feat(tracing): Use `sample_rand` for sampling decisions #4044

szokeasaurusrex · 2025-02-12T11:40:13Z

Use the sample_rand value from an incoming trace to make sampling decisions, rather than generating a random value. When we are the head SDK starting a new trace, save our randomly-generated value as the sample_rand, and also change the random generation logic so that the sample_rand is computed deterministically based on the trace_id.

Depends on:

Closes #3998

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codecov · 2025-02-12T11:41:53Z

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.59%. Comparing base (61ae6e7) to head (0d49ac2).
Report is 1 commits behind head on szokeasaurusrex/sample_rand-3.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@                        Coverage Diff                        @@
##           szokeasaurusrex/sample_rand-3    #4044      +/-   ##
=================================================================
+ Coverage                          79.55%   79.59%   +0.03%     
=================================================================
  Files                                140      140              
  Lines                              15570    15579       +9     
  Branches                            2641     2643       +2     
=================================================================
+ Hits                               12387    12400      +13     
+ Misses                              2343     2341       -2     
+ Partials                             840      838       -2

Files with missing lines	Coverage Δ
sentry_sdk/tracing.py	`77.73% <100.00%> (+0.13%)`	⬆️
sentry_sdk/tracing_utils.py	`85.50% <100.00%> (+0.21%)`	⬆️

... and 3 files with indirect coverage changes

sentrivana · 2025-02-13T14:36:20Z

sentry_sdk/tracing.py

+        if baggage_sample_rand is not None:
+            self._sample_rand = baggage_sample_rand
+        else:
+            self._sample_rand = Random(self.trace_id).random()


In what cases will we have to generate a new _sample_rand here?

Whenever we are starting a new trace, i.e. if we call start_transaction without calling continue_trace first and without manually passing in baggage

sl0thentr0py

just comments on the tests, testing exact float values like that can be non-deterministic so maybe better to just mock out the rng

tests/integrations/celery/test_celery.py

sl0thentr0py · 2025-02-20T12:42:05Z

tests/tracing/test_sample_rand.py

+
+TEST_TRACE_ID_SAMPLE_RANDS = {
+    "00000000000000000000000000000000": 0.8766381713144122,
+    "01234567012345670123456701234567": 0.6451742521664413,


also not sure if rng is consistent like that across python versions and so on?

sentrivana

Looks ok -- please see comments

sentrivana · 2025-02-25T11:22:49Z

tests/integrations/aiohttp/test_aiohttp.py

@@ -636,7 +636,7 @@ async def handler(request):

        assert (
            resp.request_info.headers["baggage"]
-            == "custom=value,sentry-trace_id=0123456789012345678901234567890,sentry-environment=production,sentry-release=d08ebdb9309e1b004c6f52202de58a09c2268e42,sentry-transaction=/interactions/other-dogs/new-dog,sentry-sample_rate=1.0,sentry-sampled=true"
+            == "custom=value,sentry-trace_id=0123456789012345678901234567890,sentry-sample_rand=0.3015579701611357,sentry-environment=production,sentry-release=d08ebdb9309e1b004c6f52202de58a09c2268e42,sentry-transaction=/interactions/other-dogs/new-dog,sentry-sample_rate=1.0,sentry-sampled=true"


Shouldn't sample_rand have 6 digits after the decimal point?

sentrivana · 2025-02-25T11:25:06Z

tests/tracing/test_sample_rand.py

+import sentry_sdk
+from sentry_sdk.tracing_utils import Baggage
+
+TEST_TRACE_ID_SAMPLE_RANDS = {


These too -- aren't they supposed to have 6 decimal places?

Use the `sample_rand` value from an incoming trace to make sampling decisions, rather than generating a random value. When we are the head SDK starting a new trace, save our randomly-generated value as the `sample_rand`, and also change the random generation logic so that the `sample_rand` is computed deterministically based on the `trace_id`. Closes #3998

szokeasaurusrex force-pushed the szokeasaurusrex/sample_rand-4 branch from c3d6d12 to 5a906f6 Compare February 12, 2025 11:42

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szokeasaurusrex marked this pull request as ready for review February 12, 2025 13:36

szokeasaurusrex requested review from sentrivana and sl0thentr0py February 12, 2025 13:36

szokeasaurusrex linked an issue Feb 12, 2025 that may be closed by this pull request

Implement Sampling Seed Propagation #3998

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sentrivana reviewed Feb 13, 2025

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feat(tracing): Backfill missing sample_rand on PropagationContext #4038

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sentrivana merged commit ccb969e into szokeasaurusrex/sample_rand-3 Feb 26, 2025
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sentrivana deleted the szokeasaurusrex/sample_rand-4 branch February 26, 2025 14:39

szokeasaurusrex mentioned this pull request Mar 24, 2025

Implement Sampling Seed Propagation #3998

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