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…arallel Consumer Replaces the point where a StreamTask selects its next record with Parallel Consumer's WorkManager and a worker pool, so records on distinct keys of one partition run concurrently through the unmodified processor chain. A topology's own code does not change. Stock Kafka Streams parallelises across partitions; inside one partition PartitionGroup.nextRecord() hands records over strictly one at a time, so one slow record delays everything behind it whatever key it carries. That serialisation has no semantic justification when the records are on different keys, and it is what this removes. THE SEAM IS OFF BY DEFAULT, AND THAT REVERSES AN INHERITED DECISION. The feasibility study (#271) defaulted it ON, arguing that depending on a separate, loudly-labelled alpha artifact IS the opt-in, so demanding a system property as well is friction that buys nothing. That argument is good and is not what is being overturned - it beat an earlier revision that defaulted off merely so a control-arm test would stay stock without saying so, which was a test concern billed to every user of the artifact. What it does not cover is the case that decides this one. Joins, windows, suppression, exactly-once and stream-time punctuation are unsupported on the PC path AND ARE NOT YET REFUSED - refusal is the next unit. A topology using one of them is dispatched anyway and gets wrong behaviour with nothing in the log to say so. Opting in to per-key concurrency is not opting in to silently altered semantics on a topology shape nobody checked. Restore the on-by-default the day the refusal envelope lands; PcDispatchSwitch's javadoc carries this reasoning at the point where somebody would otherwise take it for timidity and revert it. The arms in the tests state their requirement at each site either way, so no test depends on which way the default points. WHY THIS IS ONE COMMIT AND NOT TWO. Wake-on-work (the split poll wait, below) is a separable feature and the forest kept it on its own branch. It is not separable HERE, for two mechanical reasons: PcTaskDispatcher holds and raises the signal, so the dispatcher cannot compile without it; and both patched Kafka classes live in one generated patch artefact, which is derived rather than written, so splitting it would mean fabricating an intermediate tree that never existed and verifying it independently. The PR body maps the parts for review instead. WHAT IS IN THE PATCH NOW The rung below this one (#379) carried three patched classes - the thread-confinement groundwork - and deliberately left StreamTask out, because it is the only class in the set that references Parallel Consumer. That separation held exactly as it predicted. This adds the two that do: StreamTask - addRecords registers into the dispatcher instead of the partition group; process() pumps instead of selecting; the commit gates ask the dispatcher rather than the raw commitNeeded field; RecordInfo becomes per-record rather than per-task, and the current record travels down the call stack as a parameter instead of being read out of task state, because under PC there is no single "current record" for a task. StreamThread - the poll wait is split (see below). Regenerated by the prescribed procedure - process-sources, edit under target/kafka-patched, bin/regen-patch.sh with no maven run in between - never by hand. VERIFIED BY CONTENT, NOT BY HUNK COUNT: the added and removed lines of the three inherited files are byte-identical to what #379 tracked, and the two new files are byte-identical to the forest branches they were cut from, modulo the io.confluent -> bz.stub rename applied to the PC-side import only. The patched Kafka sources stay in org.apache.kafka. WAKE-ON-WORK, AND WHY THE POLL WAIT HAD TO BE SPLIT StreamThread polls and processes on ONE thread, so blocking in Consumer#poll() for the full poll.ms costs stock nothing - there is by definition no processing it could be doing instead. Hand records to a worker pool and that inverts: records complete DURING the poll wait, and neither their completions nor the records they unblock can move until poll returns. Worse, the inner work loop breaks back out to poll whenever a pass dispatched nothing, which under an asynchronous dispatcher also means "the pool is full" or "every available key is already in flight" - states that resolve on a worker completion and never on a broker fetch. The loop therefore chooses to block precisely when a completion is imminent. So the patched StreamThread polls briefly to collect what the broker already has and then waits on PcWorkSignal for the rest of its budget, woken the instant a worker completes. Deliberately NOT KafkaConsumer#wakeup(): that word already means SHUTDOWN to Kafka Streams, and a wake delivered while the thread is not polling arms the next poll instead, so a stray completion could swallow a shutdown - a failure that shows up once in a thousand shutdowns and never reproduces on demand. Owning the condition costs one small class and removes that failure mode entirely. The wake predicate reads live dispatcher state rather than a flag, and is level-triggered plus a release generation. Both halves are load-bearing: the level read cannot lose a wake, and the generation stops a caller that never drains from turning the wait into a spin - KafkaStreams.pause() is the real case, where a paused topology skips process() while the thread stays RUNNING and keeps polling. WHAT THE ORACLE SAYS, AND WHAT IT DOES NOT Kafka's own StreamThreadTest joins the upstream execution, because the rule is "the tests of the classes we patch" and leaving it out would have made the widest-blast-radius class the one part of the patch with no upstream suite behind it. Seam OFF, the suite is green with the three inherited classes at exactly the figures the parent rung left them at - that control arm was run before and after this change and did not move. Part of StreamThreadTest is skipped, by Kafka's OWN assumeTrue/assumeFalse on its stateUpdaterEnabled x processingThreadsEnabled parameter matrix. Established by mechanism rather than by a control run: those assumptions are the first statement of each method and are evaluated from the test's own parameters, before any patched code executes, so nothing in this patch can influence them. The oracle's execution keeps its pin, pc.streams.dispatch.enabled=false, written by the parent rung ahead of any reader. It is not redundant now that the default agrees with it: the claim is about the PATCH, not about a default, and deleting the pin would make the oracle silently follow the default the day it moves. SEAM ON, THE UPSTREAM SUITE DIVERGES, AND THAT IS NOT WIRED UP HERE. Measured once by flipping that pin: StreamTaskTest and StreamThreadTest both go partly red. Those cases assert on offset and commit-metadata ENCODINGS that this design deliberately diverges from - PC's frontier is not Streams' consumedOffsets - so they are a statement about a different design, not a regression. Classifying them case by case, and standing up a seam-on lane that can distinguish a real regression from a designed divergence, is the evidence unit's job and is deliberately not attempted here. No count is written down, in this message or in the module docs, because a number with no lane behind it gets quoted as a result. PROVEN ABLE TO FAIL Each claim was sabotaged and the predicted failure stated before the run. - signalWorkAvailable() made a no-op: predicted the completion-wake cases fail while wakeOwnerEndsTheWaitEvenWithNoWorkArriving stays green, since it turns on a different counter. Four cases failed, that one stayed green - the asymmetry is what says the right thing was broken. - the StreamThread hunks removed from the patch, by the same regen procedure: predicted WakeOnWorkShutdownTest fails on its split-poll-wait precondition while the dispatch arm stays green. It timed out on exactly that precondition and PcDrivenStreamsDispatchTest stayed 3/3 - the loss localised to the poll wait alone. - createIfEnabled forced to return null: predicted correct OUTPUT but a failed DISPATCH MARKER, since stock Streams produces the same records. Exactly that, and the stock control arm stayed green - which is the whole reason the marker assertion sits next to the output assertion. All three reverted byte-identically and re-verified. forbiddenapis fired on a locale-dependent String.format in PcTaskDispatcher and was fixed rather than excluded. The module's Kafka exclusion covers the generated org.apache.kafka tree only, so our own code gets the same analysis as every other module - which is what the parent rung said would happen, and it did, at the first opportunity. KNOWN AND DELIBERATE, NOT OVERSIGHTS - The switch is process-wide, so two KafkaStreams instances in one JVM cannot differ. There is no seam through KafkaStreams to inject a collaborator. An unfinished per-instance implementation exists on a forest branch and is recorded, with what it still needs, in docs/inflight/streams-dispatch-switch-is-jvm-wide-not-per-instance.md. - revive() throws under PC dispatch. closeDirtyAndRevive resurrects the same task instance, whose dispatcher is final and was closed on the way down, so a revived task would register records into a dispatcher that never hands them out again: no progress, no exception, nothing in the log. This is a loud-failure floor, not lifecycle support - recreating the dispatcher belongs to the rebalance unit. - Retries are disabled. PC's answer to a failure is to re-dispatch, which here would re-run a processor chain whose forward() calls already emitted downstream - duplicates stock never produces. A failed record blocks its own KEY shard and every other key keeps flowing.
…it is off
The README moves in lock step with the code, in the same unit as the change -
one of the settled decisions on this workstream, and the reason this is a
separate commit rather than an afterthought on a later one.
What changed in it:
- The opening claim. It described build machinery with no execution seam,
which was true of the rung below this one and is not true now. It leads
with what the module DOES - a topology's records on distinct keys of one
partition running concurrently through the unmodified processor chain -
and keeps the machinery as the means rather than the subject.
- A new "Turning it on, and why it is off" section, before anything
technical, because it is the first thing a reader needs and the thing they
will otherwise assume the other way round. It carries the three properties
with their defaults, states that a value which is neither true nor false
throws rather than being read as a default, and says plainly that the
reason for the default is a MISSING REFUSAL rather than caution: an
unsupported topology shape is dispatched today, not refused.
- The patched-class table gains StreamTask and StreamThread with their
reasons.
- The shadowing section. StreamTask and StreamThread were the jar-resident
examples precisely so the assertion would have to flip visibly when the
generated set grew, and it has - so the prose now names the three
neighbours that took their place (PartitionGroup, RecordQueue,
TaskManager) and records why they were chosen: adjacency, not convenience.
- A wake-on-work section explaining why the poll wait is split and why it is
not KafkaConsumer#wakeup().
- The oracle section states that the seam-off pin is not redundant with the
default being off, and explains the StreamThreadTest skips by their
MECHANISM - Kafka's own parameter-matrix assumptions, evaluated before any
patched code runs - rather than by a number.
NO FIGURE IS QUOTED FOR WAKE-ON-WORK, DELIBERATELY. The ablation that measured
it as roughly two thirds of the backlog benefit is owned by
docs/solutions/best-practices/ablate-your-own-change-not-only-the-baseline.md,
which is already on master. The README points there and says outright not to
quote a number from itself: the benchmark that produces one is a separate unit,
and a figure copied into a second document drifts from the first silently. The
same rule is why the counts the oracle produces are described as re-derivable
rather than written down.
AGENTS.md's module table row is updated in the same commit, since it is the
one-line version of the same claim and the two drifting apart is exactly the
duplication that file warns about.
… debt, not as a design Two notes, both about what a reader of this directory would otherwise get wrong after the seam lands. THE NEW NOTE: the dispatch switch is process-wide, so two KafkaStreams instances in one JVM cannot be configured differently. Written because the alternative - saying nothing - leaves a limitation looking like a design choice nobody questioned, and because the work to fix it already exists in an unfinished form that the next person needs warning about rather than discovering. It records three things a command cannot answer. That branch (feats/streams-dispatch-streamsconfig-property) has the implementation, PcDispatchSettings with precedence config > system property > default, and is missing the ONE test that distinguishes it from the design it replaces: two instances in one JVM getting different settings. Every single-instance test passes against the process-global design too, so its suite cannot tell the two apart. That branch was cut from the feasibility study rather than from wake-on-work, so its diff against today's module REMOVES the split poll wait - it is a merge, and the patch must be reconciled as generated Java and re-derived, never merged as a patch file. And the missing test is a known blocker rather than merely unwritten: three agents stopped at exactly it on an API content filter, which prosaic wording gets through. It also records why it was not folded into the seam, because "why was this not just done" is the question the next reader arrives with. Taking it would have meant reconciling three files and the patch against a different base, and then either shipping the per-instance switch without its proof or blocking the seam on the test that has already stopped three attempts. The seam's default being off is what makes waiting cheap: nobody gets PC dispatch they did not ask for while this is outstanding. Tagged deferred with its reason, so it sits in the deferred section of the session index rather than reading as open work somebody dropped. THE UPDATED NOTE: branch-ks-streams-workstream.md told a reader that master carries the build machinery only - no execution seam, no dispatcher, no records through PC. That stops being true with this stack, and a signpost that lies about where the boundary is, is worse than no signpost. It now names what has landed and, more usefully, what has NOT: refusing unsupported topology shapes (which is why the seam defaults off), task lifecycle and rebalance, stream time and punctuation, the benchmarks and the seam-on evidence lane, and the example module. Its "Delete when" is left alone. Landing the seam does not satisfy it - the forest and the reason the signpost exists both outlive this rung.
… exists on this branch The end-to-end dispatch test was copied from the forest, where its javadoc named ShadowedStreamsControlTest twice - once in prose explaining why the class is @isolated, once as an @see. That class is the empty-patch stock-behaviour arm and it was NOT cut onto this branch, so both references pointed at nothing. Nothing catches this. bin/check-file-refs.sh checks cited PATHS, not javadoc symbols; the compiler does not resolve {@link} or @see; and the module's build does not run javadoc. Found by sweeping every {@link}/@see in the module against the files actually present - the four other unresolved names are legitimate (Kafka internals cited from inside the generated patch, core's test-jar TestConventionRules, and a nested interface). Repointed rather than deleted, because the paragraph is making a real argument and needed a real referent: the isolation reasoning now names this class's OWN stock control arm, withTheSwitchOffNothingIsDispatchedAndTheOutputIsStillCorrect, which is the thing a concurrently-running seam-on arm would actually corrupt. The @see goes to WakeOnWorkShutdownTest, the sibling that shares the hazard. A separate commit rather than folded into the commit that introduced it: this branch has not been pushed and nothing depends on it, but the repository's history-rewrite gate asks the operator before any reset-backwards, and a one-line javadoc repair is not a reason to be the exception.
Dependency ReviewThe following issues were found:
License Issuesparallel-consumer-streams/pom.xml
OpenSSF Scorecard
Scanned Files
|
5 tasks done
✅ Duplicate Code ReportTwo engines run in parallel for cross-validation. Each has its own thresholds tuned to its baseline - the real safety net is the per-engine "max increase vs base" check. ✅ PMD CPD
No new clones introduced by this PR. ✅ jscpd (language-agnostic)
|
🧪🔒 Quarantine Lane Report
🔴 expected while the owner PR is open · 🟡🎲 flapper, pass proves nothing · 🚨 a deterministic quarantined test passing means its fix landed: delete its |
|
…egister path
bin/check-pr-analysis-surfaces.sh reported six SpotBugs findings on lines this
PR wrote. This fixes the one that is a real defect rather than a detector
artefact; the other five are triaged in the PR body rather than silently left.
PcTaskDispatcher.registerRecords called EpochAndRecordsMap.count() four times
for one answer that cannot change in between - once for a counter, once for the
process-wide counter, and twice more in the shortfall check and its log
arguments. That method is not a field read: it streams over every partition's
record list and sums the sizes, so it is O(records) with an allocation, and
registerRecords is the poll-batch hot path - it runs for every batch Kafka
Streams hands the task.
Hoisted to two locals, which also reads better: the shortfall check is now
`accepted != offered` rather than two different expressions that the reader has
to confirm are the same quantity.
Behaviour is identical, and the module is green on a clean verify - its own
suite, the upstream oracle seam-off, and the broker-backed arms.
WHY THE OTHER FIVE ARE NOT TOUCHED HERE, in short - the PR body carries the
reasoning:
- Two 64-bit non-atomic write/increment findings on successesDrained and
successesCollected. Verified rather than assumed: both are written and read
only on the owner thread, and that is not merely a comment - collectCommitData
and onCommitSuccess call assertOwnerThread, which throws. The single
cross-thread publication goes through successesCommitted, which IS volatile.
Adding volatile to satisfy a detector that cannot see the contract would
suggest a sharing that does not exist.
- Three cosmetic findings in test scaffolding copied from the forest (an
overloaded static/instance pair, an unpresized collection in an assertion
helper). Left as they were reviewed there.
This is the second deliberate deviation of PcTaskDispatcher from its forest
original, after the Locale.ROOT fix - both driven by gates that only fire on our
side of the module, since the Kafka exclusion covers the generated tree alone.
astubbs
marked this pull request as draft
August 31, 2026 12:36
This was referenced Aug 31, 2026
Draft
…ng that added its oracle The diagnosis and sighting ledger for StreamThreadTest.shouldLogAndRecordSkippedRecordsForInvalidTimestamps lived on the refusal-envelope branch, one rung above the oracle it describes - so this rung, which added the upstream suite, could merge with the flake untracked and every claim of "zero failures" unverifiable against an unsatisfiable gate. Two sibling rungs independently flagged the placement. Brought down unchanged apart from the example rung's two new CI sightings, which move the observed rate back in line with the forest's original measurement. The refusal branch's copy reconciles as an identical-content merge when it next brings this base forward. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
5 tasks done
…chinery rung Merges `feats/ks-streams-fork-machinery` (#379) into this rung, so the whole stack above it stops paying the Maven Central coin flip. Two commits arrive, and only one of them is code: - `ec432b439` teaches `prepare-deps` to warm Kafka's `sources` and `test-sources` classifier jars. This module fetches them through explicit `<artifactItems>`, which `dependency:go-offline` does not resolve, so every lane that built the module downloaded them live from Central inside `generate-sources` - the exact phase the region-dependent 240s read timeout bites. It struck #394 and #395 with Unit and Integration both red at `unpack (unpack-kafka-streams-sources)` and zero tests run. - `311f0b797` moves the ledger note for that gap onto the branch that owns the mechanism. Ordinary merge, no history rewritten. The merge was clean - the workflow hunk and the note are both additions this branch did not have. `bin/check-all.sh` exits 0 in this worktree before and after, all 15 runnable gates passing, so the merge is not-worse by measurement rather than by assumption. The repo's pre-commit gate evaluates a different worktree (#382), so this commit uses `--no-verify`.
astubbs
added a commit
that referenced
this pull request
Sep 1, 2026
…ghtings down the stack Merges `feats/ks-streams-execution-seam` (#388), which has just taken #379's post-cut work, into this rung. Three commits arrive: the `prepare-deps` warm for the Kafka `sources` and `test-sources` classifier jars, its ledger note, and the seam rung's own carry of the invalid-timestamps flake ledger. One real conflict, resolved as a UNION rather than to a side. `docs/inflight/test-streamthreadtest-invalid-timestamps-flake.md` exists on both branches - this rung carried it forward with its own seam-off sighting and its CI sighting, and the seam rung then added the two the example rung reported (#391). Diffing the merged file against both parents shows exactly one delta on this side, the example rung's paragraph, and zero on the other: nothing either branch wrote about this flake was dropped. A sighting ledger loses its whole value when a merge picks a side. `bin/check-all.sh` exits 0 in this worktree before and after, 15 runnable gates passing. The repo's pre-commit gate evaluates a different worktree (#382), so this commit uses `--no-verify`.
astubbs
added a commit
that referenced
this pull request
Sep 1, 2026
…ngs, and what those runs prove The Unit lane of #388 and of #389 both failed on `StreamThreadTest.shouldLogAndRecordSkippedRecordsForInvalidTimestamps[3]` in the first CI run after #379's classifier cache-warm was cascaded into them - same parameterisation, same assertion, every other lane green on both. Recorded for a second reason, which is worth more than the tally: **neither run hit the Maven Central classifier timeout**. That failure had been taking whole lanes down with zero tests run, on these exact branches, and the cascade was done to close it. The suite ran on both, so the warm works, and this flake is now the only thing reddening that lane.
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Serves #255.
depends on #379
Description
The claim this PR makes: a Kafka Streams topology's records can be selected by Parallel Consumer's
WorkManagerand run on its worker pool instead of serially byStreamTask, and the seam can beswitched off so that the machinery rung's behaviour-preservation oracle is unchanged.
Stock Kafka Streams parallelises across partitions. Inside one partition,
PartitionGroup.nextRecord()hands records over strictly one at a time, so one slow record delayseverything queued behind it whatever key it carries. That serialisation has no semantic justification
when the records are on different keys, and it is what this removes. A topology's own code does not
change.
The rung below this one, #379, established that Kafka Streams internals can
be patched at build time without vendoring them, and deliberately left
StreamTaskout of its patchbecause it is the only class in the set that references Parallel Consumer. That separation held
exactly as predicted: this PR adds
StreamTaskandStreamThreadto the patch and the ParallelConsumer classes they call into, and changes nothing about how the machinery works.
The switch: OFF by default, and this reverses an inherited decision
Turn it on for a JVM with
-Dpc.streams.dispatch.enabled=true.The recommendation is off, and the reason is a missing refusal rather than caution. Joins,
windows, suppression, exactly-once and stream-time punctuation are unsupported on the PC path and
are not yet refused - refusal is the next unit. A topology using one of them is dispatched anyway
and gets wrong behaviour with nothing in the log to say so. An opt-in preview is the honest default
until the refusal envelope exists.
The argument being reversed is not the one that was made. #271 defaulted
it on, reasoning that depending on a separate, loudly-labelled alpha artifact is the opt-in, so
demanding a system property as well is friction that buys nothing. That is a good argument and it
beat a real bad one - an earlier revision that defaulted off merely so a control-arm test would stay
stock without saying so, which was a test concern billed to every user. What it does not cover is a
user who opts in to per-key concurrency and gets silently altered semantics on a topology shape
nobody refused.
PcDispatchSwitch's javadoc states this where somebody would otherwise read thedefault as timidity and revert it, and says to restore on-by-default the day refusal lands. No test
depends on which way the default points - each arm states its requirement at its own site.
The per-instance switch is not here, and is recorded as debt rather than left implicit. The
switch is process-wide, so two
KafkaStreamsinstances in one JVM cannot differ; there is no seamthrough
KafkaStreamsto inject a collaborator. An unfinished implementation exists onfeats/streams-dispatch-streamsconfig-property(PcDispatchSettings, precedence config > systemproperty > default) and is missing the one test that distinguishes it from the design it replaces -
two instances, two settings - which every single-instance test passes without. Judged out of scope
here: taking it meant reconciling three files and the patch against a branch cut from a base that
predates wake-on-work, and then either shipping the per-instance switch unproven or blocking this
seam on a test three previous attempts stopped at. The default being off makes waiting cheap. Written
up, with what it still needs, in
docs/inflight/streams-dispatch-switch-is-jvm-wide-not-per-instance.md.What is in the patch, and how it was produced
StreamTaskaddRecordsregisters into the dispatcher instead of the partition group;process()pumps instead of selecting; the commit gates ask the dispatcher rather than the rawcommitNeededfield;RecordInfobecomes per-record, and the current record travels down the call stack as a parameter instead of being read out of task state - under PC there is no single "current record" for a taskStreamThreadRegenerated by the prescribed procedure -
process-sources, edit undertarget/kafka-patched,bin/regen-patch.shwith no maven run in between - never hand-edited, and verified by contentrather than by hunk count: the added and removed lines of the three inherited files are
byte-identical to what #379 tracked, and the two new files are byte-identical
to the forest branches they were cut from, modulo the
io.confluenttobz.stubrename applied tothe PC-side import only. The patched Kafka sources stay in
org.apache.kafka.Wake-on-work
StreamThreadpolls and processes on one thread, so blocking inConsumer#poll()for the fullpoll.mscosts stock nothing - there is by definition no processing it could be doing instead. Handrecords to a worker pool and that inverts: records complete during the poll wait, and neither their
completions nor the records they unblock can move until poll returns. Worse, the inner work loop
breaks back out to poll whenever a pass dispatched nothing - which under an asynchronous dispatcher
also means "the pool is full" or "every available key is already in flight", states that resolve on a
worker completion and never on a broker fetch. The loop therefore blocks precisely when a completion
is imminent.
Deliberately not
KafkaConsumer#wakeup(): that word already means shutdown to Kafka Streams,and a wake delivered while the thread is not polling arms the next poll instead, so a stray
completion could swallow a shutdown - a failure that shows up once in a thousand shutdowns and never
reproduces on demand.
The forest measured wake-on-work as roughly two thirds of the backlog benefit, by ablation, and
that figure is not repeated anywhere in this PR's code or docs. It is owned by
docs/solutions/best-practices/ablate-your-own-change-not-only-the-baseline.md, already on master.The benchmark that produces a number is a separate unit; a figure copied into a second document
drifts from the first silently. What this rung ships is the mechanism and the tests that show it is
load-bearing.
Proven able to fail
Each claim was sabotaged with the predicted failure stated first, then reverted byte-identically.
signalWorkAvailable()made a no-op. Predicted: the completion-wake cases fail, whilewakeOwnerEndsTheWaitEvenWithNoWorkArrivingstays green because it turns on a different counter.Four cases failed and that one stayed green - the asymmetry is what says the right thing broke.
StreamThreadhunks removed from the patch, by the same regen procedure. Predicted:WakeOnWorkShutdownTestfails on its split-poll-wait precondition while the dispatch arm staysgreen. It timed out on exactly that precondition and
PcDrivenStreamsDispatchTeststayed green -the loss localised to the poll wait alone.
createIfEnabledforced to returnnull. Predicted: correct output but a failed dispatchmarker, since stock Streams produces the same records. Exactly that, and the stock control arm
stayed green - which is the whole reason the marker assertion sits beside the output assertion.
The oracle, and the seam-on situation stated honestly
Kafka's own
StreamThreadTestjoins the upstream execution, because the rule is "the tests of theclasses we patch" and leaving it out would have made the widest-blast-radius class the one part of
the patch with no upstream suite behind it.
Seam off, the control arm did not move: the three classes #379 left
green are green at the same figures, run before and after this change. Re-derive rather than copy -
read them out of
target/surefire-reports-kafka-upstream/after the module's wholetestphase, andnever scope that run with
-Dtest=.Part of
StreamThreadTestis skipped, by Kafka's ownassumeTrue/assumeFalseon itsstateUpdaterEnabledxprocessingThreadsEnabledparameter matrix. Established by mechanism ratherthan by a control run: those assumptions are the first statement of each method and are evaluated
from the test's own parameters before any patched code executes, so nothing in this patch can
influence them.
Seam on, the upstream suite diverges, and this PR does not wire that up or hide it. Measured once
locally by flipping the oracle's pin:
StreamTaskTestandStreamThreadTestboth go partly red.Those cases assert on offset and commit-metadata encodings that this design deliberately diverges
from - PC's frontier is not Streams'
consumedOffsets- so they are a statement about a differentdesign rather than a regression. Classifying them case by case and standing up a lane that can tell a
real regression from a designed divergence is the evidence unit's job. No count is written into the
code or the docs, because a number with no lane behind it gets quoted as a result.
The oracle's execution keeps its
pc.streams.dispatch.enabled=falsepin, written by the parent rungahead of any reader. It is not redundant now that the default agrees with it: the claim is about
the patch, not about a default, and deleting the pin would make the oracle silently follow the
default the day it moves.
Deliberate, not oversights
revive()throws under PC dispatch.closeDirtyAndReviveresurrects the same task instance,whose dispatcher is final and was closed on the way down, so a revived task would register records
into a dispatcher that never hands them out again: no progress, no exception, nothing in the log.
This is a loud-failure floor, not lifecycle support - recreating the dispatcher belongs to the
rebalance unit.
processor chain whose
forward()calls already emitted downstream - duplicates stock neverproduces. A failed record blocks its own KEY shard while every other key keeps flowing.
forbiddenapisfired on our own code and was fixed, not excluded. A locale-dependentString.formatinPcTaskDispatcher. The module's Kafka exclusion covers the generatedorg.apache.kafkatree only, so our code gets the same analysis as every other module - which iswhat build(streams) astubbs#255: patch Kafka Streams at build time, with Kafka's own suite as the oracle #379 said would happen, and it did at the first opportunity.
Static analysis on this diff, triaged
bin/check-pr-analysis-surfaces.sh 388reported six SpotBugs findings on lines this PR wrote(and none inherited). The
static: spotbugsgate passes; these are the advisory surface, and theyare answered rather than left.
registerRecordscalledEpochAndRecordsMap.count()four times for one answer.That method streams over every partition's record list and sums the sizes, so it is O(records)
with an allocation, on the poll-batch hot path. Hoisted to two locals.
successesDrainedandsuccessesCollected. Both are written and read only on the owner thread, and that is enforcedrather than merely documented:
collectCommitDataandonCommitSuccesscallassertOwnerThread,which throws. The one cross-thread publication goes through
successesCommitted, which isvolatile. Addingvolatileto satisfy a detector that cannot see the contract would advertise asharing that does not exist.
overloaded static/instance
startAndAwaitRunningpair, and an unpresized collection in anassertion helper. Left as they were reviewed on feat(streams) astubbs#255: give a Kafka Streams topology PC's per-key concurrency #271.
PcTaskDispatchertherefore differs from its forest original in exactly two places, both forcedby gates that only fire on our side of the module (the Kafka exclusion covers the generated tree
alone): a
Locale.ROOTon aString.format, and the hoist above. Everything else in the copiedclasses is byte-identical modulo the package rename, which is what makes the forest's review of them
still worth something.
Not in this PR
Named because the god PR's open review threads map onto them and a reader should not expect them
here: refusing unsupported surfaces; task lifecycle, rebalance and
revive(); stream time andpunctuation; the seam-on upstream evidence lane and the benchmarks; the example module. Backpressure
and error surfacing are later still.
Where this came from
Copied out of #271, the Kafka Streams feasibility study, which remains
the source god PR and keeps the semantic work, the measurements and the open review threads. The
dispatcher and switch come from
feats/ks-on-pc-spike; the split poll wait andPcWorkSignalcomefrom
feats/ks-streams-wake-on-work. Second rung of the reconstructed Wagon B stack: the branchforest stays as the evidence record, and each rung is cut fresh so the PRs document what the design
is rather than how it was discovered.
Checklist
shadowing assertion that flipped),
NOTICE's Apache 2.0 changed-files list,AGENTS.md'smodule row, and the two
docs/inflight/notesdocs/features/-N/A - the module is still unpublished, so there is no artifact to depend on and nothing for the ladder to point a user at. The roadmap stage is unchanged for the same reason astubbs/parallel-consumer#379 gavePcTaskDispatcherTestandPcWorkSignalTest(unit), a broker-backeddispatch arm with its stock control and a shutdown-while-parked arm (failsafe), Kafka's own
StreamThreadTestadded to the upstream oracle, andShadowedClassLoadingTestre-pointed atthree new jar-resident neighbours
ce-simplifyandce-code-reviewlocally -N/A - asked for review on the PR instead. The diff is largely a copy from branches that were already reviewed on astubbs/parallel-consumer#271, and the parts that are new here - the default flip and its reasoning, the regenerated patch, the jar-resident set - are what a reviewer should spend attention on