For complete changes, please refer
http://dev.mysql.com/doc/refman/5.0/en/releasenotes-cs-5-0-67.html.
Here is a part of it.
Functionality added or changed:
Security Enhancement:
To enable stricter control over the location from which user-defined
functions can be loaded, the plugin_dir system variable has been
backported from MySQL 5.1. If the value is non-empty, user-defined
function object files can be loaded only from the directory named by this
variable. If the value is empty, the behavior that is used before 5.0.67
applies: The UDF object files must be located in a directory that is
searched by your system's dynamic linker. (Bug#37428)
Important Change: Incompatible Change:
The FEDERATED storage engine is now disabled by default in the .cnf files
shipped with MySQL distributions (my-huge.cnf, my-medium.cnf, and so
forth). This affects server behavior only if you install one of these
files. (Bug#37069)
Cluster API: Important Change:
Because NDB_LE_MemoryUsage.page_size_kb shows memory page sizes in bytes
rather than kilobytes, it has been renamed to page_size_bytes. The name
page_size_kb is now deprecated and thus subject to removal in a future
release, although it currently remains supported for reasons of backward
compatibility. See The Ndb_logevent_type Type, for more information about
NDB_LE_MemoryUsage. (Bug#30271)
Important Change:
Some changes were made to CHECK TABLE ... FOR UPGRADE and REPAIR TABLE
with respect to detection and handling of tables with incompatible .frm
files (files created with a different version of the MySQL server). These
changes also affect mysqlcheck because that program uses CHECK TABLE and
REPAIR table, and thus also mysql_upgrade because that program invokes
mysqlcheck.
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