enhancement(core): Erlang/OTP-style supervisor system by tobz · Pull Request #629 · DataDog/saluki

tobz · 2025-04-21T13:05:00Z

Summary

This PR introduces a new runtime system in saluki-core modeled after Erlang/OTP's supervision trees, a powerful design pattern for building fault-tolerant systems composed of many interdependent "processes" in a way that they can recover from failure.

Supervision trees are explained succinctly by the Erlang/OTP documentation, but generally: we have a collection of processes (asynchronous tasks) that have some level of fallibility, and we want to -- where possible -- maximize their resilience by allowing them to be restarted if they fail. Supervision trees approach this from the perspective of declaring a "specification" that describes how to create the process (in our case, building the Future that is spawned) and then adding those specifications to a supervisor, which is responsible for managing those processes, restarting them when die, giving up if certain restart limits are hit, and so on.

While we lack a lot of the power of Erlang itself, in terms of what Erlang/OTP's supervisors can build on top of, even having the basics provides us a lot of leeway for building things in a more fault-tolerant way:

restarting crashed topology components, or arbitrary background tasks, in a uniform and consistent way
providing the scaffolding to track all active tasks and how they're nested
ordered shutdown for everything instead of just the topology

We're intentionally only implementing many of the basics here -- worker specification, restart strategy, nested supervisors, orderly shutdown, etc -- but will add enhanced capabilities in future iterations, such as runtime telemetry/introspection, dynamic workers, and more.

Change Type

Bug fix
New feature
Non-functional (chore, refactoring, docs)
Performance

How did you test this PR?

N/A

References

AGTMETRICS-233

pr-commenter · 2025-09-30T01:11:02Z

Regression Detector (Agent Data Plane)

Regression Detector Results

Run ID: 0546c77b-62eb-48c2-825b-d04173cd8996

Baseline: 0957bb3
Comparison: e09fddb
Diff

Optimization Goals: ✅ No significant changes detected

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI	trials
➖	quality_gates_rss_dsd_medium	memory utilization	+0.30	[+0.12, +0.47]	1
➖	quality_gates_rss_dsd_heavy	memory utilization	+0.29	[+0.19, +0.38]	1
➖	quality_gates_rss_idle	memory utilization	+0.17	[+0.15, +0.19]	1
➖	dsd_uds_10mb_3k_contexts_throughput	ingress throughput	+0.03	[-0.02, +0.08]	1
➖	dsd_uds_512kb_3k_contexts_throughput	ingress throughput	+0.00	[-0.01, +0.02]	1
➖	quality_gates_rss_dsd_ultraheavy	ingress throughput	+0.00	[-0.04, +0.04]	1
➖	dsd_uds_1mb_3k_contexts_throughput	ingress throughput	-0.00	[-0.02, +0.01]	1
➖	dsd_uds_100mb_3k_contexts_throughput	ingress throughput	-0.01	[-0.08, +0.06]	1
➖	quality_gates_rss_dsd_low	memory utilization	-0.07	[-0.22, +0.07]	1
➖	dsd_uds_500mb_3k_contexts_throughput	ingress throughput	-3.41	[-3.54, -3.27]	1

Bounds Checks: ✅ Passed

perf	experiment	bounds_check_name	replicates_passed
✅	quality_gates_rss_dsd_heavy	memory_usage	10/10
✅	quality_gates_rss_dsd_low	memory_usage	10/10
✅	quality_gates_rss_dsd_medium	memory_usage	10/10
✅	quality_gates_rss_dsd_ultraheavy	memory_usage	10/10
✅	quality_gates_rss_idle	memory_usage	10/10

Explanation

Confidence level: 90.00%
Effect size tolerance: |Δ mean %| ≥ 5.00%

Performance changes are noted in the perf column of each table:

✅ = significantly better comparison variant performance
❌ = significantly worse comparison variant performance
➖ = no significant change in performance

A regression test is an A/B test of target performance in a repeatable rig, where "performance" is measured as "comparison variant minus baseline variant" for an optimization goal (e.g., ingress throughput). Due to intrinsic variability in measuring that goal, we can only estimate its mean value for each experiment; we report uncertainty in that value as a 90.00% confidence interval denoted "Δ mean % CI".

For each experiment, we decide whether a change in performance is a "regression" -- a change worth investigating further -- if all of the following criteria are true:

Its estimated |Δ mean %| ≥ 5.00%, indicating the change is big enough to merit a closer look.
Its 90.00% confidence interval "Δ mean % CI" does not contain zero, indicating that if our statistical model is accurate, there is at least a 90.00% chance there is a difference in performance between baseline and comparison variants.
Its configuration does not mark it "erratic".

pr-commenter · 2025-09-30T01:12:00Z

Regression Detector (Agent Data Plane w/ Checks)

Regression Detector Results

Run ID: 9136ff2d-887d-4d14-b93e-b9227939eed7

Baseline: 0957bb3
Comparison: e09fddb
Diff

Optimization Goals: ✅ No significant changes detected

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	quality_gates_rss_idle	memory utilization	+0.02	[+0.01, +0.04]	1
➖	quality_gates_rss_basic	memory utilization	-0.14	[-0.16, -0.13]	1

Bounds Checks: ✅ Passed

perf	experiment	bounds_check_name	replicates_passed	links
✅	quality_gates_rss_basic	memory_usage	10/10
✅	quality_gates_rss_idle	memory_usage	10/10

Explanation

Confidence level: 90.00%
Effect size tolerance: |Δ mean %| ≥ 5.00%

Performance changes are noted in the perf column of each table:

✅ = significantly better comparison variant performance
❌ = significantly worse comparison variant performance
➖ = no significant change in performance

A regression test is an A/B test of target performance in a repeatable rig, where "performance" is measured as "comparison variant minus baseline variant" for an optimization goal (e.g., ingress throughput). Due to intrinsic variability in measuring that goal, we can only estimate its mean value for each experiment; we report uncertainty in that value as a 90.00% confidence interval denoted "Δ mean % CI".

For each experiment, we decide whether a change in performance is a "regression" -- a change worth investigating further -- if all of the following criteria are true:

Its estimated |Δ mean %| ≥ 5.00%, indicating the change is big enough to merit a closer look.
Its 90.00% confidence interval "Δ mean % CI" does not contain zero, indicating that if our statistical model is accurate, there is at least a 90.00% chance there is a difference in performance between baseline and comparison variants.
Its configuration does not mark it "erratic".

pr-commenter · 2025-09-30T01:13:02Z

Regression Detector Links

ADP Experiment Result Links

experiment	link(s)
dsd_uds_100mb_3k_contexts_throughput	[Profiling] [SMP Dashboard]
dsd_uds_10mb_3k_contexts_throughput	[Profiling] [SMP Dashboard]
dsd_uds_1mb_3k_contexts_throughput	[Profiling] [SMP Dashboard]
dsd_uds_500mb_3k_contexts_throughput	[Profiling] [SMP Dashboard]
dsd_uds_512kb_3k_contexts_throughput	[Profiling] [SMP Dashboard]
quality_gates_rss_dsd_heavy	[Profiling] [SMP Dashboard]
quality_gates_rss_dsd_low	[Profiling] [SMP Dashboard]
quality_gates_rss_dsd_medium	[Profiling] [SMP Dashboard]
quality_gates_rss_dsd_ultraheavy	[Profiling] [SMP Dashboard]
quality_gates_rss_idle	[Profiling] [SMP Dashboard]

ADP && Checks Experiment Result Links

experiment	link(s)
quality_gates_rss_basic	[Profiling] [SMP Dashboard]
quality_gates_rss_idle	[Profiling] [SMP Dashboard]

blt · 2025-10-02T18:40:18Z

lib/saluki-core/src/runtime/mod.rs

+//! Processes have a few key attributes and invariants:
+//!
+//! - every process is a future that runs as an independent asynchronous task on a Tokio runtime
+//! - every process has a unique numerical identifier and a semi-unique name
+//!
+//! Processes cannot run by themselves, however. They must be _supervised_.


Confirming, unlike Erlang processes saluki-core processes do not have a mailbox / input queue associated for message passing?

Confirmed later, no mailbox. Probably worth adding this to the documentation in case someone -- like myself -- comes along with an Erlang mental model inappropriately.

Yep, that's correct.

Fixed in 92f4d85.

blt · 2025-10-02T18:42:21Z

lib/saluki-core/src/runtime/process.rs

+/// Process names will be sanitized if they contain invalid characters, such as hyphens or spaces. Invalid characters
+/// will be replaced with underscores.


I'm not opposed, just curious why we don't reject invalid names outright? Haven't confirmed yet, it's possible the intention here is for process names to arrive via user config, in which case this does make some sense.

Yeah, more or less. Process names will come, in part, from user-defined identifiers that might be provided at a layer above (or higher) the point where processes themselves are constructed, so we want to be more liberal in what we accept so that code doesn't have to bubble up that sort of constraint.

blt · 2025-10-02T18:50:26Z

lib/saluki-core/src/runtime/supervisor.rs

+                    // TODO: Erlang/OTP defaults to always trying to restart a process, even if it doesn't terminate due to a
+                    // legitimate failure. It does allow configuring this behavior on a per-process basis, however. We don't
+                    // support dynamically adding child processes, which is the only real use case I can think of for having
+                    // non-long-lived child processes... so I think for now, we're OK just always try to restart.


blt · 2025-10-02T18:55:10Z

lib/saluki-core/examples/basic_supervisor.rs

@@ -0,0 +1,175 @@
+use std::time::Duration;


I like how the API works. Probably worth developing a lint or something to confirm that processes actually check their shutdown signal properly. Shame we don't have the ability to preempt.

…x unlike erlang processes

pr-commenter · 2026-01-31T21:58:03Z

Binary Size Analysis (Agent Data Plane)

Target: aec6cab (baseline) vs 9b198f6 (comparison) diff
Analysis Type: Stripped binaries (debug symbols excluded)
Baseline Size: 27.62 MiB
Comparison Size: 27.62 MiB
Size Change: -952 B (-0.00%)
Pass/Fail Threshold: +5%
Result: PASSED ✅

Changes by Module

Module	File Size	Symbols
[Unmapped]	+1.58 KiB	1
_ZN4http6header4name14StandardHeader6as_str17hb45bedc01a2a74c0E.10085	+1.10 KiB	1
_ZN4http6header4name14StandardHeader6as_str17hb45bedc01a2a74c0E.10093	-1.10 KiB	1
_ZN4http6header4name14StandardHeader6as_str17hb45bedc01a2a74c0E.8471	+1.10 KiB	1
_ZN4http6header4name14StandardHeader6as_str17hb45bedc01a2a74c0E.8776	+1.10 KiB	1
_ZN4http6header4name14StandardHeader6as_str17hb45bedc01a2a74c0E.9046	+1.10 KiB	1
_ZN4http6header4name14StandardHeader6as_str17hb45bedc01a2a74c0E.8479	-1.10 KiB	1
_ZN4http6header4name14StandardHeader6as_str17hb45bedc01a2a74c0E.8784	-1.10 KiB	1
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_ZN4http6header4name14StandardHeader6as_str17hb45bedc01a2a74c0E.10810	-1.10 KiB	1
_ZN17crossbeam_channel5waker9SyncWaker6notify17h0ddc00b08af3a086E.13817	+1.08 KiB	1
_ZN17crossbeam_channel5waker9SyncWaker6notify17h0ddc00b08af3a086E.13814	-1.08 KiB	1
_ZN17crossbeam_channel5waker9SyncWaker6notify17h0ddc00b08af3a086E.8764	+1.00 KiB	1
_ZN17crossbeam_channel5waker9SyncWaker6notify17h0ddc00b08af3a086E.8772	-1.00 KiB	1
_ZN17crossbeam_channel5waker9SyncWaker10disconnect17h5a7a3d8762979030E.8759	+952 B	1
_ZN17crossbeam_channel5waker9SyncWaker10disconnect17h5a7a3d8762979030E.8767	-952 B	1
_ZN12regex_syntax3hir3Hir5class17hebf341d170d5a49fE.9955	+896 B	1
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_ZN5seize3raw9collector9Collector10try_retire17h5d92677642bd7678E.11141	+880 B	1

Detailed Symbol Changes

    FILE SIZE        VM SIZE    
 --------------  -------------- 
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  [NEW] +5.35Ki  [NEW] +5.23Ki    _ZN59_<rustls::error::Error as core::clone::Clone>5clone17hd14a1219ce5dde1cE.10806
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  -0.1%    -952  -0.2% -1.58Ki    [471 Others]
  [DEL] -3.57Ki  [DEL] -3.45Ki    _ZN57_<rustls::error::Error as core::fmt::Debug>3fmt17hc5ecb86b7cbe8c88E.10017
  [DEL] -3.58Ki  [DEL] -3.46Ki    _ZN57_<rustls::error::Error as core::fmt::Debug>3fmt17hc5ecb86b7cbe8c88E.11791
  [DEL] -3.67Ki  [DEL] -3.56Ki    _ZN57_<rustls::error::Error as core::fmt::Debug>3fmt17hc5ecb86b7cbe8c88E.10265
  [DEL] -3.83Ki  [DEL] -3.71Ki    _ZN57_<webpki::error::Error as core::fmt::Debug>3fmt17h9036eab966a4f655E.12023
  [DEL] -4.25Ki  [DEL] -4.13Ki    _ZN59_<rustls::error::Error as core::clone::Clone>5clone17hd14a1219ce5dde1cE.10112
  [DEL] -4.75Ki  [DEL] -4.62Ki    _ZN76_<saluki_core::data_model::event::Event as core::clone::Clone>5clone17h7f500b934c4a671bE.10789
  [DEL] -5.21Ki  [DEL] -5.09Ki    _ZN59_<rustls::error::Error as core::clone::Clone>5clone17hd14a1219ce5dde1cE.11866
  [DEL] -5.35Ki  [DEL] -5.23Ki    _ZN59_<rustls::error::Error as core::clone::Clone>5clone17hd14a1219ce5dde1cE.10814
  [DEL] -5.52Ki  [DEL] -5.39Ki    _ZN76_<hickory_proto::rr::record_data::RData as core::clone::Clone>5clone17h61f3fe4fffa4b03dE.11903
  [DEL] -6.13Ki  [DEL] -6.00Ki    _ZN76_<hickory_proto::rr::record_data::RData as core::clone::Clone>5clone17h61f3fe4fffa4b03dE.8776
  -0.0%    -952  -0.0% -1.58Ki    TOTAL

github-actions bot added the area/core Core functionality, event model, etc. label Apr 21, 2025

tobz changed the title ~~experiment: Erlang/OTP-style supervisor system~~ [AGTMETRICS-184] experiment: Erlang/OTP-style supervisor system Apr 23, 2025

tobz force-pushed the tobz/erlang-otp-style-supervisor-system branch from dc6c05f to 343860d Compare May 8, 2025 18:40

tobz force-pushed the tobz/erlang-otp-style-supervisor-system branch from 343860d to 9840350 Compare May 25, 2025 13:04

tobz force-pushed the tobz/erlang-otp-style-supervisor-system branch 2 times, most recently from ed00477 to 74574e9 Compare June 16, 2025 23:46

tobz force-pushed the tobz/erlang-otp-style-supervisor-system branch from e2c007a to feb74bb Compare June 17, 2025 13:41

tobz force-pushed the tobz/erlang-otp-style-supervisor-system branch from feb74bb to 125372c Compare September 12, 2025 19:21

tobz force-pushed the tobz/erlang-otp-style-supervisor-system branch from 125372c to 4a63c4e Compare September 23, 2025 14:46

github-actions bot added area/io General I/O and networking. area/config Configuration. area/components Sources, transforms, and destinations. area/memory Memory bounds and memory management. labels Sep 23, 2025

tobz force-pushed the tobz/erlang-otp-style-supervisor-system branch from 4a63c4e to 0de68dc Compare September 28, 2025 12:59

tobz force-pushed the tobz/erlang-otp-style-supervisor-system branch from 581b0f6 to bf3527b Compare September 29, 2025 20:10

github-actions bot removed the area/ci CI/CD, automated testing, etc. label Sep 29, 2025

blt approved these changes Oct 2, 2025

View reviewed changes

tobz and others added 3 commits October 17, 2025 11:36

fix(env): remove aliases for cgroups that are removed at runtime (#772)

5a18a7b

update description of saluki processes to mention they have no mailbo…

92f4d85

…x unlike erlang processes

Merge branch 'main' into tobz/erlang-otp-style-supervisor-system

9b198f6

		/// Process names will be sanitized if they contain invalid characters, such as hyphens or spaces. Invalid characters
		/// will be replaced with underscores.

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tobz commented Apr 21, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

Change Type

How did you test this PR?

References

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pr-commenter bot commented Sep 30, 2025

Regression Detector (Agent Data Plane)

Regression Detector Results

Optimization Goals: ✅ No significant changes detected

Fine details of change detection per experiment

Bounds Checks: ✅ Passed

Explanation

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pr-commenter bot commented Sep 30, 2025

Regression Detector (Agent Data Plane w/ Checks)

Regression Detector Results

Optimization Goals: ✅ No significant changes detected

Fine details of change detection per experiment

Bounds Checks: ✅ Passed

Explanation

Uh oh!

pr-commenter bot commented Sep 30, 2025

Regression Detector Links

ADP Experiment Result Links

ADP && Checks Experiment Result Links

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pr-commenter bot commented Jan 31, 2026

Binary Size Analysis (Agent Data Plane)

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tobz commented Apr 21, 2025 •

edited

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