An assertion is an expression that must return a Boolean (true if the
assertion succeeds, false otherwise).
It always relies on metric values, operators, units,
functions, and variables and must be written in the tests
section of the .blackfire.yaml file.
'All pages are fast':
- 'main.wall_time < 50ms'
- 'main.peak_memory < 10mb * var(memory_coeff)'
- 'main.network_out < 10kb'
'Not too many SQL queries on the homepage':
- 'metrics.sql.queries.count < 5'
In the above example, main.network_out, metrics.sql.queries.count, and
main.peak_memory are metric values. 10mb uses a unit to make
the expression more readable, and var(memory_coeff) refers to a
variable for which the value has been defined in the environment.
Blackfire exposes metrics that are associated with the current
profile. The value of one dimension of a metric can be used in assertions;
for instance, the count value of the sql.queries metric is stored in
Learn more about all built-in metrics exposed
in assertions by default and how to create your own.
The available dimensions for metrics are the following ones:
To make assertions more readable, you can add a unit to numbers. A unit is a
multiplier applied to the raw number associated with it.
The default time unit is the millisecond; when using 10 in an assertion
for a time value, that evaluates to 10 milliseconds. But using a unit (like
ms or s) makes assertions more explicit; 10s is interpreted as 10
The default memory unit is the byte. The following units are also
available: kb, kib, mb, mib, gb, gib.
Blackfire also supports the following generic units: k, ki, m,
mi, g, gi.
The following operators are supported in assertions:
Variables are useful when you configure several Blackfire environments to run performance tests on various machines
hosting the same application. Variables make it possible to use the same
.blackfire.yaml configuration on several servers that
have different purposes (e.g. development, staging, production).
Variables can be defined in the environment configuration and used in an
expression by passing the metric key to the var() function.
Variable values may also use units.
Example: You have configured two different environments in Blackfire:
The same application runs on all servers, but the debug mode increases memory
usage a lot. As such, you cannot set the same maximum value for your
assertions on memory.
Your .blackfire.yaml would look like this when using variables:
"Pages shouldn't use too much memory":
- "main.peak_memory < 10mb * var('memory_coeff')"
Now in both your Integration and Production Blackfire environments,
you have to create the memory_coeff variable:
memory_coeff == 2
memory_coeff == 1
The var() function may also receive a default value as a second
This default value is used whenever the variable is not defined in one of your
"Pages shouldn't use too much memory":
- "main.peak_memory < 10mb * var('memory_coeff', 1)"
The vars.xxx notation, supported in older versions of Blackfire, is now
deprecated. We strongly advise you to migrate your expression to use
the var() function instead.
When an assertion is run from an environment, the is_dev() function returns
false when the environment is configured for production usage.
When using builds, it is possible to compare
one build to another. This is useful when you want to validate a code merge
(e.g. a pull-request) by triggering a build webhook or
a Blackfire Player collection of scenarios.
The comparison is made between the current build and a reference build.
The reference build is determined with the following rules:
If the build is periodic, the reference build
is the last successful build in the same environment.
If the build is triggered by a webhook with Blackfire
CLI, the reference build is identified with the value passed to the
--external-parent-id option, in the blackfire build-trigger command.
Note that --external-id option must be set.
blackfire build-trigger \
--title="Build PR 1234" \
If the build is triggered by a webhook with
cURL, the reference build is identified with the value passed to the
external_parent_id POST parameter.
Note that external_id parameter must be set.
curl -X POST https://blackfire.io/api/v2/builds/env/<ENV-UUID>/webhook \
--user "CLIENT-ID:CLIENT-TOKEN" \
-d "endpoint=http://example.com/" \
-d "title=Build PR 1234" \
If the build is triggered by Blackfire Player, the reference build is identified with
the value passed to the BLACKFIRE_EXTERNAL_PARENT_ID environment variable.
Note that BLACKFIRE_EXTERNAL_ID environment variable must be set.
blackfire-player run \
Comparison can be made within assertion expressions thanks to the percent
and diff functions:
If you want to assert that a metric value does not increase by more than a
given percentage between two builds, use the percent function:
"percent(main.wall_time) < 10%"
You can also test the evolution of a metric value in absolute terms with the
"diff(metrics.sql.queries.count) < 2"
In this example, the assertion checks that the profile from the newer build has
less than 2 additional SQL statements compared to the previous one.