• unknown's avatar
    Bug#19025 4.1 mysqldump doesn't correctly dump "auto_increment = [int]" · d300ceea
    unknown authored
    mysqldump / SHOW CREATE TABLE will show the NEXT available value for
    the PK, rather than the *first* one that was available (that named in
    the original CREATE TABLE ... AUTO_INCREMENT = ... statement).
    
    This should produce correct and robust behaviour for the obvious use
    cases -- when no data were inserted, then we'll produce a statement
    featuring the same value the original CREATE TABLE had; if we dump
    with values, INSERTing the values on the target machine should set the
    correct next_ID anyway (and if not, we'll still have our AUTO_INCREMENT =
    ... to do that). Lastly, just the CREATE statement (with no data) for
    a table that saw inserts would still result in a table that new values
    could safely be inserted to).
    
    There seems to be no robust way however to see whether the next_ID
    field is > 1 because it was set to something else with CREATE TABLE
    ... AUTO_INCREMENT = ..., or because there is an AUTO_INCREMENT column
    in  the table (but no initial value was set with AUTO_INCREMENT = ...)
    and then one or more rows were INSERTed, counting up next_ID. This
    means that in both cases, we'll generate an AUTO_INCREMENT =
    ... clause in SHOW CREATE TABLE / mysqldump.  As we also show info on,
    say, charsets even if the user did not explicitly give that info in
    their own CREATE TABLE, this shouldn't be an issue.
    
    As per above, the next_ID will be affected by any INSERTs that have
    taken place, though.  This /should/ result in correct and robust
    behaviour, but it may look non-intuitive to some users if they CREATE
    TABLE ... AUTO_INCREMENT = 1000 and later (after some INSERTs) have
    SHOW CREATE TABLE give them a different value (say, CREATE TABLE
    ... AUTO_INCREMENT = 1006), so the docs should possibly feature a
    caveat to that effect.
    
    It's not very intuitive the way it works now (with the fix), but it's
    *correct*.  We're not storing the original value anyway, if we wanted
    that, we'd have to change on-disk representation?
    
    If we do dump/load cycles with empty DBs, nothing will change.  This
    changeset includes an additional test case that proves that tables
    with rows will create the same next_ID for AUTO_INCREMENT = ... across
    dump/restore cycles.
    
    Confirmed by support as likely solution for client's problem.
    
    
    mysql-test/r/auto_increment.result:
      test for creation of AUTO_INCREMENT=... clause
    mysql-test/r/gis-rtree.result:
      Add AUTO_INCREMENT=... clauses where appropriate
    mysql-test/r/mysqldump.result:
      show that AUTO_INCREMENT=... will survive dump/restore cycles
    mysql-test/r/symlink.result:
      Add AUTO_INCREMENT=... clauses where appropriate
    mysql-test/t/auto_increment.test:
      test for creation of AUTO_INCREMENT=... clause
    mysql-test/t/mysqldump.test:
      show that AUTO_INCREMENT=... will survive dump/restore cycles
    sql/sql_show.cc:
      Add AUTO_INCREMENT=... to output of SHOW CREATE TABLE if there is an
      AUTO_INCREMENT column, and NEXT_ID > 1 (the default).  We must not print
      the clause for engines that do not support this as it would break the
      import of dumps, but as of this writing, the test for whether
      AUTO_INCREMENT columns are allowed and wether AUTO_INCREMENT=...
      is supported is identical, !(file->table_flags() & HA_NO_AUTO_INCREMENT))
      Because of that, we do not explicitly test for the feature,
      but may extrapolate its existence from that of an AUTO_INCREMENT column.
    d300ceea
gis-rtree.result 45.2 KB