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  1. MariaDB Server
  2. MDEV-9319

ALTER from a bigger to a smaller blob type truncates too much data

Details

    Description

      DROP TABLE IF EXISTS t1;
      		 
      CREATE TABLE t1 (a BLOB) ENGINE=MyISAM;
      		 
      INSERT INTO t1 VALUES (REPEAT(0x61,65000));
      		 
      SELECT LENGTH(a) FROM t1;
      		 
      ALTER TABLE t1 MODIFY a TINYBLOB;
      		 
      SELECT LENGTH(a) FROM t1;

      returns 65000 before ALTER:

      +-----------+
      		 
      | LENGTH(a) |
      		 
      +-----------+
      		 
      |     65000 |
      		 
      +-----------+

      and returns 232 after ALTER:

      +-----------+
      		 
      | LENGTH(a) |
      		 
      +-----------+
      		 
      |       232 |
      		 
      +-----------+

      This looks wrong. The expected length after ALTER is 255.

      It also does not produce any warnings on truncation. Probably it should.

      Attachments

        Issue Links

          blocks

          Epic - Created by Jira Software - do not edit or delete. Issue type for a big user story that needs to be broken down. MDEV-4912 Data type plugin API version 1

          • Minor - Minor loss of function, or other problem where easy workaround is present.
          • Closed
          relates to

          Bug - A problem which impairs or prevents the functions of the product. MDEV-13530 VARBINARY doesn't convert to to BLOB for sizes 65533, 65534 and 65535

          • Major - Major loss of function.
          • Closed

          Activity

            Ascending order - Click to sort in descending order
            bar Alexander Barkov created issue -
            bar Alexander Barkov made changes -
            Field Original Value New Value
            Summary ALTER for a bigger to a smaller blob type truncates too much data ALTER from a bigger to a smaller blob type truncates too much data
            bar Alexander Barkov made changes -
            Description {code}
            DROP TABLE IF EXISTS t1;
            CREATE TABLE t1 (a BLOB) ENGINE=MyISAM;
            INSERT INTO t1 VALUES (REPEAT(0x61,65000));
            SELECT LENGTH(a) FROM t1;
            ALTER TABLE t1 MODIFY a TINYBLOB;
            SELECT LENGTH(a) FROM t1;
            {code}
            returns 65000 before ALTER:
            {code}
            +-----------+
            | LENGTH(a) |
            +-----------+
            | 65000 |
            +-----------+
            {code}
            and returns 232 after ALTER:
            {code}
            +-----------+
            | LENGTH(a) |
            +-----------+
            | 232 |
            +-----------+
            {code}
            This looks wrong. The expected length is 255.

            		 {code}
            DROP TABLE IF EXISTS t1;
            CREATE TABLE t1 (a BLOB) ENGINE=MyISAM;
            INSERT INTO t1 VALUES (REPEAT(0x61,65000));
            SELECT LENGTH(a) FROM t1;
            ALTER TABLE t1 MODIFY a TINYBLOB;
            SELECT LENGTH(a) FROM t1;
            {code}
            returns 65000 before ALTER:
            {code}
            +-----------+
            | LENGTH(a) |
            +-----------+
            | 65000 |
            +-----------+
            {code}
            and returns 232 after ALTER:
            {code}
            +-----------+
            | LENGTH(a) |
            +-----------+
            | 232 |
            +-----------+
            {code}
            This looks wrong. The expected length after ALTER is 255.
            bar Alexander Barkov made changes -
            bar Alexander Barkov made changes -
            Description {code}
            DROP TABLE IF EXISTS t1;
            CREATE TABLE t1 (a BLOB) ENGINE=MyISAM;
            INSERT INTO t1 VALUES (REPEAT(0x61,65000));
            SELECT LENGTH(a) FROM t1;
            ALTER TABLE t1 MODIFY a TINYBLOB;
            SELECT LENGTH(a) FROM t1;
            {code}
            returns 65000 before ALTER:
            {code}
            +-----------+
            | LENGTH(a) |
            +-----------+
            | 65000 |
            +-----------+
            {code}
            and returns 232 after ALTER:
            {code}
            +-----------+
            | LENGTH(a) |
            +-----------+
            | 232 |
            +-----------+
            {code}
            This looks wrong. The expected length after ALTER is 255.

            		 {code}
            DROP TABLE IF EXISTS t1;
            CREATE TABLE t1 (a BLOB) ENGINE=MyISAM;
            INSERT INTO t1 VALUES (REPEAT(0x61,65000));
            SELECT LENGTH(a) FROM t1;
            ALTER TABLE t1 MODIFY a TINYBLOB;
            SELECT LENGTH(a) FROM t1;
            {code}
            returns 65000 before ALTER:
            {code}
            +-----------+
            | LENGTH(a) |
            +-----------+
            | 65000 |
            +-----------+
            {code}
            and returns 232 after ALTER:
            {code}
            +-----------+
            | LENGTH(a) |
            +-----------+
            | 232 |
            +-----------+
            {code}
            This looks wrong. The expected length after ALTER is 255.

            It also does not produce any warnings on truncation. Probably it should.
            bar Alexander Barkov made changes -
            Labels upstream upstream-5.5
            bar Alexander Barkov made changes -
            Fix Version/s 5.5 [ 15800 ]
            Fix Version/s 10.2 [ 14601 ]
            serg Sergei Golubchik made changes -
            Fix Version/s 10.0 [ 16000 ]
            Fix Version/s 10.1 [ 16100 ]
            serg Sergei Golubchik made changes -
            Component/s Data Definition - Alter Table [ 10114 ]
            Component/s OTHER [ 10125 ]
            bar Alexander Barkov made changes -
            Fix Version/s 5.5.48 [ 21000 ]
            Fix Version/s 10.0.24 [ 21101 ]
            Fix Version/s 10.1.11 [ 21202 ]
            Fix Version/s 10.0 [ 16000 ]
            Fix Version/s 5.5 [ 15800 ]
            Fix Version/s 10.1 [ 16100 ]
            Resolution Fixed [ 1 ]
            Status Open [ 1 ] Closed [ 6 ]
            bar Alexander Barkov made changes -
            serg Sergei Golubchik made changes -
            Workflow MariaDB v3 [ 73316 ] MariaDB v4 [ 149935 ]

            People

              bar Alexander Barkov
              bar Alexander Barkov
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              Dates

                Created:
                Updated:
                Resolved:

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