If your system smells trouble, it makes sense to inspect the log to see what is going on. The important point is this: not all log entries are created equal. PostgreSQL has a hierarchy of log entries that ranges from DEBUG messages to PANIC.
To the administrator, the following three error levels are of great importance:
- ERROR
- FATAL
- PANIC
ERROR is used for problems such as syntax errors, permission-related problems, and so on. Your log will always contain error messages. The critical factor is: how often does a certain type of error show up? Producing millions of syntax errors is certainly not the ideal strategy to run a database server.
FATAL is more scary than ERROR; you will see messages such as could not allocate memory for shared memory name or unexpected walreceiver state. In other words, those error messages are already really scary and will tell you that things are going wrong.
Finally...