A timeout has occured. if you were establishing a connection, increase Timeout value in ConnectionString. If you were executing a command, increase the CommandTimeout value in ConnectionString or in your NpgsqlCommand object.
This is caused by the query taking too long to run.
Ideally, to fix this you should change the query your calling to be more efficient or add some database indexes so it doesn’t take so long to run. If for some reason you can’t do this, you could increase the CommandTimeout value in the ConnectionString or in your NpgsqlCommand object. To do this in the NpgsqlCommand object, do as below:
NpgsqlCommand myObject = new NpgsqlCommand;
myObject.CommandTimeout = 60; // This changes it to wait 60 seconds before timing out. The default is 30 seconds.
Obviously it’s much better to fix the query so it doesn’t take 60 seconds to run.