Uncaught exception thrown in session handler.

PDOException: SQLSTATE[HY000]: General error: 1114 The table 'sessions' is full: INSERT INTO {sessions} (sid, ssid, uid, cache, hostname, session, timestamp) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6); Array ( [:db_insert_placeholder_0] => f8CmNpiCrpNqRHExT-jc9GbBIsWEm5kO-e_yHasceL0 [:db_insert_placeholder_1] => [:db_insert_placeholder_2] => 0 [:db_insert_placeholder_3] => 0 [:db_insert_placeholder_4] => 54.81.232.42 [:db_insert_placeholder_5] => messages|a:1:{s:5:"error";a:1:{i:0;s:310:"<em class="placeholder">Warning</em>: file_put_contents(): Only 0 of 17579 bytes written, possibly out of free disk space in <em class="placeholder">boost_write_file()</em> (line <em class="placeholder">1323</em> of <em class="placeholder">/var/www/ensreg_d7/sites/all/modules/contrib/boost/boost.module</em>).";}} [:db_insert_placeholder_6] => 1472513740 ) in _drupal_session_write() (line 209 of /var/www/ensreg_d7/includes/session.inc).