Automatically downsample transaction when system is under load (backpressure)

[adinauer]

📜 Description

Automatically downsample transaction when system is under load by checking:

• if any events have been dropped due to queue being full recently (2s)
• if any rate limit is in effect (regardless of category)

This check is performed every 10 seconds. With each negative health check we halve tracesSampleRate up to 10 times, meaning the original tracesSampleRate is multiplied by 1, 1/2, 1/4, ... up to 1/1024 (~ 0.001%). Any positive health check resets to the original tracesSampleRate set in SentryOptions.

Also see python PRs for reference.

💡 Motivation and Context

Closes #2829

💚 How did you test it?

Unit tests, manually using Spring Boot sample.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	393.41 ms	418.63 ms	25.22 ms
Size	1.72 MiB	2.27 MiB	558.11 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
d6d2b2e	392.55 ms	467.50 ms	74.95 ms
99a51e2	405.11 ms	479.65 ms	74.54 ms
0bd723b	375.20 ms	452.41 ms	77.20 ms
c7e2fbc	377.85 ms	426.35 ms	48.50 ms
b172d4e	412.60 ms	492.68 ms	80.08 ms
4e29063	364.08 ms	445.51 ms	81.43 ms
bc4be3b	360.40 ms	435.04 ms	74.64 ms
93a76ca	397.30 ms	455.16 ms	57.87 ms
8fd337b	349.16 ms	459.22 ms	110.06 ms
93a76ca	377.41 ms	448.22 ms	70.81 ms

App size

Revision	Plain	With Sentry	Diff
d6d2b2e	1.72 MiB	2.27 MiB	555.05 KiB
99a51e2	1.72 MiB	2.29 MiB	576.34 KiB
0bd723b	1.72 MiB	2.29 MiB	578.09 KiB
c7e2fbc	1.72 MiB	2.29 MiB	576.40 KiB
b172d4e	1.72 MiB	2.29 MiB	578.09 KiB
4e29063	1.72 MiB	2.29 MiB	578.38 KiB
bc4be3b	1.72 MiB	2.29 MiB	576.53 KiB
93a76ca	1.72 MiB	2.29 MiB	576.75 KiB
8fd337b	1.72 MiB	2.27 MiB	555.00 KiB
93a76ca	1.72 MiB	2.29 MiB	576.75 KiB

Previous results on branch: feat/backpressure

Startup times

Revision	Plain	With Sentry	Diff
8d081e4	446.34 ms	535.84 ms	89.50 ms
9f06b6e	361.10 ms	430.00 ms	68.90 ms
95f8fd0	415.82 ms	470.54 ms	54.72 ms
3b8dee7	436.04 ms	526.52 ms	90.48 ms

App size

Revision	Plain	With Sentry	Diff
8d081e4	1.72 MiB	2.27 MiB	556.60 KiB
9f06b6e	1.72 MiB	2.27 MiB	556.27 KiB
95f8fd0	1.72 MiB	2.27 MiB	556.38 KiB
3b8dee7	1.72 MiB	2.27 MiB	556.30 KiB

[sl0thentr0py]

one thing you're missing - a new client report (DiscardReason) called backpressure and use that here

sentry-java/sentry/src/main/java/io/sentry/Hub.java

Lines 668 to 670 in 1ad36f1

	options
	.getClientReportRecorder()
	.recordLostEvent(DiscardReason.SAMPLE_RATE, DataCategory.Transaction);

[lbloder]

Left comments on some minor things. Looks good otherwise 👍

Do we want to add the configuration also to the ExternalOptions to make this available to other integrations too?
As far as I can see, enabling backpressureHandling is currently only possible via Spring and the SentryProperties or by supplying SentryOptions in code, correct?

[lbloder]

LGTM, one minor nitpick :)