interval vs flush_interval in telegraf

Question

I have a following telegraf configuration

[agent]
  interval = "5s"
  round_interval = true
  metric_batch_size = 1000
  metric_buffer_limit = 10000
  collection_jitter = "0s"
  flush_interval = "5s"
  flush_jitter = "0s"
  precision = ""
  debug = false
  quiet = false
  logfile = ""
  hostname = "$HOSTNAME"
  omit_hostname = false

[[outputs.influxdb]]
  urls = ["http://influxdb:8086"]
  database = "telegraf"
  username = ""
  password = ""
  retention_policy = ""
  write_consistency = "any"
  timeout = "5s"

[[inputs.docker]]
  endpoint = "unix:///var/run/docker.sock"
  container_names = []
  timeout = "5s"
  perdevice = true
  total = false

[[inputs.cpu]]
[[inputs.system]]
[[inputs.influxdb]]
  urls = ["http://influxdb:8086/debug/vars"]
[[inputs.syslog]]
#   ## Specify an ip or hostname with port - eg., tcp://localhost:6514, tcp://10.0.0.1:6514
#   ## Protocol, address and port to host the syslog receiver.
#   ## If no host is specified, then localhost is used.
#   ## If no port is specified, 6514 is used (RFC5425#section-4.1).
  server = "tcp://localhost:6514"

[[inputs.socket_listener]]
# ## URL to listen on
service_address = "udp4://:8094"
data_format = "influx"

I need to dump data as fast as possible to my influx DB. I understand that it has something to do with interval and flush_interval settings (here is what I've been reading), but I can't figure out what is the difference between interval and flush_interval. Would someone be able to help me out?

Answer 1

I've asked the maintainer of Telegraf to provide an answer to this question. Here it is:

You can think of inputs as falling into 2 categories: polling (regular) and event driven (service inputs). The interval is the frequency that polling inputs plugins look for data. Most of the event driven plugins do not use the interval, although the statsd plugin is a notable exception.

All collected data has a timestamp, this means that regardless of how long it takes to send the data, it will have the timestamp of when it was sampled.

The flush_interval is how frequently the outputs write data. This is the longest you will have to wait under normal circumstances for the data to be written. The metric_batch_size setting also comes into play here, if this number of new metrics are collected then the output will immediately flush. In other words, Telegraf will trigger a write when either metric_batch_size new metrics are collected or after flush_interval, whichever comes first.