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  1. MariaDB Server
  2. MDEV-21296

Data corruption after DROP COLUMN on InnoDB tables with char primary key

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    Details

    • Type: Bug
    • Status: Closed (View Workflow)
    • Priority: Critical
    • Resolution: Duplicate
    • Affects Version/s: 10.4.10
    • Fix Version/s: N/A
    • Labels:
      None
    • Environment:
      10.4.10-MariaDB-log - mariadb.org binary distribution on Windows 10 (1909)

      Description

      When an InnoDB table has a char field with a UTF8 collation which is set as primary key, dropping a column seems to cause data corruption.

      The problem can be reproduced on a fresh database by executing the following queries:

      CREATE TABLE example (
        id char(8) COLLATE utf8mb4_bin NOT NULL,
        extra_column int NOT NULL,
        PRIMARY KEY (id)
      ) ENGINE=InnoDB;
       
      ALTER TABLE example DROP COLUMN extra_column;
      

      The altered table keeps working fine until the MariaDB server is restarted. But after restart, attempts to access the table result in the following error:

      #1932 - Table 'test.example' doesn't exist in engine

      mysql_error.log excerpt:

      2019-12-12 1:19:55 25 [ERROR] InnoDB: Table `test`.`example` contains unrecognizable instant ALTER metadata

      The problem seems to occur only if the data type of the primary key column is char and only for certain collations (utf8mb4_bin, utf8_bin, utf8_unicode_ci, ...), but for any lengths. The data type of the column that is dropped does not seem to matter.

      I presume this bug is related to the alter algorithm: It occurs with DEFAULT, INPLACE, NOCOPY and INSTANT, but not with COPY, i.e., the problem can be avoided by executing

      SET SESSION alter_algorithm='COPY';
      

      before running the ALTER query. If the table has already been altered but the MariaDB server has not yet been restarted, recreating the table via

      OPTIMIZE TABLE example;
      

      seems to prevent the mentioned data corruption.

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              Assignee:
              Unassigned
              Reporter:
              leibi Dominik Leibenger
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                Dates

                Created:
                Updated:
                Resolved: