Some of the connections between my application server (Ubuntu, Apache, PHP) and my DB server (Ubuntu, MySQL) are failing with error code 4. According to the documentation error code 4 is:
OS error code 4: Interrupted system call
At first I thought that maybe the issue is that the DB server has too many connections and fails because there are too much open files. But it seems not to be the case because:
- Too many open files has different error code (24).
- I've checked and during peak time the server had 497 files open (checked using lsof command) while the maximum is 1024.
The TCP settings were already checked (see prior question).
Any ideas what this can be or what should I check?