The ReliableSpoolingFileEventReader reads the oldest file in the spooling directory first. This is done by listing the directory contents and then sorting file list based on timestamp. This may be very slow if there are a lot of files (of the order of 100K or more) in the directory.
However, this is not always needed, there can be simple cases in which the order to consume the file is not important.
There should be an option of consuming the files in arbitrary order, allowing the files to be consumed quickly without any delay.