jmeter-retrier

Overview

This Apache JMeter plugin provides a Post-Processor that retries failed samples.

Motivation

JMeter provides no mechanism to retry failed samplers. Sample errors can be ignored (and the thread continues or starts the next loop) or the thread can be stopped.

Scripts that contain a sequence of user interactions have no easy way to recover from sampler errors, but loops and conditions have to be explicitly built into the scripts.

For example, stress tests may get throttled (e.g. HTTP 429) but the script should continue its flow, however, the throttled request would need to be retried.

Results Representation

Retries are added as sub-results, with the initial, failed attempt as the first sub-result with the original label, and all retries thereafter. All retries are labelled with a suffix ("-retryN" with N enumerating the attempts).

The main result contains:

• Request and response data of the final attempt, so that assertions can be applied,
• Total byte count of all attempts,
• Total response time of all attempts (without pauses),
• Label suffix "-retry" (without number).

Usage

Retry Post-Processor

Simply add a Retry Post-Processor to the Scope of samplers that should be retried.

Retry Conditions:

• Max Number of Retries: Positive number limits the number of retries, negative retries infinitely, zero means no retries (default: 0).
• Response Part: Which part of the sample response to check: Response code, data, headers, message, or none (default: None). If "None" is selected, the sample is retried if the result was unsuccessful.
• Error Pattern: Retry if this regex pattern is contained in the response part selected above (default: empty). If empty, the sample is retried if the result was unsuccessful.

Note that the success or failure of the sample result is determined by the sampler itself only. Assertions are not taken into account as they only run after the Retry Post-Processor.

Delay Settings:

• Pause (milliseconds): How long to pause before retrying the sampler or zero for no pause (default: 0).

• Backoff: How to modify the initial Pause after each retry, in order to slow down to avoid overload.

  Backoff	Meaning	n-th Delay	Delays Example
  None	Constant pause between all retries	Pause • 1	100, 100, 100, 100, 100, 100 ms
  Linear	Pause grows linearly	Pause • n	100, 200, 300, 400, 500, 600 ms
  Polynomial	Pause is multiplied with a polynomial factor	Pause • n2	100, 400, 900, 1600, 2500, 3600 ms
  Exponential	Pause doubles with every retry	Pause • 2n	100, 200, 400, 800, 1600, 3200 ms

  The exponent and base of the "Polynomial" and "Exponential" backoff strategies can be configured via JMeter Property jmeter.retrier.backoffMultiplier (default: 2).

• Jitter Factor (positive decimal): Amount of random variation to add to the pauses (default: 0, i.e. jitter turned off). For example, a value of 0.1 will add up to 10% of the Pause to the calculated delay.

• Respect "Retry-After": Whether to respect an HTTP response header "Retry-After" before retrying (default: False). If a non-zero Pause is defined as well, the greater of the two resulting delays will be applied. For example, if the next pause would be 100 ms but the server sends "Retry-After: 10" the effective delay will be 10 seconds rather than 100 ms.

Assertions

Note that this plugin will not execute other JMeter elements, i.e. Pre-Processors, Timers, Post-Processors and Assertions as part of a retry.

Pre-Processors and Timers will only be executed once, before the initial attempt. Likewise, Post-Processors and Assertions will only be executed once, after the final attempt (or before, in case of Post-Processors that appear before the Retry Post-Processor).

Note, this is due to the way a JMeterThread processes Test Plan elements and this cannot be customised unfortunately.

JMeter Properties

The following properties control the plugin behaviour:

• jmeter.retrier.sampleLabelSuffix: Suffix to append to the retried sample's label (default: "-retry").
• jmeter.retrier.backoffMultiplier: Determines how much the pauses increase with each retry, as a exponent/base for polynomial/exponential backoff (default: 2).

Installation

Via PluginsManager

Under tab "Available Plugins", select "Sample Retrier", then click "Apply Changes and Restart JMeter".

Via Package from JMeter-Plugins.org

Extract the zip package into JMeter's lib directory, then restart JMeter.

Via Manual Download

1. Copy the jmeter-retrier jar file into JMeter's lib/ext directory.
2. Restart JMeter.

Limitations

• Minimum JMeter version 5.0
• Pre-Processors, Timers, other Post-Processors, and Assertions are not executed when retrying, but only once (before the first attempt or after the last)
• Connect Time, Latency and Idle Time are not accumulated