If you upgrade to MySQL 4.1.1 or higher, it is difficult to
downgrade back to 4.0 or 4.1.0. That is because, for earlier
InnoDB is not aware of multiple
New binary log format that enables replication of these session
foreign_key_checks (which was
replicated since 4.0.14, but here it is done more efficiently
and takes less space in the binary logs),
unique_checks. Other variables
(like character sets,
sql_select_limit, ...) will be
replicated in upcoming 5.0.x releases.
Replication: Easier replication upgrade (5.0.0 masters can read older binary logs and 5.0.0 slaves can read older relay logs). See Replication Compatibility Between MySQL Versions, for more details). The format of the binary log and relay log is changed compared to that of MySQL 4.1 and older.
The output of the
EVENTS statement has been modified. The
Orig_log_pos column has been renamed to
End_log_pos and now represents the offset of
the last byte of the event, plus one.
KILL statement now takes
modifiers. The first is the same as
KILL with no modifier (it kills a
given connection thread). The second kills only the statement
currently being executed by the connection.
For user-defined functions (UDFs), the
UDF_ARGS structure now has
attribute_lengths members that provide
information about the argument names.
UDF Argument Processing.
The precedence of the
XOR operator now lies
XOR had the same precedence as
Basic support for stored procedures and functions (SQL:2003 style). See Using Stored Routines (Procedures and Functions).
INFILE causes an implicit commit.
The behavior of
INFILE in this regard was changed again in MySQL
5.0.26. See the section called “Changes in MySQL 5.0.26 (2006-10-03)”.
Implemented Index Merge optimization for
clauses. See Index Merge Optimization.