Behaviour of Fluentd's position log file when tailing a consistently changing log file

Hi, I’m new with Fluentd and I’m curious about the behaviour of Fluentd’s position log file when a log file which has been tailed by in_tail is consistently changing.

I know that the position log file has 3 row: 1st one is log file name; 2nd one is FilePositionEntry and 3rd one is MemoryPositionEntry. The idea is like the _consumer_offsets from Kafka. I also know that if the log file is grow up, the log file will update the FilePositionEntry and tell the agent that it still got work to be done.

But here is the case, if I have only one log file which is consistently changing, let’s say from 0 to 20 MB, and as soon as it reaches the last byte of it’s size, it will null-echoed itself to make room for new log entries from the top of the file. Can Fluentd’s position log file detects the change in reduction of log file’s MemoryPositionEntry and what will it do after then? Note that the file can be considered as “rotating” but it won’t make any rotated file rather than clean up itself.

I know this question sounds like a not-so-smart one but it’s my curiousity and also the reason I come here to ask everyone about it. :smiley:
Thanks guy, hope everyone can have a good day and be safe from the pandemic.