem, but since we have already crashed,
      something is definitely wrong and this may fail.
       
      Server version: 11.3.2-MariaDB-1:11.3.2+maria~ubu2204 source revision: 068a6819eb63bcb01fdfa037c9bf3bf63c33ee42
      key_buffer_size=134217728
      read_buffer_size=131072
      max_used_connections=1
      max_threads=153
      thread_count=1
      It is possible that mysqld could use up to
      key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 468073 K  bytes of memory
      Hope that's ok; if not, decrease some variables in the equation.
       
      Thread pointer: 0xffff44000c78
      Attempting backtrace. You can use the following information to find out
      where mysqld died. If you see no messages after this, something went
      terribly wrong...
      

      The schema in question looks like

      CREATE TABLE `testtable` (
        `a_id` int(11) DEFAULT NULL,
        `b_id` int(11) NOT NULL,
        `c_id` varchar(64) DEFAULT NULL,
        `d_bool` tinyint(1) DEFAULT 1,
        `d_bool_gen` tinyint(1) GENERATED ALWAYS AS (if(`d_bool`,1,NULL)),
        UNIQUE KEY `testkey` (`b_id`,`c_id`,`d_bool_gen`),
        KEY `a_key` (`a_id`)
      );
      

      Noting the existence of a unique key constraint involving a generated column. Then a query that looks like

      select * from testtable where b_id = 10 and a_id = 10;
      

      can trigger the fault seen above. Explaining the above query gives the output below which is why I suspect the rowid filter is involved

      +------+-------------+-----------+------------+---------------+---------------+---------+-------+----------+---------------------------------+
      | id   | select_type | table     | type       | possible_keys | key           | key_len | ref   | rows     | Extra                           |
      +------+-------------+-----------+------------+---------------+---------------+---------+-------+----------+---------------------------------+
      |    1 | SIMPLE      | testtable | ref|filter | testkey,a_key | testkey|a_key | 4|5     | const | 202 (0%) | Using where; Using rowid filter |
      +------+-------------+-----------+------------+---------------+---------------+---------+-------+----------+---------------------------------+
      

      To help with reproduction I have found that the following synthetic data is sufficient to trigger the fault

      INSERT INTO testtable (a_id, b_id, c_id, d_bool)
      SELECT MOD(seq, 1000), MOD(seq, 1001), IF(MOD(seq, 3) = 0, NULL, LEFT(MD5(seq), 64)), MOD(seq, 2) FROM seq_1_to_100000;
      INSERT INTO testtable (a_id, b_id, c_id, d_bool)
      SELECT 10, 10, IF(MOD(seq, 3) = 0, NULL, LEFT(MD5(-seq), 64)), MOD(seq, 2) FROM seq_1_to_100;
      INSERT INTO testtable (a_id, b_id, c_id, d_bool) VALUES
      (10, 10, '', 0),
      (10, 10, '', 1);
      

      With that synthetic data in place, repeatedly querying the below query will eventually cause the segfault.

      select * from testtable where b_id = 10 and a_id = 10;
      

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              debarun Debarun Banerjee
              msg555 Mark Gordon
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                Updated:
                Resolved:

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