traces_sampler is not working

[jgrygierek]

Hi, I use laravel 10 + sentry/sentry-laravel 4.15.1.

sentry.php config: 'traces_sampler' => [TracesSampler::class, 'tracesSampler'],

TracesSampler.php class:

<?php

declare(strict_types=1);

namespace App\Sentry;

use Sentry\Tracing\SamplingContext;

class TracesSampler
{
    public static function tracesSampler(SamplingContext $context): float
    {
        $tx = $context->getTransactionContext()?->getName();

        if (
            $tx === '/v1/a/b'
        ) {
            return 0.2;
        }

        return 1.0;
    }
}

I checked it, path is correct, if is ok, 0.2 is returned. But still in Sentry nothing is changed - spans number still is the same like for 1.0.

Any ideas?

[Litarnus]

Hi @jgrygierek!

spans number still is the same like for 1.0

Do you mean by that that the client_sample_rate attribute in spans is still 1.0?

[jgrygierek]

@Litarnus
No, client_sample_rate is set to 0.2.

I want to reduce it, because currently I have too many spans, so limit is reached very quickly. And as I see spans number increase is still not changed.

I have such widget:

And still it is the same as previously.

[Litarnus]

The traces_sample_rate is only used to decide whether you send the entire transaction including all spans or not. So with 0.2 it will send every 5th transaction but the number of spans remain unchanged.

If you want to reduce the number of spans, you have to disable instrumentation: https://docs.sentry.io/platforms/php/guides/laravel/configuration/laravel-options/#more-configuration

You can also reduce the sample rate further so you get less transaction and therefore not reach the limit as fast.

If none of the above suits you, you can also configure a before_send and manually modify the event and remove spans, although I would not recommend this because you might get an incomplete span which may not be very useful.
https://docs.sentry.io/platforms/php/guides/laravel/configuration/filtering/#using-before-send

[jgrygierek]

Sorry, I'm new in Sentry. So basically what traces_sample_rate do? I thought that it reduces transactions number, so spans limit will not be reached so quickly.

[jgrygierek]

More logs:

sentry/sentry: [info] Transaction [...] was started and sampled, decided by config:traces_sampler.
sentry/sentry: [info] Transaction [...] is not profiling because `profiles_sample_rate` option is not set.
sentry/sentry: [info] Sending transaction [...] to ...ingest.de.sentry.io [project:...].
sentry/sentry: [info] Sent transaction [...] to ...ingest.de.sentry.io [project:..]. Result: "success" (status: 200).
sentry/sentry: [warning] The "zend.exception_ignore_args" PHP setting is enabled which results in missing stack trace arguments, see: https://docs.sentry.io/platforms/php/troubleshooting/#missing-variables-in-stack-traces.
sentry/sentry: [debug] The "Sentry\Integration\TransactionIntegration, Sentry\Integration\FrameContextifierIntegration, Sentry\Integration\EnvironmentIntegration, Sentry\Integration\ModulesIntegration, Sentry\Integration\RequestIntegration, Sentry\Laravel\Integration, Sentry\Laravel\Integration\LaravelContextIntegration, Sentry\Laravel\Integration\ExceptionContextIntegration, Sentry\Laravel\Tracing\Integrations\LighthouseIntegration" integration(s) have been installed.
sentry/sentry: [warning] The "zend.exception_ignore_args" PHP setting is enabled which results in missing stack trace arguments, see: https://docs.sentry.io/platforms/php/troubleshooting/#missing-variables-in-stack-traces.
sentry/sentry: [debug] The "Sentry\Integration\TransactionIntegration, Sentry\Integration\FrameContextifierIntegration, Sentry\Integration\EnvironmentIntegration, Sentry\Integration\ModulesIntegration, Sentry\Integration\RequestIntegration, Sentry\Laravel\Integration, Sentry\Laravel\Integration\LaravelContextIntegration, Sentry\Laravel\Integration\ExceptionContextIntegration, Sentry\Laravel\Tracing\Integrations\LighthouseIntegration" integration(s) have been installed.
sentry/sentry: [info] Transaction [...] was started but not sampled, decided by config:traces_sampler.

[cleptric]

config:traces_sampler. A traces sampler overwrites whatever you have set for traces_sample_rate.
So this is the issue.

[jgrygierek]

Yes, and it is ok. I don't use traces_sample_rate. I use traces_sampler :P Like in my first post.

[cleptric]

Sorry, I mixed this up...

Anyways, a route like

Route::get('/v1/a/b', function () {
    return view('welcome');
});

with the provided traces_sampler

'traces_sampler' => function(SamplingContext $context): float {
    $tx = $context->getTransactionContext()?->getName();

    if (
        $tx === '/v1/a/b'
    ) {
        return 0.2;
    }

    return 1.0;
},

filters out ~80% of all transactions and their spans when hitting /v1/a/b.

sentry/sentry: [info] Transaction [5862e6f2182b4ea680293b08358d55ed] was started but not sampled, decided by config:traces_sampler. {"context":{}}
sentry/sentry: [info] Transaction [39021579bdaa4371aa3c148080bac527] was started and sampled, decided by config:traces_sampler. {"context":{}}
sentry/sentry: [info] Transaction [73beea3dc46e45d6a079274f87866387] was started but not sampled, decided by config:traces_sampler. {"context":{}}
sentry/sentry: [info] Transaction [2bffd601e264465992912b6ce3cd1151] was started but not sampled, decided by config:traces_sampler. {"context":{}}
sentry/sentry: [info] Transaction [a137391288d7425e92156681d2d8e325] was started but not sampled, decided by config:traces_sampler. {"context":{}}
sentry/sentry: [info] Transaction [bb1abd9aee4d4053b4aef7eb1dcb7343] was started and sampled, decided by config:traces_sampler. {"context":{}}
sentry/sentry: [info] Transaction [c9d971fbfa894d218c70b37e2f37e057] was started but not sampled, decided by config:traces_sampler. {"context":{}}
sentry/sentry: [info] Transaction [a017ae5163414760a822ced7456d361e] was started but not sampled, decided by config:traces_sampler. {"context":{}}

Right now, I don't know what is going on. If you are willing that we take a look at your org, assuming you use sentry.io, pls provide the details via email or reach out to support.

[jgrygierek]

@cleptric Check your email.