feat: queue time capture for Rack by dingsdax · Pull Request #2838 · getsentry/sentry-ruby

dingsdax · 2026-01-15T10:20:31Z

Captures how long requests wait for a e.g. Puma thread from X-Request-Start headers and attaches it to transactions as http.queue_time_ms. Sentry only measures after Puma picks up the request. Under load, requests might wait long in the queue but only take a fraction to process. Similar to what judoscale and scout do.

works with all major reverse proxies:

Nginx: X-Request-Start: t=1234567890.123 (seconds)
Heroku: X-Request-Start: t=1234567890123456 (microseconds)
HAProxy 1.9+: X-Request-Start: t=1234567890123456 (microseconds)
HAProxy < 1.9: X-Request-Start: t=1234567890 (seconds)
Generic: Raw timestamps in seconds/milliseconds/microseconds

subtracts puma.request_body_wait for accuracy (excludes slow client uploads from queue time).

Usage

works 🤞 if your reverse proxy sets the header:

# Nginx
proxy_set_header X-Request-Start "t=${msec}";

opt-out

config.capture_queue_time = false

resolves: Add Puma request queue time as a transaction attribute #2813
resolves: RUBY-130

default to true

linear · 2026-01-15T10:20:35Z

RUBY-130 Add Puma request queue time as a transaction attribute

github-actions · 2026-01-15T10:20:57Z

	Messages
📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

Generated by 🚫 dangerJS against 00cc056

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

sl0thentr0py · 2026-01-15T13:03:58Z

sentry-ruby/lib/sentry/span.rb

      MESSAGING_MESSAGE_RETRY_COUNT = "messaging.message.retry.count"
+
+      # Time in ms the request spent in the server queue before processing began.
+      HTTP_QUEUE_TIME_MS = "http.queue_time_ms"


@AbhiPrasad @lcian is there an attribute convention for time spent in queue waiting for the http request to be picked up in an HTTP server?

The closest I could find is http.client.request.time_in_queue but that's for clients.

Hmmm I cannot find anything like that. Maybe we introduce our own http.server.request.time_in_queue counterpart?

sounds good; shall I add to sentry-conventions too?

sl0thentr0py

some small stuff, and mainly want to wait for feedback on the attribute convention name

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

sl0thentr0py · 2026-01-15T13:13:03Z

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

+        total_time_ms = ((Time.now.to_f - request_start) * 1000).round(2)
+
+        # reject negative (clock skew between proxy & app server) or very large values (> 60 seconds)
+        return nil unless total_time_ms >= 0 && total_time_ms < 60_000


not sure about the upper bound here, would still be useful to know right?

wdym? remove upper bound here? should be fine too

yes let's remove the upper bound

sentry-ruby/test-app/sentry_queue_test.rb

sentry-ruby/spec/sentry/rack/capture_exceptions_spec.rb

Co-authored-by: Neel Shah <neel.shah@sentry.io>

cursor · 2026-01-15T17:40:22Z

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

+          header_value.to_f
+        else
+          return nil
+        end


Non-numeric t= prefixed header values produce incorrect queue time

Medium Severity

The parse_request_start_header function validates format with a regex for raw numeric timestamps but not for t= prefixed values. When receiving a malformed header like t=invalid, "invalid".to_f silently returns 0.0 (Ruby's behavior for non-numeric strings). This results in a timestamp of Unix epoch (1970), causing the queue time calculation to return ~56 years of queue time instead of nil. The issue affects any malformed t= prefixed header value including t=, t=abc, etc.

solnic

✅ but I left a bunch of minor 💅🏻 suggestions 🙃

solnic · 2026-01-26T14:56:57Z

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

+      # @param env [Hash] Rack env
+      # @return [Float, nil] queue time in milliseconds or nil
+      def extract_queue_time(env)
+        return nil unless Sentry.configuration&.capture_queue_time


Suggested change

return nil unless Sentry.configuration&.capture_queue_time

return unless Sentry.configuration&.capture_queue_time

solnic · 2026-01-26T14:57:07Z

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

+        return nil unless Sentry.configuration&.capture_queue_time
+
+        header_value = env["HTTP_X_REQUEST_START"]
+        return nil unless header_value


Suggested change

return nil unless header_value

return unless header_value

solnic · 2026-01-26T14:57:14Z

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

+        return nil unless header_value
+
+        request_start = parse_request_start_header(header_value)
+        return nil unless request_start


Suggested change

return nil unless request_start

return unless request_start

solnic · 2026-01-26T14:57:22Z

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

+        total_time_ms = ((Time.now.to_f - request_start) * 1000).round(2)
+
+        # reject negative (clock skew between proxy & app server)
+        return nil unless total_time_ms >= 0


Suggested change

return nil unless total_time_ms >= 0

return unless total_time_ms >= 0

solnic · 2026-01-26T14:58:06Z

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

+          total_time_ms
+        end
+      rescue StandardError
+        nil


Suggested change

nil

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

solnic · 2026-01-26T14:58:31Z

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

+        elsif header_value.match?(/\A\d+(?:\.\d+)?\z/)
+          header_value.to_f
+        else
+          return nil


Suggested change

return nil

return

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

Co-authored-by: Peter Solnica <peter@solnica.online>

dingsdax added 3 commits January 15, 2026 09:41

add configuration for capturing queue time

39a875b

default to true

Extract, normalize & add queue time to transaction

8b2e2b8

Test app for queue time in Sentry

7829e24

github-advanced-security bot found potential problems Jan 15, 2026

View reviewed changes

sentry-ruby/lib/sentry/rack/capture_exceptions.rb Fixed Show fixed Hide fixed

dingsdax requested review from sl0thentr0py and solnic and removed request for solnic January 15, 2026 10:22

dingsdax marked this pull request as ready for review January 15, 2026 10:23

dingsdax added 4 commits January 15, 2026 11:26

Fix redos issue

dfea02f

move test app

c223fce

Update CHANGELOG.md

597c2e6

Update CHANGELOG.md

9f3bd01

dingsdax mentioned this pull request Jan 15, 2026

feat: queue time metric getsentry/sentry-docs#16030

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sl0thentr0py reviewed Jan 15, 2026

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sl0thentr0py requested changes Jan 15, 2026

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dingsdax and others added 5 commits January 15, 2026 14:25

Update sentry-ruby/lib/sentry/rack/capture_exceptions.rb

1407b7d

Co-authored-by: Neel Shah <neel.shah@sentry.io>

Delete sentry_queue_test.rb

f5e132b

⏰👮🏻

13cd936

change name

b32132c

remove upper bounds

00cc056

cursor bot reviewed Jan 15, 2026

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sl0thentr0py approved these changes Jan 16, 2026

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solnic approved these changes Jan 26, 2026

View reviewed changes

dingsdax and others added 2 commits January 26, 2026 16:25

Update sentry-ruby/lib/sentry/rack/capture_exceptions.rb

39b76a3

Co-authored-by: Peter Solnica <peter@solnica.online>

Update sentry-ruby/lib/sentry/rack/capture_exceptions.rb

6f0fc54

Co-authored-by: Peter Solnica <peter@solnica.online>

	return nil unless Sentry.configuration&.capture_queue_time
	return unless Sentry.configuration&.capture_queue_time

	return nil unless total_time_ms >= 0
	return unless total_time_ms >= 0

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Non-numeric `t=` prefixed header values produce incorrect queue time