flush_mode interval flush_interval 1s didn't flush but flush_at_shutdown true did

[jayenashar]

i'm not sure if i've misconfigured fluentd or what, but sometimes the buffer gets stuck and doesn't flush no matter how many times i restart fluentd. i did manage to flush it with flush_at_shutdown true but i don't understand why sometimes flush_mode interval flush_interval 1s doesn't work.

it always logs [debug]: #0 flush_thread actually running when starting fluentd (once for each thread)

here's my buffer config:

  <buffer>
    flush_interval 1s
    flush_mode interval
    retry_type periodic
    @type file
    path /home/jayenashar/fluentd/log/fluentd.buffer
    flush_thread_count 2
    overflow_action block
  </buffer>

and the log when it did flush:

2022-10-03 08:33:07 +0000 [trace]: #0 trying flush for a chunk chunk="5ecadf72da87ef15d793b80f975b8be3"
2022-10-03 08:33:07 +0000 [trace]: #0 adding write count instance=33580
2022-10-03 08:33:07 +0000 [trace]: #0 executing sync write chunk="5ecadf72da87ef15d793b80f975b8be3"
2022-10-03 08:33:07 +0000 [warn]: #0 Dropping log entries with malformed record: 'nil' from tag '0' at ''. A log record should be in JSON format.
2022-10-03 08:33:07 +0000 [debug]: #0 calling logging.googleapis.com:443:/google.logging.v2.LoggingServiceV2/WriteLogEntries