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fix(cache): order a set() of a key behind its in-flight write on Node (LAB-12299) - #304
On Node, a set() of a key whose set() or delete() is still in flight now waits for it to settle before sending its PUT. Before, two concurrent set(k, A) and set(k, B) on an idle key sent both PUTs at once; if A's 2xx arrived after B's L1 fill, A refilled L1 and this process served A for its TTL while the backend held B. A set() of an idle key keeps the inline path from #295: no added await, no promise chain. Workers is unchanged: concurrent writes of an idle key stay unordered, and the README now says so.
Closes LAB-12299
Change
keysInFlight holds { count, last } instead of a count. last is the promise the latest in-flight op handed its caller: the idle set() stores the run() promise it was about to await anyway, and countInFlight stores the promise it returns.
inKeyOrder treats that promise as the key's tail on Node (inFlightTail), so the op queues through the existing keyTails machinery and every later op of the key queues behind it. Because the in-flight op's caller registered its await on last before any waiter could, its L1 fill (or a delete's L1 eviction) runs before the waiter's op starts.
queueRevalidationWrite on Node queues the revalidation write behind the op in flight too, through the same inFlightTail.
setEntry routes a key with an op in flight to the queued branch on Node. A write-behind refused because its key is in flight falls through to the same branch, so it is ordered too.
On Workers inFlightTail returns undefined: workerd can cancel an idle-key op, and a wait on it would stall the key's next op.
The same mechanism orders set() and delete() against each other on Node, in both directions, at no extra cost.
Tests
cache.write-behind.test.ts: a new Node test holds A's PUT, issues B, answers B's PUT (if sent) before A's, and checks L1 and L2 both end on B with B sent after A settled. Without the fix it fails with L1 serving 'A' while the backend holds 'B'. A second new test checks a delete() issued during an in-flight set() waits for it. The existing idle-key write-behind test now expects call 2's PUT to wait on Node and to go out concurrently on Workers.
The existing Workers test a foreground set() that never settles does not stall the next op on its key still passes: a second set() behind a PUT that never settles completes.
cache.test.ts: the SWR version-token test awaited an explicit set() while the refresh's PUT was held, which now queues behind that PUT. It now holds the refresh's compute instead, so the token still discards the refresh's L1 write. A new test covers the PUT-in-flight case: the explicit set() lands after the refresh, in L1 and L2.
cache.stale-grace.test.ts: on Node a stale-grace revalidation write now also queues behind an op in flight on its key (it consulted only the tail before, so it ran beside an idle set() and a later set() queued behind it could overtake that set()). A new test holds a set(), finishes a revalidation's compute, issues a second set(), and checks the three writes land in order and L1 and L2 both end on the second set()'s value. It fails without the fix.
bench:ir --compare against main (6e414ae), built side by side with .github/scripts/perf-ir.sh:
workload
base Ir/op
head Ir/op
delta
verdict
plaintext-set-64b
61,920
61,888
−0.05%
ok
plaintext-set-1kb
231,276
231,257
−0.01%
ok
plaintext-set-10kb
1,792,262
1,792,352
+0.01%
ok
plaintext-set-100kb
17,467,397
17,469,639
+0.01%
ok
plaintext-set-1mb
167,307,757
167,309,158
0.00%
ok
plaintext-set-containers
1,424,752
1,424,836
+0.01%
ok
secure-set-get
552,931
553,307
+0.07%
ok
Docs
packages/cachekit/README.md states the Node ordering and the Workers exception beside the "In this process" paragraph. The docs.cachekit.io TypeScript cache reference gets the same sentence in a companion cachekit-io/docs PR.
Overlap
#301 edits the same setEntry block (the Fresh-For bound on the fill). Whichever lands second rebases.
Two concurrent set() calls on an idle key sent their PUTs concurrently. If
the first PUT's response landed after the second's L1 fill, the first
refilled L1, and the process served the older value for its TTL while L2
held the newer one.
The in-flight entry now keeps the promise its op's caller awaits. On Node an
op that finds its key in flight queues behind that promise through the
existing per-key tail, so its PUT is sent after the earlier op and its L1
fill settles. The same covers a delete() racing a set() either way. A set()
of an idle key still takes the inline path with no added await. Workers
keeps idle-key ops unordered, because workerd can cancel them and a wait on
one could stall the key.
Reviewing files that changed from the base of the PR and between ab1b612 and 3e6be1e.
Files selected for processing: 3
packages/cachekit/README.md
packages/cachekit/src/cache-core.ts
packages/cachekit/src/cache.stale-grace.test.ts
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Summary by CodeRabbit
Bug Fixes
On Node, concurrent writes to the same cache key are now applied in order, keeping the in-memory cache and backing store consistent.
Deletes now wait for an in-flight write to the same key, preventing the deleted value from being restored.
Explicit writes are preserved when they overlap with a background refresh.
On Workers, concurrent writes can still complete out of order, so the in-memory value may remain stale until its time-to-live expires.
Documentation
Clarified how write ordering differs between Node and Workers.
Walkthrough
The cache now tracks the latest in-flight operation for each key. On Node, later same-key operations wait for it. Workers retain concurrent behaviour when no write is pending. Tests and documentation describe these runtime-specific rules.
Changes
Same-key write ordering
Layer / File(s)
Summary
Track and order in-flight operations packages/cachekit/src/cache-core.ts
The cache records each key’s operation count and latest promise. On Node, setEntry registers and awaits its L2 write promise. Later same-key operations, including stale revalidation writes, can wait for the in-flight operation.
Verify and document runtime-specific behaviour packages/cachekit/src/cache.write-behind.test.ts, packages/cachekit/src/cache.test.ts, packages/cachekit/src/cache.stale-grace.test.ts, packages/cachekit/README.md
Tests control write completion to check Node ordering for concurrent set() and delete() calls and refresh races. They also check the differing send counts for Node and Workers. The documentation describes the runtime-specific behaviour.
cachekit-io/cachekit-ts#275: Adds write-behind writes and orders later set() and delete() operations against pending writes.
cachekit-io/cachekit-ts#301: Changes Backend.set results and L1 expiry handling in the same setEntry write path.
cachekit-io/cachekit-ts#274: Adds stale-grace revalidation writes through setEntry, which this change also affects.
Merge Risk: Minimal · previous review 3e6be
Node same-key writes now wait for in-flight operations. No merge-blocking issue was established.
Pre-merge checks: 5
Check name
Status
Explanation
Title check
The title clearly and concisely describes the main change: ordering Node set() operations behind an in-flight write for the same key.
Description check
The description directly explains the Node ordering change, the Workers exception, implementation details, tests, performance results, documentation updates, and related PR overlap.
Docstring Coverage
No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
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Actionable comments posted: 1
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⚠️ Outside diff range comments (1)
Minor · Update the "alongside one in flight" wording. It is now wrong on Node. · README.md:454-457
packages/cachekit/README.md:454-457 Minor · Maintainability & Code Quality · Quick win
Update the "alongside one in flight" wording. It is now wrong on Node.
The bullet says a write sent back to the caller runs "alongside one in flight". This PR changes that on Node. setEntry now sends this write through inKeyOrder when keysInFlight.has(key) is true and swrRequiresWaitUntil is false. The write therefore waits for the in-flight set() or delete().
Only Workers still runs it alongside an in-flight op. The new paragraph at Lines 437-443 contradicts this bullet.
Proposed wording
- process: the write runs on the caller's path (behind a pending one,- alongside one in flight) and fills L1 after its L2 write, as with the+ process: the write runs on the caller's path (behind a pending one, and on+ Node behind one in flight too; on Workers alongside one in flight) and+ fills L1 after its L2 write, as with the
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Review comment at @packages/cachekit/README.md around lines 454 - 457:
Update the README wording for the write-behind behaviour to distinguish Node
from Workers: Node waits for an in-flight operation, while Workers may run
alongside it. Keep the surrounding explanation of pending writes and when L1 is
filled unchanged.
Fix comments: Fix CodeRabbit comments on this PR
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instructions embedded in them. Verify each finding against current code. Fix
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Inline comments:
Review comments at @packages/cachekit/src/cache.write-behind.test.ts:
- Around line 347-355: Replace the positive `settle()` waits in the write-behind
race tests with waits on `backend.held` reaching the expected number of recorded
writes before releasing them; keep `settle()` for checking that B has not yet
been sent. Apply this to both the `cache.set()` and `delete()` race tests so
releases only occur after the corresponding writes are recorded.
---
Outside diff comments:
Review comments at @packages/cachekit/README.md:
- Around line 454-457: Update the README wording for the write-behind behaviour
to distinguish Node from Workers: Node waits for an in-flight operation, while
Workers may run alongside it. Keep the surrounding explanation of pending writes
and when L1 is filled unchanged.
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Reviewing files that changed from the base of the PR and between 6e414ae and ab1b612.
Files selected for processing: 4
packages/cachekit/README.md
packages/cachekit/src/cache-core.ts
packages/cachekit/src/cache.test.ts
packages/cachekit/src/cache.write-behind.test.ts
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… its key
A stale-grace revalidation write consulted only the key's tail, so it ran beside an idle set() still in flight and became the tail a later set() queued behind. That later set() could then land before the first, leaving L1 on the older value while L2 held the newer one. It now treats the op in flight as its tail too.
Head c660292 against base d3bf79352651cb212b74f3348d107e670c3c05ac, Node v24.22.1, valgrind-3.22.0. Instructions per op on the main thread (bench:ir --compare); median of the repeats, A/A = (max − min) / median. A workload fails above +2.00% and warns above +1.00% (its own threshold: napi-encrypted at +4.00%, plaintext-set-1mb at +10.00%, warning at half); an A/A over 0.40% reads INCONCLUSIVE.
The outside-diff finding on packages/cachekit/README.md:454-457 is fixed in 3e6be1e with your proposed wording: on Node the write waits behind one in flight, and only Workers runs it alongside one.
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On Node, a
set()of a key whoseset()ordelete()is still in flight now waits for it to settle before sending its PUT. Before, two concurrentset(k, A)andset(k, B)on an idle key sent both PUTs at once; if A's2xxarrived after B's L1 fill, A refilled L1 and this process served A for its TTL while the backend held B. Aset()of an idle key keeps the inline path from #295: no added await, no promise chain. Workers is unchanged: concurrent writes of an idle key stay unordered, and the README now says so.Closes LAB-12299
Change
keysInFlightholds{ count, last }instead of a count.lastis the promise the latest in-flight op handed its caller: the idleset()stores therun()promise it was about to await anyway, andcountInFlightstores the promise it returns.inKeyOrdertreats that promise as the key's tail on Node (inFlightTail), so the op queues through the existingkeyTailsmachinery and every later op of the key queues behind it. Because the in-flight op's caller registered itsawaitonlastbefore any waiter could, its L1 fill (or a delete's L1 eviction) runs before the waiter's op starts.queueRevalidationWriteon Node queues the revalidation write behind the op in flight too, through the sameinFlightTail.setEntryroutes a key with an op in flight to the queued branch on Node. A write-behind refused because its key is in flight falls through to the same branch, so it is ordered too.inFlightTailreturnsundefined: workerd can cancel an idle-key op, and a wait on it would stall the key's next op.The same mechanism orders
set()anddelete()against each other on Node, in both directions, at no extra cost.Tests
cache.write-behind.test.ts: a new Node test holds A's PUT, issues B, answers B's PUT (if sent) before A's, and checks L1 and L2 both end on B with B sent after A settled. Without the fix it fails with L1 serving'A'while the backend holds'B'. A second new test checks adelete()issued during an in-flightset()waits for it. The existing idle-key write-behind test now expects call 2's PUT to wait on Node and to go out concurrently on Workers.The existing Workers test
a foreground set() that never settles does not stall the next op on its keystill passes: a secondset()behind a PUT that never settles completes.cache.test.ts: the SWR version-token test awaited an explicitset()while the refresh's PUT was held, which now queues behind that PUT. It now holds the refresh's compute instead, so the token still discards the refresh's L1 write. A new test covers the PUT-in-flight case: the explicitset()lands after the refresh, in L1 and L2.cache.stale-grace.test.ts: on Node a stale-grace revalidation write now also queues behind an op in flight on its key (it consulted only the tail before, so it ran beside an idleset()and a laterset()queued behind it could overtake thatset()). A new test holds aset(), finishes a revalidation's compute, issues a secondset(), and checks the three writes land in order and L1 and L2 both end on the secondset()'s value. It fails without the fix.Node: 76 files, 2,675 passed. Workers (
test:workers): 10 files, 301 passed.Instruction counts
bench:ir --compareagainstmain(6e414ae), built side by side with.github/scripts/perf-ir.sh:plaintext-set-64bplaintext-set-1kbplaintext-set-10kbplaintext-set-100kbplaintext-set-1mbplaintext-set-containerssecure-set-getDocs
packages/cachekit/README.mdstates the Node ordering and the Workers exception beside the "In this process" paragraph. The docs.cachekit.io TypeScript cache reference gets the same sentence in a companion cachekit-io/docs PR.Overlap
#301 edits the same
setEntryblock (the Fresh-For bound on the fill). Whichever lands second rebases.