---
title: "Tracing"
description: "Learn how to set up and enable tracing in your PHP app and discover valuable performance insights of your application."
url: https://docs.sentry.io/platforms/php/guides/symfony/tracing/
---

# Set Up Tracing in PHP | Sentry for Symfony

With [tracing](https://docs.sentry.io/product/insights/overview.md), Sentry tracks your software performance, measuring metrics like throughput and latency, and displaying the impact of errors across multiple systems. Sentry captures distributed traces consisting of transactions and spans, which measure individual services and individual operations within those services. Learn more about our model in [Distributed Tracing](https://docs.sentry.io/product/sentry-basics/tracing/distributed-tracing.md).

If you’re adopting Tracing in a high-throughput environment, we recommend testing prior to deployment to ensure that your service’s performance characteristics maintain expectations.

## [Configure](https://docs.sentry.io/platforms/php/guides/symfony/tracing.md#configure)

First, enable tracing and configure the sample rate for transactions. Set the sample rate for your transactions by either:

* Setting a uniform sample rate for all transactions using the `traces_sample_rate` option in your SDK config to a number between `0` and `1`. (For example, to send 20% of transactions, set `traces_sample_rate` to `0.2`.)
* Controlling the sample rate based on the transaction itself and the context in which it's captured, by providing a function to the `traces_sampler` config option.

The two options are meant to be mutually exclusive. If you set both, `traces_sampler` will take precedence.

`config/packages/sentry.yaml`

```yaml
sentry:
  options:
    # Specify a fixed sample rate:
    traces_sample_rate: 1.0
    # Or provide a custom sampler:
    traces_sampler: "sentry.callback.traces_sampler"

# Only needed when using the `traces_sampler`
services:
  sentry.callback.traces_sampler:
    class: 'App\Service\Sentry'
    factory: ['@App\Service\Sentry', "getTracesSampler"]
```

The service needed for the `traces_sampler` option can be implemented as follows:

`src/Service/Sentry.php`

```php
<?php

namespace App\Service;

class Sentry
{
    public function getTracesSampler(): callable
    {
        return function(\Sentry\Tracing\SamplingContext $context): float {
            // return a number between 0 and 1
        };
    }
}
```

Learn more in [Callables in Symfony Options](https://docs.sentry.io/platforms/php/guides/symfony/configuration/symfony-options.md#callables).

Learn more about tracing [options](https://docs.sentry.io/platforms/php/guides/symfony/configuration/options.md#tracing-options), how to use the [traces\_sampler](https://docs.sentry.io/platforms/php/guides/symfony/configuration/sampling.md#setting-a-sampling-function) function, or how to [sample transactions](https://docs.sentry.io/platforms/php/guides/symfony/configuration/sampling.md#sampling-transaction-events).

## [Verify](https://docs.sentry.io/platforms/php/guides/symfony/tracing.md#verify)

While you're testing, set `traces_sample_rate` to `1.0`, as that ensures that every transaction will be sent to Sentry. Once testing is complete, you may want to set a lower `traces_sample_rate` value or switch to using `traces_sampler` to selectively sample and filter your transactions, based on contextual data.

## [Improve Response Time](https://docs.sentry.io/platforms/php/guides/symfony/tracing.md#improve-response-time)

Response time is somewhat impacted when you use the performance capabilities in your PHP application, (depending on the `traces_sample_rate` you've configured).

If your web server is using FastCGI, our SDK utilizes the [kernel.terminate event](https://symfony.com/doc/current/components/http_kernel.html#8-the-kernel-terminate-event), which means the response is sent to the user before the performance data is sent to Sentry.

If your web server isn't using FastCGI, you can run [Relay](https://docs.sentry.io/product/relay/getting-started.md) locally on the same machine or a local network that can act as a proxy/agent.

Doing this will make the PHP process send requests to your local Relay, which will then forward them to Sentry, instead of sending requests to Sentry directly.

To begin using [Relay](https://docs.sentry.io/product/relay.md), check out our docs for [getting started](https://docs.sentry.io/product/relay/getting-started.md). We recommend using Relay in `managed` mode (which is the default).

Follow the instructions in the Relay docs to send a test event through Relay to Sentry. Don't forget to update your `DSN` to point to your running Relay instance. After you set up Relay, you should see a dramatic improvement to the impact on your server.

## [Next Steps](https://docs.sentry.io/platforms/php/guides/symfony/tracing.md#next-steps)

* #### [Instrumentation](https://docs.sentry.io/platforms/php/guides/symfony/tracing/instrumentation.md)

  Learn how to instrument tracing in your app.

* #### [Trace Propagation](https://docs.sentry.io/platforms/php/guides/symfony/tracing/trace-propagation.md)

  Learn how to connect events across applications/services.

## Pages in this section

- [Instrumentation](https://docs.sentry.io/platforms/php/guides/symfony/tracing/instrumentation.md)
- [Trace Propagation](https://docs.sentry.io/platforms/php/guides/symfony/tracing/trace-propagation.md)