basho/lager — pull request #120 by Vagabond (2013-03-14 20:10:51+00:00)
Title: Improve the performance of the file backend

This is done via a combination of several things:
* Make the loglevel that triggers a sync configurable
* Make the delayed_write size and intervals configurable
* Make the interval at which external rotation is checked for
configurable
* Store the timestamp a lager_msg was created inside the lager_msg

To support these changes, several other things had to be modified:
* lager_msg:timestamp now returns a timestamp
* lager_msg:datetime was added to return the {date, time} of a message,
like lager_msg:timestamp used to
* The configuration syntax for file backends was changed to be of the
form {lager_file_backend, proplist()} and the old syntax was
deprecated

Additionally, the defaults for the check_interval was raised from
'always' to 1 second, and the sync_interval was changed from 2 seconds
to one second.