Check MySQL updating

In most cases, this step make be skipped. You may want to return to this step, if the next one fails (e.g. no rrdtool update to be found)

From debug log, please find the MySQL update statement for that host concerning table poller_output. On very rare occasions, this will fail. So please copy that sql statement and paste it to a mysql session started from cli. This may as well be done from some tool like phpMyAdmin. Check the sql return code.