After updating to UUID 7.x-1.0-alpha5, I get this when running drush cc all:

PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: DELETE FROM {semaphore} WHERE (value = :db_condition_placeholder_0);
Array (
[:db_condition_placeholder_0] => 154951884751e0c13d5589f3.21783230
)
in lock_release_all() (line 269 of /www/includes/lock.inc).
PHP Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 2006 MySQL server has gone away' in /www/includes/database/database.inc:2139
Stack trace:
#0 /www/includes/database/database.inc(2139): PDOStatement->execute(Array)
#1 /www/includes/database/database.inc(664): DatabaseStatementBase->execute(Array, Array)
#2 /www/includes/database/database.inc(2318): DatabaseConnection->query('SELECT expire, ...', Array, Array)
#3 /www/includes/lock.inc(167): db_query('SELECT expire, ...', Array)
#4 /www/includes/lock.inc(146): lock_may_be_available('schema:runtime:...')
#5 /www/includes/bootstrap.inc(420): lock_acquire('schema:runtime:...')
#6 /www/includes/bootstrap.inc(442): Drupal in /www/includes/database/database.inc on line 2139

Can't get any pages to load or drush to do anything, have to restore previous copy of db and rollback the code to previous version.