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up vote 3 down vote favorite

At my work I was running a complex query. I cancelled it and went home yesterday. This morning in the back the query was impossible to be terminated, also with the 'terminate backend' functionality. A colleague of mine restarted the host machine where postgres is installed. After the machine restart, the postgres database sever would not start up.

In my log files I see the error:

'pg_ctl: this data directory appears to be running a pre-existing postmaster'

I am not sure how to handle this problem. I could try to fix it or try to extrapolate the data from the save files. What is the most logical step to take and do you know how to fix this?

Earlier it gave this error message :

2016-01-28 15:52:33 GMT FATAL: lock file "postmaster.pid" already exists
2016-01-28 15:52:33 GMT HINT: Is another postmaster (PID 2100) running in data directory "C:/PostgreSQL/9.1/data"?

UPDATE... I located the file postmaster.pid and deleted it. Now I am restarting the computer and hoping it will start.

UPDATE... It works now. I rebooted the computer and postgres just instantly started. Happy as a child but at the same time not fully satisfied because of the following forum: http://superuser.com/questions/553045/fatal-lock-file-postmaster-pid-already-exists . Here it is stated to NEVER delete the postmaster.pid because of possible data corruption. So because of that I will backup all databases I have in postgres now.

So if anyone can share some more light on my ICT adventure of today I would be very satisfied. That is why I will not state that this question is answered, since I have no idea what went wrong and perhaps will run into it again someday.

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up vote 2 down vote accepted

The explanation is pretty straightforward. PostgreSQL writes the process ID to a file called postmaster.pid — the presence of the file is supposed to indicate that the server is running. When the PostgreSQL shuts down cleanly, it removes the postmaster.pid file.

However, when your colleague restarted the host machine, the PostgreSQL server got killed without having had a chance to remove the postmaster.pid file. Therefore, when you tried to start PostgreSQL, the presence of the file made it look complain that the server was already running.

This answer provides more complete advice. In general, you should never delete postmaster.pid for no good reason, because it's supposed to help prevent two servers from running at once on the same data files. However, if you are certain that the process indicated by the postmaster.pid file is already dead, then by all means just delete the stale PID file manually.

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up vote -2 down vote

In windows Delete all running postgres processes and start the service

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