Slow subscribers statistics

This module ranks subscribers and topics in descending order according to the latency of message transmission

Open module

Open EMQX Dashboard, click on the “Module” on the left.

Then, select the Slow Subscribers Statistics module, and then click Enable

Implementation note

With this feature enabled, EMQX will start measuring message transmission latency. The measurement always starts when a message is received by EMQX, the end of the measurement is configurable. See more details below in configurations.

The per clientid-topic latency measurements are then ranked in the table view.

Configuration description

• threshold

  threshold is the minimum number of milliseconds the latency has to exceed, otherwise not collected for ranking

• top_k_num

  This field determines the upper limit of the number of statistical records in the ranking table

• expire_interval

  expire interval controls the effective time of each ranking record. If the a client-topic has no higher latency inserted for such long time, the record expires. For example if expire interval is 5 minutes, and client1-topic1 had a latency 500ms recorded (ranked top-K) at T1, and for the next 5 minutes, if there is no further measurements greater than 500, the ranking recorded will be deleted shortly after T1+5min

• stats_type

  The ways to calculate the latency are as follows:

  1. whole

     From the time the message arrives at EMQX until the message completes transmission

  2. internal

     From when the message arrives at EMQX until when EMQX starts delivering the message

  3. response

     From the time EMQX starts delivering the message, until the message completes transmission

  Definition of message completion transmission:

  1. QoS0

     When EMQX starts to deliver

  2. QoS1

     When EMQX receives puback from the client

  3. Qos2

     When EMQX receives pubcomp from the client

Note: The open source version is configured in emqx.conf

Slow subscribers record

Under this tab, the subscriber information will be displayed in descending order according to the time latency. After Clicking Client ID, it will display the subscriber details, where you can analyze and find the problem.