# Set Up Profiling | Sentry for PHP

Profiling for PHP is supported with Sentry PHP SDK version `3.15.0` and above.

With [profiling](https://docs.sentry.io/product/explore/profiling.md), Sentry allows you to collect and analyze performance profiles from real users in production to give you a complete picture of how your application performs in a variety of environments.

Under the hood, we're using Wikipedia's sampling profiler [Excimer](https://github.com/wikimedia/mediawiki-php-excimer). The Excimer PHP extension supports PHP 7.2 and up.

Excimer requires Linux or macOS and doesn't support Windows.

## [Installation](https://docs.sentry.io/platforms/php/profiling.md#installation)

Here's how to install Excimer with a Linux package manager, PECL, or build from a source.

### [Linux Package Manager](https://docs.sentry.io/platforms/php/profiling.md#linux-package-manager)

```bash
apt-get install php-excimer
```

See <https://www.mediawiki.org/wiki/Excimer> for additional distributions.

### [PECL](https://docs.sentry.io/platforms/php/profiling.md#pecl)

```bash
pecl install excimer
```

See <https://pecl.php.net/package/excimer> for more information.

### [Build from source](https://docs.sentry.io/platforms/php/profiling.md#build-from-source)

```bash
git clone https://github.com/wikimedia/mediawiki-php-excimer.git

cd excimer/
phpize && ./configure && make && sudo make install
```

Depending on your environment, you may need to enable the Excimer extension afterwards.

```bash
phpenmod -s fpm excimer
# or
phpenmod -s apache2 excimer
```

## [Enable Tracing](https://docs.sentry.io/platforms/php/profiling.md#enable-tracing)

Sentry's tracing product has to be enabled in order for Profiling to work. To begin capturing profiling data, you first need to start a transaction. Check out the [performance setup](https://docs.sentry.io/platforms/php/tracing.md) and [custom instrumentation](https://docs.sentry.io/platforms/php/tracing/instrumentation/custom-instrumentation.md) documentation for more detailed information.

```php
\Sentry\init([
    'dsn' => '___PUBLIC_DSN___',
    'traces_sample_rate' => 1.0,
]);
```

## [Enabling Profiling](https://docs.sentry.io/platforms/php/profiling.md#enabling-profiling)

```php
\Sentry\init([
    'dsn' => '___PUBLIC_DSN___',
    'traces_sample_rate' => 1.0,
    // Set a sampling rate for profiling - this is relative to traces_sample_rate
    'profiles_sample_rate' => 1.0,
]);
```

## [Improve Response Time](https://docs.sentry.io/platforms/php/profiling.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). This is due to the nature of PHP, where requests are usually sent as part of the process in which you serve your users' response. This affects the time it takes to send a request to Sentry because it's added to your servers' response time.

To offset this and make the addition close to zero, 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, 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've set up Relay, you should see a dramatic improvement in how much your server is impacted.