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Priority band for the pending set, enqueued_at instrumentation, and a retryable-starvation fix - #13
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Included review availability: 3 reviews are currently available. Your included PR review attempts over the past 7 days set your current allowance at 5 reviews per hour. 📝 WalkthroughWalkthroughRedis notifications now support priority-based pending ordering and enqueue-age tracking. Redis delivery allocates poll capacity between pending and due retryable notifications. Redis test setup now mirrors app records into ActiveRecord. CI uses Ubuntu 22.04 and a constrained ChangesRedis notification delivery
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to When the poll budget is one, a continuously due retry can still prevent pending notifications from being selected, delaying their delivery. The change is otherwise mergeable, but this bounded starvation case should be explicitly addressed or accepted by the owner. Sequence Diagram(s)sequenceDiagram
participant Notification
participant PendingSet
participant RedisStore
participant RetryableSet
Notification->>Notification: stamp enqueued_at
Notification->>PendingSet: register pending_score
RedisStore->>RetryableSet: claim capped due retryables
RedisStore->>PendingSet: claim remaining poll capacity
RedisStore->>RetryableSet: claim unused capacity
RetryableSet-->>RedisStore: return claimed retryable IDs
🚥 Pre-merge checks | ✅ 2 | ❌ 3❌ Failed checks (2 warnings, 1 inconclusive)
✅ Passed checks (2 passed)
Full details: Linked Issues checkExplanation The Ubuntu runner update and sqlite3 version constraint address issue Resolution Provide reviewable evidence that Gemfile.lock includes the x86_64-linux platform and that the full-daemon functional specs and two shared-store app-lookup examples are skipped for the Redis client, or adjust the linked issue and implementation to document the alternative test-harness approach. Full details: Out of Scope Changes checkExplanation The priority-band changes, enqueued_at and age_ms instrumentation, retryable claim allocation, and related unit tests are unrelated to the requirements in issue Full details: Docstring CoverageExplanation Docstring coverage is 31.82% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 22 functions across 10 files. (1 skipped: 1 unsupported.)
✨ Finishing Touches 💡 1📝 Generate docstrings 💡
🧪 Generate unit tests (beta)
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Inline comments:
In `@lib/rpush/daemon/store/redis.rb`:
- Line 35: Update the pending budget calculation in the Redis store flow so a
limit of one still permits delivery of pending work when no retry is due, while
preserving the intended retry fairness for larger limits. Define the one-slot
policy explicitly and add a regression covering pending work with no due retry,
using pending_budget and deliverable_notifications as the relevant symbols.
- Around line 206-213: Update the retry-claim logic around the Redis transaction
in the daemon store so selection and removal are atomic and restricted to
members with scores no greater than now. Remove the rank-based
zrange/zremrangebyrank approach, use an atomic script or equivalent that returns
and deletes the exact due members, and add concurrent-claimer coverage verifying
future retries remain queued.
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lib/rpush/client/redis/notification.rblib/rpush/daemon/store/redis.rbspec/unit/client/redis/notification_spec.rbspec/unit/daemon/store/redis_spec.rb
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Inline comments:
In `@lib/rpush/daemon/store/redis.rb`:
- Line 244: Update retryable_budget or the deliverable_notifications allocation
logic so repeated single-slot polls do not always give the slot to retryable
notifications when both retryable and pending sources have work; alternate the
selected source across calls while preserving the existing capacity limits. Add
a regression covering repeated deliverable_notifications(1) calls with both sets
nonempty and verify that each source makes progress.
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GitHub retired the ubuntu-20.04 hosted runner image, so every matrix job sat queued forever with no runner. Bump to ubuntu-22.04, which still provides prebuilt Ruby 2.7 / 3.0 / 3.1 via ruby/setup-ruby (unlike ubuntu-24.04).
The lockfile listed only the ruby platform, so bundler compiled sqlite3 from source on every job, which fails to build on ubuntu-22.04. Pin sqlite3 to the 1.6.x line (the last that ships precompiled x86_64-linux binaries for Ruby 2.7, production version) and add x86_64-linux to the lock so bundler installs the prebuilt gem. sqlite3 is a test-only dependency; production rpush uses redis.
Production reads apps from ActiveRecord even under the redis client (Store::Redis#all_apps / #app), while the upstream specs only create Redis apps, so the redis matrix could never find its app and every functional scenario timed out. Mirror every Redis app into ActiveRecord under the same id (test-only, matching how production keeps them in sync), load the AR schema under both clients, re-enable the Feedback all-index for tests, and compare store apps by id (the hybrid store returns an AR representation).
The Redis pending set is scored `zadd(pending, id, id)`, so delivery is strict
FIFO across every app. A large campaign therefore places its whole fan-out ahead
of every subsequent transactional push. Measured downstream at Thanx: order-status
notifications averaged 296.7s and peaked at 4,544s from creation to APNs/FCM
handoff, against a 120s target, while sitting behind campaign backlogs 10,000 to
43,363 deep for 10-15 minutes at a time.
Adds `priority_class` (default 1) and scores the pending set as
((priority_class - PRIORITY_CLASS_DEFAULT) * PRIORITY_CLASS_BAND) + id
The claim path needs no change: pending_notification_ids already claims by RANK
(ZRANGE 0..limit + ZREMRANGEBYRANK 0..limit), and ordering the score is therefore
sufficient to order delivery.
The band is anchored on the DEFAULT class rather than on zero, so a notification
at the default scores exactly its own id. That is deliberate and load-bearing:
the pending set stays byte-identical to pre-priority behaviour for every existing
caller, so there is no transition window while a mixed-version fleet rolls, no
score inversion between old and new writers, and a revert is score-safe. A class
below the default scores negative and sorts ahead of all default traffic.
`|| PRIORITY_CLASS_DEFAULT` is used rather than `.to_i` when reading the class:
nil.to_i is 0, which would silently PROMOTE a notification whose priority_class
failed to load into the highest band. Falling back to the default is inert.
Also adds `enqueued_at` plus an `age_ms` reader, because nothing in this model
records creation time -- there is no created_at attribute -- so the time a
notification spent between being enqueued and being handed to the push service
was previously unmeasurable. It is stamped by a before_create callback rather
than an attribute default: Modis evaluates `default:` once at class-definition
time, so `default: Time.now` would brand every notification with the timestamp
of process boot. age_ms returns nil for notifications that predate the attribute,
and callers must handle that.
CO-REQUISITE: the retryable-budget fix in the following commit. Priority ordering
alone does not deliver the latency win, because a deep retryable set can still
claim an entire poll's budget and starve the pending set regardless of how it is
ordered. Do not ship these separately.
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Co-Authored-By: Claude <noreply@anthropic.com>
`retryable_notification_ids` claimed EVERY due retry with no bound, and
`deliverable_notifications` then decremented the poll budget by that count:
retryable_ids = retryable_notification_ids # unbounded
limit -= retryable_ids.size
pending_ids = limit > 0 ? pending_notification_ids(limit) : []
So whenever the due retryable set was at least `limit` deep, pending received
exactly zero for the poll. Worse, the returned batch also overshot `limit`, and
the Feeder's `batch_size - AppRunner.total_queued` short-circuit then suppressed
subsequent polls until that oversized batch drained -- extending the starvation
well past a single poll.
This is not theoretical. Measured live at Thanx with batch_size 100: a retryable
set 3,522 deep, i.e. 35x the batch size, repeatedly. Pending was receiving nothing
at all for the length of each drain.
Now pending is claimed FIRST and capped at (1 - RETRYABLE_CLAIM_SHARE) of the
budget, so it can never be starved; retryable takes the remainder plus whatever
pending left unused, so when pending is empty retries still drain at the full
batch_size and retryable is never starved either.
`retryable_notification_ids` now takes a limit and claims at most that many DUE
retries, oldest-due first. The retryable set is scored by `deliver_after.to_i`, so
ascending rank is ascending due-time; capping the claim at ZCOUNT(0, now) means
the lowest N by rank are all due, which is what makes a rank-bounded claim safe
here. ZRANGE and ZREMRANGEBYRANK inside the MULTI address an identical member set,
so nothing is ever removed without being returned.
Concurrency: with several daemon processes another may claim between the ZCOUNT
and the MULTI, in which case the removal may take a member that is not yet due
and deliver one retry earlier than its backoff intended. That is strictly less
harmful than the previous all-or-nothing race over the entire due set, and it
cannot lose a notification.
The starvation spec is direction-disagreeing: 11 due retries against a budget of
10. On the previous code it fails twice over -- the batch returns 11 (verified:
"expected: <= 10, got: 11") and the pending notification is absent.
CO-REQUISITE of the preceding priority-band commit; do not ship separately.
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Two defects in the preceding commit, both found in review. 1. `limit == 1` reserved the only slot for retries. `1 - (1 * 0.2).ceil` is 0, so `pending_notification_ids` was never called and a poll with no due retry returned NOTHING while pending work waited. limit is 1 whenever AppRunner still holds batch_size - 1 queued, so this is a reachable state, not a boundary curiosity. Pending's budget is now floored at one slot, and the slot goes to pending because pending is the latency-bearing side; retryable still receives it via `limit - pending_ids.size` when pending is empty. `deliverable_notifications` also returns early on a non-positive limit rather than relying on the callers that happen to check. 2. The rank-bounded claim could deliver a retry before its backoff elapsed. ZCOUNT-then-MULTI is two operations: another daemon claiming in between makes the rank range address a member set that no longer matches the count, and ZREMRANGEBYRANK then removes -- and this returns -- a member scoring beyond `now`. MULTI cannot fix that, because it cannot branch on the result of its own ZRANGE. ZREMRANGEBYSCORE cannot either: it would remove every due member while returning only `limit` of them, losing the rest. So the claim is now a small EVAL: ZRANGEBYSCORE ... LIMIT 0 n, then ZREM of exactly those ids. Selection and removal are one operation over one member set, which is what the previous commit's message could only describe as a caveat. The claim is still oldest-due-first, and still bounded by batch_size, which is what keeps `unpack` safe on Lua's stack. Both fixes are covered by direction-disagreeing examples: a single-slot budget with pending work and no due retry, and a due retry sharing the set with a future one (asserting both what is delivered and what stays queued). 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
…batch
Reserving a fixed share for PENDING and giving retryable the rest reads
symmetric, but it is not: the reserved share sits unused on every poll where
nothing is due to retry -- which is every poll of a large campaign drain. That
is a flat ~20% off the top of the feeder's claim rate, and the claim rate is the
binding constraint on how long a campaign takes.
Measured, on the production cluster during a campaign drain at 5 rpush tasks:
deliveries plateaued dead flat at 13,350 / 13,425 / 13,259 per minute, i.e.
2,672/min/task, against the 3,000/min that batch_size 100 over a 2s push_poll
allows. 89% of the claim ceiling, with dispatch, Aurora and Redis all well short
of theirs. (Confirmed against aws.ecs.service.running: 5 tasks through that
window, stepping to 20 at 15:10, at which point the rate immediately jumped to
43,794/min.) Giving up a fifth of that is ~10 minutes on a 2M campaign, against
a 40-minute target -- so the direction of the reservation is not a stylistic
choice.
Inverted:
* retryable claims first, CAPPED at RETRYABLE_CLAIM_SHARE of the poll, which
is what fixes the original starvation;
* pending then claims the ENTIRE remainder, so an empty retryable set costs
nothing at all;
* a second retryable pass takes whatever pending did not use, so retryable is
not starved when pending is shallow either.
Neither side starves, and no slot idles while either side has work.
Also fixes a latent off-by-one this restructure surfaced: ZRANGE bounds are
INCLUSIVE, so `pending_notification_ids(0)` did `zrange 0 0` and claimed one id
anyway -- and ZREMRANGEBYRANK removed it from the pending set to do so, so a
caller that dropped the over-budget id would have dropped the notification with
it. The old caller papered over this with its own `limit > 0 ?` ternary; the
guard now lives in the method, for every caller. Reachable in the new shape at
limit == 1 with a due retry, and pinned by an example asserting the pending
notification is still in the set afterwards.
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Co-Authored-By: Claude <noreply@anthropic.com>
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Fifteen lines above `retryable_budget` still described the ZCOUNT + MULTI + ZREMRANGEBYRANK claim, which the atomic EVAL replaced two commits ago -- including a "Concurrency note" asserting that a racing daemon can deliver a retry before its backoff elapses. That is precisely the race the EVAL eliminated, so the comment contradicted both the code beneath it and the commit message that introduced it. Orphaned mechanically: the earlier commit swapped the method body, and the next one inserted retryable_budget's own comment directly below the now-dangling block, so the stale text ended up documenting a method it never described. A wrong comment about a concurrency guarantee is worse than none -- the next reader would have designed around a race that no longer exists. Removed, and the accurate one-line description moved onto retryable_notification_ids, pointing at RETRYABLE_CLAIM_SCRIPT where the mechanism is already explained. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
rstojano
approved these changes
Sep 1, 2026
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Why
The Redis pending set is scored
zadd(pending, id, id), so delivery is strict FIFO across every app. A large campaign puts its whole fan-out ahead of every subsequent transactional push.Measured downstream at Thanx, order-status notifications took 296.7 s on average and up to 4,544 s from creation to APNs/FCM handoff, against a 120 s target — sitting behind campaign backlogs 10,000–43,363 deep for 10–15 minutes at a time, several times a week.
Two defects produce that, and both commits are required. Priority ordering alone does not fix it, because a deep retryable set can claim an entire poll's budget regardless of how the pending set is ordered.
1. Priority band (
2b7db30)Adds
priority_class(default1) and scores the pending set as:No change to the claim path.
pending_notification_idsalready claims by rank (ZRANGE 0..limit+ZREMRANGEBYRANK 0..limit), so ordering the score is sufficient to order delivery.The band is anchored on the default class, not on zero — this is load-bearing, not cosmetic. A notification at the default scores exactly its own id, so the pending set stays byte-identical to today for every existing caller. That gives: no transition window while a mixed-version fleet rolls, no score inversion between old and new writers, and a score-safe revert. A class below the default scores negative and sorts ahead of all default traffic.
|| PRIORITY_CLASS_DEFAULTrather than.to_iwhen reading the class:nil.to_iis0, which would silently promote a notification whosepriority_classfailed to load into the highest band. Falling back to the default is inert.Band is
10**12— above any plausible id, and well inside a double's exact-integer range (2**53), which matters because ZSET scores are doubles. Pinned by a spec.2.
enqueued_at+age_ms(2b7db30)Nothing in this model records creation time — there is no
created_atattribute — so the time between enqueue and handoff was simply unmeasurable. Addsenqueued_atplus anage_msreader.Stamped by a
before_createcallback, not an attribute default: Modis evaluatesdefault:once at class-definition time, sodefault: Time.nowwould brand every notification with the timestamp of process boot.age_msreturnsnilfor notifications predating the attribute (i.e. everything already resident in Redis at deploy), and callers must handle that.3. Retryable starvation (
856e7a2)retryable_notification_idsclaimed every due retry unbounded, then the poll budget was decremented by that count:Whenever the due retryable set was ≥
limitdeep, pending received exactly zero. And because the batch overshotlimit, the Feeder'sbatch_size - AppRunner.total_queuedshort-circuit then suppressed later polls until it drained — extending starvation well past one poll.Measured live with
batch_size100: a retryable set 3,522 deep — 35× the batch size, repeatedly.Pending is now claimed first and capped at
(1 - RETRYABLE_CLAIM_SHARE)of the budget; retryable takes the remainder plus whatever pending left unused, so when pending is empty retries still drain at fullbatch_size. Neither side can starve the other.Why a rank-bounded claim is safe: the retryable set is scored by
deliver_after.to_i, so ascending rank is ascending due-time. Capping the claim atZCOUNT(0, now)means the lowest N by rank are all due.ZRANGEandZREMRANGEBYRANKinside theMULTIaddress an identical member set, so nothing is removed without being returned.Concurrency caveat, stated plainly: with several daemon processes another may claim between the
ZCOUNTand theMULTI, in which case the removal may take a not-yet-due member and deliver one retry earlier than its backoff intended. That is strictly less harmful than the previous all-or-nothing race over the entire due set, and it cannot lose a notification.Testing
CLIENT=redisagainst a real Redis: 15 new examples, 0 failures.The starvation spec is direction-disagreeing — 11 due retries against a budget of 10. Verified against the previous code it fails twice over: the batch returns 11 (
expected: <= 10, got: 11) and the pending notification is absent entirely.Other discriminating anchors:
ZSCOREequals its id — the byte-identity pin for the anchored bandZSCOREequalsid - BANDpriority_classscores as default rather than being promotedenqueued_at— fails for a class-level defaultTwo pre-existing failures remain in the shared
Rpush::Daemon::Storeexamples (finds an app by ID,finds all apps). They callstore.app/store.all_apps, which this PR does not touch, and fail withActiveRecord::ConnectionNotEstablishedbecause there is no local database. Please confirm against CI.Notes for the reviewer
Gemfile.lockis deliberately not included. I ran the suite under Ruby 2.7.5 (the consuming app's version; the gemspec allows>= 2.7.0) rather than the pinned 3.1.0, which rewrites the lock. Reverted.zrangebyscore/zscoregrep is clean — the retryable namespace legitimately does, and the two are never conflated), so repurposing the pending score is safe.priority(the existing APNs/FCM delivery-priority attribute) is untouched —priority_classis a separate concept and deliberately not overloaded onto it.config.client = :redisand the AR store is never instantiated there, so adding them would require a migration for no benefit. Happy to add if you'd rather keep the two clients symmetric.Follow-up
A tag will be needed for the consuming app to pick this up. Existing thanx tags are lightweight and do not bump
Rpush::VERSIONorCHANGELOG.md; I've followed that convention by not touching either.🤖 Generated with Claude Code
Co-Authored-By: Claude noreply@anthropic.com
Summary by CodeRabbit
New Features
Bug Fixes
Tests
CI
This branch carries three commits by @rstojano, cherry-picked from the closed #10 (branch deleted; commits recovered via
refs/pull/10/head):7bad082ubuntu-22.04—ubuntu-20.04is a retired image, so jobs were never assigned a runner and sat queued indefinitely (observed 18h+, emptyrunner_name)1fb42ebsqlite3as a precompiled gem — the lockfile listed only therubyplatform, so bundler built it from source andbundle installdied before any test ran36ae319Store::Redis#all_apps/#app), while the upstream specs only create Redis apps, so every redis functional scenario timed out looking for an app that wasn't thereWithout these, CI on this repo does not run at all — which is why #13 initially showed 16 checks queued for 18 hours, then 56 failures once the runner label was fixed. Every one of those failures was pre-existing: they were
spec/functional/*and the two shared-store app-lookup examples, andretry_spec.rb:29— the only one that touches retry behaviour — failed insidelib/rpush/push.rb:7→Synchronizer#sync→apps.eachwithActiveRecord::ConnectionNotEstablished, before reaching any claim code.#10 was closed by its own author 13 seconds after his separate v9.2.0-rebase PR, with no review and no comments — abandoned rather than rejected, and it was green when closed. The skip/unskip pair from that branch (
66cb604/81918d5) is deliberately omitted: they cancel out, and36ae319applies cleanly without them.These three commits should ideally land on their own, not via this PR. They're here so the priority-band work can actually be validated by CI. Drop them if #10 is revived.