be3b878443
Previously we'd create a separate Metric instance for every method call that would exceed the method call threshold. This is problematic because it doesn't provide us with information to accurately get the _total_ execution time of a particular method. For example, if the method "Foo#bar" was called 4 times with a runtime of ~10 milliseconds we'd end up with 4 different Metric instances. If we were to then get the average/95th percentile/etc of the timings this would be roughly 10 milliseconds. However, the _actual_ total time spent in this method would be around 40 milliseconds. To solve this problem we now create a single Metric instance per method. This Metric instance contains the _total_ real/CPU time and the call count for every instrumented method.
139 lines
3.8 KiB
Markdown
139 lines
3.8 KiB
Markdown
# Instrumenting Ruby Code
|
|
|
|
GitLab Performance Monitoring allows instrumenting of both methods and custom
|
|
blocks of Ruby code. Method instrumentation is the primary form of
|
|
instrumentation with block-based instrumentation only being used when we want to
|
|
drill down to specific regions of code within a method.
|
|
|
|
## Instrumenting Methods
|
|
|
|
Instrumenting methods is done by using the `Gitlab::Metrics::Instrumentation`
|
|
module. This module offers a few different methods that can be used to
|
|
instrument code:
|
|
|
|
* `instrument_method`: instruments a single class method.
|
|
* `instrument_instance_method`: instruments a single instance method.
|
|
* `instrument_class_hierarchy`: given a Class this method will recursively
|
|
instrument all sub-classes (both class and instance methods).
|
|
* `instrument_methods`: instruments all public and private class methods of a Module.
|
|
* `instrument_instance_methods`: instruments all public and private instance methods of a
|
|
Module.
|
|
|
|
To remove the need for typing the full `Gitlab::Metrics::Instrumentation`
|
|
namespace you can use the `configure` class method. This method simply yields
|
|
the supplied block while passing `Gitlab::Metrics::Instrumentation` as its
|
|
argument. An example:
|
|
|
|
```
|
|
Gitlab::Metrics::Instrumentation.configure do |conf|
|
|
conf.instrument_method(Foo, :bar)
|
|
conf.instrument_method(Foo, :baz)
|
|
end
|
|
```
|
|
|
|
Using this method is in general preferred over directly calling the various
|
|
instrumentation methods.
|
|
|
|
Method instrumentation should be added in the initializer
|
|
`config/initializers/metrics.rb`.
|
|
|
|
### Examples
|
|
|
|
Instrumenting a single method:
|
|
|
|
```
|
|
Gitlab::Metrics::Instrumentation.configure do |conf|
|
|
conf.instrument_method(User, :find_by)
|
|
end
|
|
```
|
|
|
|
Instrumenting an entire class hierarchy:
|
|
|
|
```
|
|
Gitlab::Metrics::Instrumentation.configure do |conf|
|
|
conf.instrument_class_hierarchy(ActiveRecord::Base)
|
|
end
|
|
```
|
|
|
|
Instrumenting all public class methods:
|
|
|
|
```
|
|
Gitlab::Metrics::Instrumentation.configure do |conf|
|
|
conf.instrument_methods(User)
|
|
end
|
|
```
|
|
|
|
### Checking Instrumented Methods
|
|
|
|
The easiest way to check if a method has been instrumented is to check its
|
|
source location. For example:
|
|
|
|
```
|
|
method = Rugged::TagCollection.instance_method(:[])
|
|
|
|
method.source_location
|
|
```
|
|
|
|
If the source location points to `lib/gitlab/metrics/instrumentation.rb` you
|
|
know the method has been instrumented.
|
|
|
|
If you're using Pry you can use the `$` command to display the source code of a
|
|
method (along with its source location), this is easier than running the above
|
|
Ruby code. In case of the above snippet you'd run the following:
|
|
|
|
```
|
|
$ Rugged::TagCollection#[]
|
|
```
|
|
|
|
This will print out something along the lines of:
|
|
|
|
```
|
|
From: /path/to/your/gitlab/lib/gitlab/metrics/instrumentation.rb @ line 148:
|
|
Owner: #<Module:0x0055f0865c6d50>
|
|
Visibility: public
|
|
Number of lines: 21
|
|
|
|
def #{name}(#{args_signature})
|
|
if trans = Gitlab::Metrics::Instrumentation.transaction
|
|
trans.measure_method(#{label.inspect}) { super }
|
|
else
|
|
super
|
|
end
|
|
end
|
|
```
|
|
|
|
## Instrumenting Ruby Blocks
|
|
|
|
Measuring blocks of Ruby code is done by calling `Gitlab::Metrics.measure` and
|
|
passing it a block. For example:
|
|
|
|
```ruby
|
|
Gitlab::Metrics.measure(:foo) do
|
|
...
|
|
end
|
|
```
|
|
|
|
The block is executed and the execution time is stored as a set of fields in the
|
|
currently running transaction. If no transaction is present the block is yielded
|
|
without measuring anything.
|
|
|
|
3 values are measured for a block:
|
|
|
|
1. The real time elapsed, stored in NAME_real_time.
|
|
2. The CPU time elapsed, stored in NAME_cpu_time.
|
|
3. The call count, stored in NAME_call_count.
|
|
|
|
Both the real and CPU timings are measured in milliseconds.
|
|
|
|
Multiple calls to the same block will result in the final values being the sum
|
|
of all individual values. Take this code for example:
|
|
|
|
```ruby
|
|
3.times do
|
|
Gitlab::Metrics.measure(:sleep) do
|
|
sleep 1
|
|
end
|
|
end
|
|
```
|
|
|
|
Here the final value of `sleep_real_time` will be `3`, _not_ `1`.
|