Inspecting the log
If your system is in 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 equally. PostgreSQL has a hierarchy of log entries that range from DEBUG to PANIC.
For the administrator, the following three error levels are of great importance:
ERRORFATALPANIC
ERROR is used for problems such as syntax errors, permission-related problems, and more. Your log will always contain error messages. The critical factor is this—how often does a certain type of error show up? Producing millions of syntax errors is certainly not an ideal strategy for running a database server.
FATAL is scarier than ERROR; you will see messages such as could not allocate memory for shared memory name or unexpected walreceiver state. In other words, these error messages are already really scary and will tell you that things are going wrong.
Finally, there is PANIC. If you come across...
