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  1. MariaDB Server
  2. MDEV-6191

row_search_for_mysql comment and code consistency about isolation level and gap locks

Details

    • Bug
    • Status: Closed (View Workflow)
    • Minor
    • Resolution: Fixed
    • 5.5.37
    • 5.5.39
    • None
    • None

    Description

      mariadb-5.5/storage/xtradb/row/row0sel.c line 4137

          if (set_also_gap_locks
      		 
              && !(srv_locks_unsafe_for_binlog
      		 
             || trx->isolation_level <= TRX_ISO_READ_COMMITTED)
      		 
              && prebuilt->select_lock_type != LOCK_NONE) {
      		 
       
      		 
            /* Try to place a lock on the index record */
      		 
       
      		 
            /* If innodb_locks_unsafe_for_binlog option is used
      		 
            or this session is using a READ COMMITTED isolation
      		 
            level we do not lock gaps. Supremum record is really
      		 
            a gap and therefore we do not set locks there. */

      I was getting really confused about the comment and its relation to the code and I've come to the conclusion that the comment should say "this session is not using a REPEATABLE READ" and perhaps the condition could be isolation_level < TRX_ISO_REPEATABLE_READ to match.

      Of course I've looked at this too long and just may be wrong.

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          elenst Elena Stepanova added a comment -

          The comment looks okay to me... I mean, for total accuracy, it could have said "using a READ (UN)COMMITTED isolation level", but this "UN" is kind of obvious.
          Although, I've looked at it too briefly, will assign to Jan for an expert look.

          elenst Elena Stepanova added a comment - The comment looks okay to me... I mean, for total accuracy, it could have said "using a READ (UN)COMMITTED isolation level", but this "UN" is kind of obvious. Although, I've looked at it too briefly, will assign to Jan for an expert look.
          jplindst Jan Lindström (Inactive) added a comment -

          Idea with that code is that if innodb_locks_unsafe_for_binlog option is used or this session is using
          READ_COMMITTED or lower isolation level we do not lock gaps. Supremum record is really a
          gap and therefore we do not set locks there.

          jplindst Jan Lindström (Inactive) added a comment - Idea with that code is that if innodb_locks_unsafe_for_binlog option is used or this session is using READ_COMMITTED or lower isolation level we do not lock gaps. Supremum record is really a gap and therefore we do not set locks there.
          jplindst Jan Lindström (Inactive) added a comment -

          revno: 4223
          committer: Jan Lindström <jplindst@mariadb.org>
          branch nick: 5.5
          timestamp: Fri 2014-07-04 08:42:59 +0300
          message:
          MDEV-6191: row_search_for_mysql comment and code consistency about isolation level
          and gap locks

          jplindst Jan Lindström (Inactive) added a comment - revno: 4223 committer: Jan Lindström <jplindst@mariadb.org> branch nick: 5.5 timestamp: Fri 2014-07-04 08:42:59 +0300 message: MDEV-6191 : row_search_for_mysql comment and code consistency about isolation level and gap locks

          People

            jplindst Jan Lindström (Inactive)
            danblack Daniel Black
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            Dates

              Created:
              Updated:
              Resolved:

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