Mysql crashed once a day

Hello,

about 2 ou 4 days, I have some trouble like this:

Roundcube:
DATABASE ERROR: CONNECTION FAILED!
Unable to connect to the database!
Please contact your server-administrator.

When a I do a service status: I see that msql is inactive
The mysql service is stopped or crashed …

/var/log/mysql.err is empty

I restart the service
$ sudo service mysql start
[ ok ] Starting MySQL database server: mysqld . . . . …
[info] Checking for tables which need an upgrade, are corrupt or were
not closed cleanly…

$mysql --version
mysql Ver 14.14 Distrib 5.5.46, for debian-linux-gnu (armv7l) using readline 6.2

I am using Raspbian Wheezy

And then Yunohost is OK

Could you help me?

THX a lot
Jean