Specifies how the timestamp is to be assigned for each line:
Sets the timestamp to the time the first point was logged.
Sets the timestamp to the time the last point was logged. This is the recommended choice.
Sets the timestamp to the average log time of all the points.
An optional log or group label.
The timestamp command lets you set the time resolution for each line. If no label is specified, this command sets a global default value for all logs and groups. Any specific value always overrides the global definition, regardless of the order in the configuration file or when a command is sent.
We recommend setting the timestamp to last, so the lines of output will be written in a non-decreasing order. Of course, this will only be true if the data itself is ordered incrementally by times. Otherwise, you may have to post-process the file and sort it to create a non-decreasing time sequence.