Throttle Filter

The Throttle Filter plugin sets the average Rate of messages per Interval, based on leaky bucket and sliding window algorithm. In case of overflood, it will leak within certain rate.

Configuration Parameters

The plugin supports the following configuration parameters:

Key Value Format Description
Rate Integer Amount of meassages for the time.
Window Integer Amount of intervals to calculate average over. Default 5.
Interval String Time interval, expressed in "sleep" format. e.g 3s, 1.5m, 0.5h etc
Print_Status Bool Whether to print status messages with current rate and the limits to information logs

Functional description

Lets imagine we have configured:

Rate 5
Window 5
Interval 1s

we received 1 message first second, 3 messages 2nd, and 5 3rd. As you can see, disregard that Window is actually 5, we use "slow" start to prevent overflooding during the startup.

+-------+-+-+-+ 
|1|3|5| | | | | 
+-------+-+-+-+ 
|  3  |         average = 3, and not 1.8 if you calculate 0 for last 2 panes. 
+-----+

But as soon as we reached Window size * Interval, we will have true sliding window with aggregation over complete window.

+-------------+ 
|1|3|5|7|3|4| | 
+-------------+ 
  |  4.4    |   
  ----------+

When we have average over window is more than Rate, we will start dropping messages, so that

+-------------+
|1|3|5|7|3|4|7|
+-------------+
    |   5.2   |
    +---------+

will become:

+-------------+
|1|3|5|7|3|4|6|
+-------------+
    |   5     |
    +---------+

As you can see, last pane of the window was overwritten and 1 message was dropped.

Interval vs Window size

You might noticed possibility to configure Interval of the Window shift. It is counter intuitive, but there is a difference between two examples above:

Rate 60
Window 5
Interval 1m

and

Rate 1
Window 300
Interval 1s

Even though both examples will allow maximum Rate of 60 messages per minute, first example may get all 60 messages within first second, and will drop all the rest for the entire minute:

XX        XX        XX
XX        XX        XX
XX        XX        XX
XX        XX        XX
XX        XX        XX
XX        XX        XX
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

While the second example will not allow more than 1 message per second every second, making output rate more smooth:

  X    X     X    X    X    X
XXXX XXXX  XXXX XXXX XXXX XXXX
+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+

It may drop some data if the rate is ragged. I would recommend to use bigger interval and rate for streams of rare but important events, while keep Window bigger and Interval small for contantly intensive inputs.

Command Line

Note: It's suggested to use a configuration file.

The following command will load the tail plugin and read the content of lines.txt file. Then the throttle filter will apply a rate limit and only pass the records which are read below the certain rate:

$ bin/fluent-bit -i tail -p 'path=lines.txt' -F throttle -p 'rate=1' -m '*' -o stdout

Configuration File

[INPUT]
    Name   tail
    Path   lines.txt

[FILTER]
    Name     throttle
    Match    *
    Rate     1000
    Window   300
    Interval 1s

[OUTPUT]
    Name   stdout
    Match  *

The example above will pass 1000 messages per second in average over 300 seconds.

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