I have a large Drupal 7 site with many concurrent logged-in users running on a server where disk space recently ran out (MySQL InnoDB behind Memcached on Ubuntu 16.04). How/why this happened is a discussion for another day.
I've cleared up the disk space issue, and the site seems to be running fine as far as general interaction indicates, but Drupal log is full of errors like this:
Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 3 Error writing file '/tmp/MYGWmIvU' (Errcode: 28 - No space left on device)' in /var/www/pixelscrapper.com/public_html/includes/database/database.inc:2229
My question now is: will the mysql database that is running Drupal likely be corrupted/flaky at this point? i.e. On a scale of 0-10, how vital is it that I restore the database to a point before the disk space ran out?
(Anything other than 0 means I will likely restore the database--but there are other things that went wrong as well here, which means that we would lose quite a few days of data if I need to restore, which is a huge drag. C'est la vie, etc.).
My assumption is that the data in MySQL may be more or less fine, but that I cannot rely on the integrity of the actual Drupal data (users, nodes, etc.) which are made up of collections of many database rows...
Out of space crashes can cause serious damages to databases. The sole fact that your database is able to startup and to run apparently as usual is already a good indication that it was not totally messed up by the incident.
Next thing you can do is to perform an in-depth scan using the sqlcheck program :
The mysqlcheck client performs table maintenance: It checks, repairs, optimizes, or analyzes tables.
Analyze all tables in all databases :
$ mysqlcheck -A
Analyze and repair all tables in all databases :
$ mysqlcheck -A -r
NB : as explained in the documentation, you would better shutdown your application and make a backup before you run this.