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fix: keep short rotation quarters as selected - #8074
Rotating LLMQs (DIP0024) are built from four quarters, one per DKG cycle. When a cycle can't fill a quarter because too few eligible masternodes are left outside that quorum index's previous three quarters, the builder correctly selects fewer members. But neither legacy snapshot mode records quarter lengths, so when later cycles rebuild that quarter from its snapshot, GetQuorumQuarterMembersBySnapshot fills it up to quarterSize by continuing around the candidate list. That adds members that were never selected, and they can repeat members of the quorum's other quarters. Separately, the builder's early returns store no snapshot at all, and a missing snapshot makes later cycles stop loading their older quarters.
In regtest with 3 masternodes this produces compositions like [4a61 | 4a61 | 4a61 | dd15]. The DKG maps a proTxHash to a single member index, so a repeated masternode's extra slots never record a contribution; they are treated as non-contributing members, which leads to complaints and PoSe penalties for an honest masternode. This is what made feature_llmq_dkgerrors.py fail intermittently.
This is the ungated alternative to #8012: no deployment, the new rules apply to every cycle, and the few testnet cycles whose history differs keep the legacy rules. It deliberately changes only what can't break mainnet: candidates are ordered and accepted exactly as before, so the new walk selects differently only where the legacy walk stopped early (short or empty quarters, too few enabled masternodes).
Not fixed here: when the builder collects previous members into CDeterministicMNLists with AddMN, unique-property conflicts between historical member states (e.g. an address reused after service updates) throw and are silently swallowed, so a member can drop out of its index's exclusion set and be selected again ([A, B, A]), even with many eligible masternodes. Mainnet history also depends on these AddMN conflicts (they reorder candidates at cycle 1800288 and block one at cycle 1878912), so excluding by proTxHash would need a gated change; #8012 does that.
What was done?
refactor(llmq): the existing selection and rebuild loops move unchanged into WalkLegacyQuarters / ReplayLegacyQuarters, with tests pinning their output, including the skip-list quirk where a first skip at position 0 is treated as unset, and the serialized snapshot bytes.
feat(llmq): WalkNewQuarters / ReplayNewQuarters, a walk that records skips as step numbers (first absolute, then positive deltas) and ends a quarter when full or after list.size() consecutive skips, so its replay reproduces exactly what was selected, including short and empty quarters.
feat: a regtest-only -llmqtestdip0024params=<size>:<threshold> that sets the LLMQ_TEST_DIP0024 size and sets minSize, threshold and dkgBadVotesThreshold to <threshold>; the size must be a positive multiple of 4 within the supported maximum.
feat(llmq): a new snapshot mode, MODE_SHORT_QUARTERS (4), for cycles with a short or empty quarter, whose skip list holds walk steps. Snapshots are now decoded by their mode: modes 0 and 1 keep the legacy replay byte for byte. LegacySkipListForWalk gives the skip list the legacy builder stores for a step walk whose quarters are all full, which is the same walk.
fix(llmq), the consensus change:
every cycle's new quarters are built with the step walk, and every successful build stores a snapshot, including cycles with short or empty quarters or no eligible masternodes (no early returns), except the testnet cycles that keep the legacy walk;
candidates are ordered and accepted exactly as before, AddMN conflicts included. Where every quarter fills, the step walk therefore selects what the legacy walk would have, and the snapshot stores exactly the legacy bytes, so the cycle is rebuilt as before, including after the walk wraps around the candidate list, where the legacy replay doesn't always rebuild what was built;
only a cycle with a short or empty quarter, or with too few enabled masternodes, is stored in MODE_SHORT_QUARTERS and rebuilt as it was selected, so clients that only know the legacy modes keep working until such a cycle occurs;
testnet's history has 12 cycles where the step walk selects differently: too few masternodes at h=838368, short quarters at h=901152-903168 and h=1366560-1367136. Their base block hashes are listed in a new consensus parameter, llmqLegacyRotationCycles, and those cycles keep the legacy walk.
test: DashTestFramework gains a configurable rotating-quorum minimum size and optional "predictions must be known" checks; feature_llmq_rotation.py now requires known predictions.
test: new feature_llmq_rotation_short_quarters.py.
doc: release note, including the MODE_SHORT_QUARTERS decoding rule for SPV clients.
How Has This Been Tested?
Tested on macOS (Apple Silicon), depends build, configured with --enable-debug --enable-werror --enable-crash-hooks.
Unit tests (src/test/llmq_utils_tests.cpp, llmq_params_tests.cpp), full test_dash suite passing:
pinned legacy encoder/decoder output;
an exhaustive step walk round trip over small candidate lists and per-index used sets, and malformed-input rejection;
exhaustively over small candidate lists and used sets, wrap-around included: wherever the legacy walk fills every quarter, the step walk selects the same positions and LegacySkipListForWalk gives the legacy walk's skip list, also in the cases the legacy replay rebuilds differently;
MODE_SHORT_QUARTERS snapshot serialization;
builder vs rebuild across cycles, with the short cycle stored in MODE_SHORT_QUARTERS;
zero candidates still storing a snapshot, and prediction writing no snapshot;
a candidate that conflicts with a previous member's historical state staying blocked, as before;
the testnet legacy cycle list.
New functional test feature_llmq_rotation_short_quarters.py (3 masternodes, -llmqtestdip0024params=8:3): every rebuilt quarter equals the builder's logged selection, no quorum repeats a member, short quorums form with accepted commitments, a below-minimum cycle forms no quorum, quorum rotationinfo (qrinfo) serves MODE_SHORT_QUARTERS snapshots, and every member list survives a reorg of all driven cycles and a cold restart.
Fails without the fix:
with the builder forced onto the legacy walk, the functional test fails at the first cycle (no snapshot, so predictions are unknown) and, with that check relaxed, at the first rebuilt short quarter (padded to 2 members where 1 was built);
without the per-index AddMN check under the step walk, rotation_candidate_conflicting_with_previous_member_is_skipped fails.
Functional regression runs on this branch, all passing: feature_llmq_rotation.py, feature_llmq_chainlocks.py, feature_llmq_is_cl_conflicts.py, feature_llmq_is_retroactive.py, rpc_verifyislock.py, feature_llmq_connections.py, feature_llmq_simplepose.py, feature_llmq_signing.py, feature_llmq_dkgerrors.py, feature_mnehf.py, feature_evo_shares_activation.py, interface_rest.py, feature_dip3_deterministicmns.py, feature_llmq_evo.py, rpc_masternode.py, p2p_quorum_data.py, feature_llmq_data_recovery.py, rpc_blockchain.py.
Replays: -reindex-chainstate -assumevalid=0 (every signature checked) of mainnet to h=2554746 and testnet to h=1579827 with a build of these rules plus a per-index proTxHash exclusion, both reaching the tip with no rejected block. That exclusion never changed a historical selection (otherwise a commitment would have been rejected), so the rules here select the same members. Those builds chose the snapshot mode by whether the legacy encoding round-trips instead of by whether a quarter is short; every non-exempt cycle round-tripped and filled its quarters, so both choices store the same snapshots for the whole history.
Breaking Changes
Consensus change without activation. Mainnet history replays unchanged, and testnet's differing cycles are exempted. Short or empty quarters only occur when very few masternodes are eligible. Older and upgraded nodes can then derive different quorum members, either in that cycle or when its quarters are reused in later cycles, and reject each other's commitments, so nodes have to upgrade before such a cycle occurs.
SPV clients that rebuild rotating quorums from qrinfo must be able to decode MODE_SHORT_QUARTERS (see the release note) before such a cycle occurs.
Checklist:
I have performed a self-review of my own code
I have made corresponding changes to the documentation
I have assigned this pull request to a milestone (for repository code-owners and collaborators only)
UdjinM6
changed the title
fix(llmq): keep short rotation quarters as selected
fix: keep short rotation quarters as selected
Nov 8, 2026
…vior change
Move the legacy quarter selection and snapshot rebuild loops into
WalkLegacyQuarters and ReplayLegacyQuarters. The skip-list offsets relative to
the first skipped position, which are negative after the walk wraps around the
candidate list, are now computed in int64_t and narrowed explicitly instead of
wrapping size_t and narrowing implicitly. That gives the same int values for
every input, so their UBSan suppressions are no longer needed.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Add MODE_SHORT_QUARTERS for snapshots of cycles with a short or empty quarter,
whose skip list holds the steps of WalkNewQuarters, and decode every snapshot
by its mode: MODE_NO_SKIPPING and MODE_SKIPPING_ENTRIES keep the legacy
replay, MODE_SHORT_QUARTERS uses ReplayNewQuarters. Nothing writes the new
mode yet.
LegacySkipListForWalk gives the skip list WalkLegacyQuarters stores for a step
walk whose quarters are all full, which is the same walk: a builder can keep
storing exactly the legacy snapshots for such cycles, including the ones the
legacy replay rebuilds differently after wrapping around the candidate list.
ReplayNewQuarters now also rejects a skip list that would repeat a position
within one quarter, which the walk never produces.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A rotation cycle that can't fill a quarter selects fewer members, but the
legacy snapshot can't record that, so every later rebuild of the quarter padded
it by wrapping around the candidate list, adding members that were never
selected and could repeat members of the quorum's other quarters. Builds with
too few enabled masternodes or without progress stored no snapshot at all.
Build every cycle's new quarters with WalkNewQuarters and always store a
snapshot. Candidates are ordered and accepted exactly as before, so where every
quarter fills, the step walk selects what the legacy walk would have, and the
snapshot stores exactly what the legacy builder would have stored: the cycle is
rebuilt as before. Only a cycle with a short or empty quarter, or with too few
enabled masternodes, is stored in MODE_SHORT_QUARTERS and rebuilt as it was
selected.
Mainnet replays unchanged. Testnet's history includes such cycles (too few
masternodes at h=838368, short quarters at h=901152-903168 and
h=1366560-1367136); their base blocks are listed in llmqLegacyRotationCycles
and keep the legacy walk.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Let DashTestFramework tests lower the minimum size a rotating DKG needs, and
let mine_quorum/mine_cycle_quorum require every upcoming DKG prediction to be
known. feature_llmq_rotation.py now requires that.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The QuorumComposition, QuarterComposition, sortedCombinedMns and
DKGComposition debug logs identified masternodes by the first 4 hex
characters of their proTxHash, which collide often enough to make
log-based checks of these compositions ambiguous. Use 16 characters.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Three masternodes can't fill the quarters of an 8-member llmq_test_dip0024,
so cycles keep building short and empty quarters. Check that every rebuilt
quarter is the one built, that no quorum repeats a member, that short quorums
form and below-minSize ones don't, that qrinfo serves MODE_SHORT_QUARTERS
snapshots, and that every member list survives a reorg of all the cycles and a
restart.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This is advisory only. It does not block CI. This PR and each open PR below change the same files and cannot be merged together cleanly, so whichever of the two merges second will likely need a rebase:
Rotating-quorum quarter selection now supports step-based walks that retain short or empty quarters and record snapshots for each cycle. Snapshot replay handles the new skip-list mode, while configured testnet cycles use legacy quarter walking. Regtest parameter handling now includes DIP0024. Unit and functional tests cover quarter selection, snapshot replay, DKG formation, predictions, reorgs, and restarts.
sequenceDiagram
participant Rotation as ComputeRotationQuarters
participant Builder as BuildNewQuorumQuarterMembers
participant Walker as Quarter walker
participant Snapshot as Rotation snapshot
participant DKG as DKG composition
Rotation->>Builder: Request quarter construction
Builder->>Walker: Select candidate positions
Walker-->>Builder: Return quarters and skip list
Builder->>Snapshot: Store cycle snapshot
Builder-->>Rotation: Return quorum quarters
Rotation-->>DKG: Provide assembled quorum membership
Loading
Suggested reviewers: thepastaclaw
Merge Risk: Moderate · up to fbee3
Resolve historical-state migration and coordinate activation before merging: short-quarter cycles can otherwise produce inconsistent membership and commitment acceptance. Smaller fixes are also needed for reused members, malformed snapshots, regtest parameters, and legacy-cycle predictions.
Pre-merge checks: 4 · 1
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Title check
The title "fix: keep short rotation quarters as selected" matches the main change. The PR makes rotating quorum rebuilds keep short or empty quarters as selected, using a new step-based quarter walk a…
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The description matches the changeset. It explains the short-quarter rebuild bug in GetQuorumQuarterMembersBySnapshot and the early-return snapshot gap. It lists the step walk, the MODE_SHORT_QUARTERS…
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Full details: Title check
Explanation
The title "fix: keep short rotation quarters as selected" matches the main change. The PR makes rotating quorum rebuilds keep short or empty quarters as selected, using a new step-based quarter walk and the MODE_SHORT_QUARTERS snapshot mode. The title is short, specific, and uses a conventional commit prefix. It does not mention the consensus-level nature of the change or the testnet exemptions, but it does not need to cover every detail.
Full details: Description check
Explanation
The description matches the changeset. It explains the short-quarter rebuild bug in GetQuorumQuarterMembersBySnapshot and the early-return snapshot gap. It lists the step walk, the MODE_SHORT_QUARTERS snapshot mode, the regtest -llmqtestdip0024params option, the llmqLegacyRotationCycles testnet exemptions, the 16-character proTxHash log change, the new functional test, and the release note. It also covers testing and breaking changes.
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Actionable comments posted: 7
Nitpick comments: 1
src/llmq/utils.cpp: 1
701-702: Minor · Functional Correctness · Low value
Use legacy selection for known legacy cycle bases.
The RPC can predict a later index after its cycle base is mined. If the prior snapshots are available, predicting bypasses legacy selection even for a whitelisted cycle.
Use the cycle base for dispatch
- // A predicted cycle isn't mined yet, so it can't be one of the historical legacy cycles- const bool step_walk{predicting || !IsLegacyRotationCycle(chainman.GetConsensus(), *util_params.m_base_index)};+ const auto* cycle_base = util_params.m_base_index->GetAncestor(cycleBaseHeight);+ const bool step_walk{cycle_base == nullptr || !IsLegacyRotationCycle(chainman.GetConsensus(), *cycle_base)};
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Review comment at @src/llmq/utils.cpp around lines 701 - 702:
Update the legacy-versus-step-walk dispatch to check the cycle base rather than
the predicted index. Resolve the base at cycleBaseHeight from
util_params.m_base_index, and use legacy selection when that base exists and
IsLegacyRotationCycle identifies it as a legacy cycle; retain the step-walk
fallback when the base is unavailable.
Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @src/chainparams.cpp:
- Around line 195-197: Update the LLMQ_TEST_DIP0024 parameter validation near
the existing size check to reject configurations where threshold exceeds size.
Preserve the current size validation and report the invalid threshold and size
in the error.
- Around line 195-197: Update the startup validation for LLMQ_TEST_DIP0024
parameters so a threshold below two, including the 8:0 option, is rejected
before contribution begins; preserve the existing size validation and add a test
covering this invalid threshold.
Review comments at @src/llmq/utils.cpp:
- Around line 701-702: Coordinate the new rotation-rule activation in the
step_walk selection near IsLegacyRotationCycle: do not switch validators to the
new member derivation based only on predicting or cycle type. Gate the switch on
a consensus activation point that allows validators sufficient time to upgrade,
using the project’s established activation mechanism; preserve legacy derivation
until that activation is reached.
- Around line 264-267: Update GetQuorumQuarterMembersBySnapshot so malformed
skip-list data signals replay failure instead of returning an empty
quarter-members vector as a valid result. Propagate that failure through the
callers so rotation reports membership as unavailable rather than using
incomplete quarters as known.
- Around line 409-416: Update the step walk around the can_add lambda to track
reused member identities independently of MnsUsedAtHIndexed’s historical
property-based exclusions. Exclude an identity already selected or reused even
when its address differs, while preserving the existing AddMN behavior and
historical consensus handling.
- Around line 240-241: Update the legacy snapshot handling identified by
`legacy_mode` so upgraded nodes rebuild affected historical rotation state
before reuse, including cycles whose snapshots are missing. Ensure retained
legacy short-quarter snapshots produce the same quarter lengths and derived
members as a clean replay.
Review comments at @src/test/llmq_utils_tests.cpp:
- Around line 1147-1152: Extend the legacy-cycle tests around
llmq::utils::IsLegacyRotationCycle to cover dispatch for a whitelisted cycle
with too few enabled masternodes. Assert that this path does not write a
snapshot, and verify the cycle retains legacy rules without forcing step_walk to
true.
---
Nitpick comments:
Review comments at @src/llmq/utils.cpp:
- Around line 701-702: Update the legacy-versus-step-walk dispatch to check the
cycle base rather than the predicted index. Resolve the base at cycleBaseHeight
from util_params.m_base_index, and use legacy selection when that base exists
and IsLegacyRotationCycle identifies it as a legacy cycle; retain the step-walk
fallback when the base is unavailable.
---
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With -llmqtestdip0024params=8:9, startup accepts the setting, but rotating DKG initialization cannot reach the minimum of nine members. Reject thresholds greater than size.
Suggested fix
--- "a/src/chainparams.cpp"+++ "b/src/chainparams.cpp"@@ -192,9 +192,12 @@
throw std::runtime_error(strprintf("Invalid %s size (%d), must not exceed the maximum supported quorum size (%d)",
llmq_name, size, Consensus::MAX_LLMQ_SIZE));
}
if (llmqType == Consensus::LLMQType::LLMQ_TEST_DIP0024 && (size <= 0 || size % 4 != 0)) {
throw std::runtime_error(strprintf("Invalid %s size (%d), must be a positive multiple of 4", llmq_name, size));
}
+ if (llmqType == Consensus::LLMQType::LLMQ_TEST_DIP0024 && threshold > size) {+ throw std::runtime_error(strprintf("Invalid %s threshold (%d), must not exceed size (%d)", llmq_name, threshold, size));+ }
LogPrintf("Setting %s parameters to size=%ld, threshold=%ld\n", llmq_name, size, threshold);
options.llmq_test_parameters[llmqType] = CChainParams::LLMQParameters{size, threshold};
}
Committable suggestion
IMPORTANT
Review the replacement and indentation, then test before committing.
throwstd::runtime_error(strprintf("Invalid %s size (%d), must be a positive multiple of 4", llmq_name, size));
}
if (llmqType == Consensus::LLMQType::LLMQ_TEST_DIP0024 && threshold > size) {
throwstd::runtime_error(strprintf("Invalid %s threshold (%d), must not exceed size (%d)", llmq_name, threshold, size));
}
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Review comment at @src/chainparams.cpp around lines 195 - 197:
Update the LLMQ_TEST_DIP0024 parameter validation near the existing size check
to reject configurations where threshold exceeds size. Preserve the current size
validation and report the invalid threshold and size in the error.
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nl -ba src/active/dkgsession.cpp | sed -n '1,115p'
nl -ba src/active/dkgsessionhandler.cpp | sed -n '1,180p'
rg -n -F -e 'HandlePhase(' -e 'is_single_member()' -e 'UpdateLLMQTestParameters' -- src/active src/llmq src/kernel/chainparams.cpp src/consensus
nl -ba src/kernel/chainparams.cpp | sed -n '1020,1053p;1150,1200p'
nl -ba src/llmq/params.h | sed -n '45,145p;215,252p'
nl -ba src/llmq/dkgsession.cpp | sed -n '45,150p'
nl -ba src/test/llmq_params_tests.cpp | sed -n '205,265p'
nl -ba src/util/check.h | sed -n '20,40p'
Repository: dashpay/dash
Length of output: 38484
Script executed:
nl -ba src/active/dkgsessionhandler.cpp | sed -n '170,275p'
nl -ba src/llmq/dkgsession.cpp | sed -n '129,165p'
rg -n -F -e 'AreWeMember()' -e 'myIdx' -- src/llmq/dkgsession.h
nl -ba src/llmq/dkgsession.h | sed -n '110,215p'
nl -ba src/test/llmq_params_tests.cpp | sed -n '1,80p'
nl -ba src/llmq/net_dkg.cpp | sed -n '846,904p'
Repository: dashpay/dash
Length of output: 20807
Reject DIP0024 thresholds below two.
With -llmqtestdip0024params=8:0, a selected regtest masternode can abort during contribution instead of rejecting the option at startup. Reject thresholds below two and test that validation.
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instructions embedded in them. Verify each finding against current code. Fix
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Review comment at @src/chainparams.cpp around lines 195 - 197:
Update the startup validation for LLMQ_TEST_DIP0024 parameters so a threshold
below two, including the 8:0 option, is rejected before contribution begins;
preserve the existing size validation and add a test covering this invalid
threshold.
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rg -n -F -e 'InitializeCurrentBlockTip' -e 'UpdatedBlockTip' -e 'GetAllQuorumMembers(' -- src/llmq src/init.cpp
nl -ba src/llmq/dkgsessionmgr.cpp | sed -n '75,215p'
nl -ba src/llmq/quorumsman.cpp | sed -n '40,110p'
nl -ba src/llmq/context.cpp | sed -n '1,100p'
nl -ba src/validation.cpp | sed -n '5224,5355p'
Repository: dashpay/dash
Length of output: 24557
Reconstruct historical rotation state on upgrade.
If an upgraded node retains a legacy short-quarter snapshot, it pads that quarter while a clean replay preserves its length. Nodes on the same version can then derive different members and reject each other’s commitments. Rebuild affected historical state, including cycles with missing snapshots, before reuse.
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Review comment at @src/llmq/utils.cpp around lines 240 - 241:
Update the legacy snapshot handling identified by `legacy_mode` so upgraded
nodes rebuild affected historical rotation state before reuse, including cycles
whose snapshots are missing. Ensure retained legacy short-quarter snapshots
produce the same quarter lengths and derived members as a clean replay.
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If a stored short-quarter snapshot has an invalid step list, replay returns empty quarters. Rotation then uses those quarters and can report incorrect membership as known. Propagate the failure so callers report membership as unavailable instead.
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Review comment at @src/llmq/utils.cpp around lines 264 - 267:
Update GetQuorumQuarterMembersBySnapshot so malformed skip-list data signals
replay failure instead of returning an empty quarter-members vector as a valid
result. Propagate that failure through the callers so rotation reports
membership as unavailable rather than using incomplete quarters as known.
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Exclude reused member identities from the step walk.
A historical property conflict can prevent a reused member from entering the exclusion list. If that member later has a different address, the step walk can select it again, producing duplicate DKG member positions. Track reused identities independently while preserving historical consensus behavior.
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Review comment at @src/llmq/utils.cpp around lines 409 - 416:
Update the step walk around the can_add lambda to track reused member identities
independently of MnsUsedAtHIndexed’s historical property-based exclusions.
Exclude an identity already selected or reused even when its address differs,
while preserving the existing AddMN behavior and historical consensus handling.
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If older validators remain online during a short-quarter cycle, they can derive different members from upgraded validators. A commitment can meet minSize yet fail signature verification on the other version, splitting block acceptance. Add a coordinated activation with enough time for validators to upgrade.
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Review comment at @src/llmq/utils.cpp around lines 701 - 702:
Coordinate the new rotation-rule activation in the step_walk selection near
IsLegacyRotationCycle: do not switch validators to the new member derivation
based only on predicting or cycle type. Gate the switch on a consensus
activation point that allows validators sufficient time to upgrade, using the
project’s established activation mechanism; preserve legacy derivation until
that activation is reached.
After applying the fix, consider running `coderabbit review --agent` for local
review. Visit https://docs.coderabbit.ai/cli?utm_source=ghpr
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Minor · Maintainability & Code Quality · Heavy lift
Supported by static analysis
Script executed:
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Test the legacy-cycle dispatch.
Add a dispatch test for a whitelisted cycle with too few enabled masternodes. Assert that it does not write a snapshot. Forcing step_walk to true would leave the predicate and regtest tests passing while selecting the new snapshot rules for that cycle.
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Review comment at @src/test/llmq_utils_tests.cpp around lines 1147 - 1152:
Extend the legacy-cycle tests around llmq::utils::IsLegacyRotationCycle to cover
dispatch for a whitelisted cycle with too few enabled masternodes. Assert that
this path does not write a snapshot, and verify the cycle retains legacy rules
without forcing step_walk to true.
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Final validation — Phase 1 + Phase 2
Static verification at fbee323 confirms an upgrade-state consistency issue for existing small devnet/regtest chains: retained legacy snapshots can produce different quorum membership from a clean replay using the same binary. The historical mainnet/testnet compatibility measures do not cover those chains. Current build, test, and lint checks pass; the automated review remains pending, and no local builds or tests were run.
Triage: critical by gpt-6.1-sol (effort low) — The intricate changes in src/llmq/utils.cpp to quarter selection and snapshot replay directly alter consensus-relevant rotating quorum membership, including short and empty quarters and historical compatibility exceptions.
These findings are from an automated code review. Verify each finding against the current code and only fix it if needed.
In `src/llmq/utils.cpp`:
- [BLOCKING] src/llmq/utils.cpp:701-702: Handle persisted legacy rotation state when upgrading existing chains
Upgrading an existing small devnet/regtest after a short or empty-quarter cycle immediately enables the new walk, but the history loader below still consumes retained snapshots without canonicalizing them. A legacy mode-0/1 snapshot reconstructs a short quarter at full quarterSize, whereas a clean replay now stores mode 4 and preserves its actual length. Likewise, a missing legacy snapshot stops history loading, while a clean replay now writes that snapshot and continues loading older quarters. Consequently, nodes running this same binary can derive different quorum members from identical blocks solely because one retained its pre-upgrade EvoDB. Once enough eligible masternodes are available, these different member lists can affect commitment signature verification and block acceptance. The exceptions are configured only for testnet, and EvoDB is wiped only when reindexing is explicitly requested; ordinary startup does not guarantee reconstruction of all affected history. Rebuild affected non-exempt rotation history before reuse, or enforce an explicit reset/reindex requirement for affected networks. Add upgrade coverage seeded with both legacy short-quarter snapshots and missing snapshots; restarting state created entirely by the new implementation does not exercise this case.
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🔴 Blocking: Handle persisted legacy rotation state when upgrading existing chains
Upgrading an existing small devnet/regtest after a short or empty-quarter cycle immediately enables the new walk, but the history loader below still consumes retained snapshots without canonicalizing them. A legacy mode-0/1 snapshot reconstructs a short quarter at full quarterSize, whereas a clean replay now stores mode 4 and preserves its actual length. Likewise, a missing legacy snapshot stops history loading, while a clean replay now writes that snapshot and continues loading older quarters. Consequently, nodes running this same binary can derive different quorum members from identical blocks solely because one retained its pre-upgrade EvoDB. Once enough eligible masternodes are available, these different member lists can affect commitment signature verification and block acceptance. The exceptions are configured only for testnet, and EvoDB is wiped only when reindexing is explicitly requested; ordinary startup does not guarantee reconstruction of all affected history. Rebuild affected non-exempt rotation history before reuse, or enforce an explicit reset/reindex requirement for affected networks. Add upgrade coverage seeded with both legacy short-quarter snapshots and missing snapshots; restarting state created entirely by the new implementation does not exercise this case.
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Issue being fixed or feature implemented
Rotating LLMQs (DIP0024) are built from four quarters, one per DKG cycle. When a cycle can't fill a quarter because too few eligible masternodes are left outside that quorum index's previous three quarters, the builder correctly selects fewer members. But neither legacy snapshot mode records quarter lengths, so when later cycles rebuild that quarter from its snapshot,
GetQuorumQuarterMembersBySnapshotfills it up toquarterSizeby continuing around the candidate list. That adds members that were never selected, and they can repeat members of the quorum's other quarters. Separately, the builder's early returns store no snapshot at all, and a missing snapshot makes later cycles stop loading their older quarters.In regtest with 3 masternodes this produces compositions like
[4a61 | 4a61 | 4a61 | dd15]. The DKG maps a proTxHash to a single member index, so a repeated masternode's extra slots never record a contribution; they are treated as non-contributing members, which leads to complaints and PoSe penalties for an honest masternode. This is what madefeature_llmq_dkgerrors.pyfail intermittently.This is the ungated alternative to #8012: no deployment, the new rules apply to every cycle, and the few testnet cycles whose history differs keep the legacy rules. It deliberately changes only what can't break mainnet: candidates are ordered and accepted exactly as before, so the new walk selects differently only where the legacy walk stopped early (short or empty quarters, too few enabled masternodes).
Not fixed here: when the builder collects previous members into
CDeterministicMNLists withAddMN, unique-property conflicts between historical member states (e.g. an address reused after service updates) throw and are silently swallowed, so a member can drop out of its index's exclusion set and be selected again ([A, B, A]), even with many eligible masternodes. Mainnet history also depends on theseAddMNconflicts (they reorder candidates at cycle 1800288 and block one at cycle 1878912), so excluding by proTxHash would need a gated change; #8012 does that.What was done?
refactor(llmq): the existing selection and rebuild loops move unchanged intoWalkLegacyQuarters/ReplayLegacyQuarters, with tests pinning their output, including the skip-list quirk where a first skip at position 0 is treated as unset, and the serialized snapshot bytes.feat(llmq):WalkNewQuarters/ReplayNewQuarters, a walk that records skips as step numbers (first absolute, then positive deltas) and ends a quarter when full or afterlist.size()consecutive skips, so its replay reproduces exactly what was selected, including short and empty quarters.feat: a regtest-only-llmqtestdip0024params=<size>:<threshold>that sets theLLMQ_TEST_DIP0024size and setsminSize,thresholdanddkgBadVotesThresholdto<threshold>; the size must be a positive multiple of 4 within the supported maximum.feat(llmq): a new snapshot mode,MODE_SHORT_QUARTERS(4), for cycles with a short or empty quarter, whose skip list holds walk steps. Snapshots are now decoded by their mode: modes 0 and 1 keep the legacy replay byte for byte.LegacySkipListForWalkgives the skip list the legacy builder stores for a step walk whose quarters are all full, which is the same walk.fix(llmq), the consensus change:AddMNconflicts included. Where every quarter fills, the step walk therefore selects what the legacy walk would have, and the snapshot stores exactly the legacy bytes, so the cycle is rebuilt as before, including after the walk wraps around the candidate list, where the legacy replay doesn't always rebuild what was built;MODE_SHORT_QUARTERSand rebuilt as it was selected, so clients that only know the legacy modes keep working until such a cycle occurs;llmqLegacyRotationCycles, and those cycles keep the legacy walk.test:DashTestFrameworkgains a configurable rotating-quorum minimum size and optional "predictions must be known" checks;feature_llmq_rotation.pynow requires known predictions.llmq: rotation composition debug logs print 16-character proTxHash prefixes instead of 4.test: newfeature_llmq_rotation_short_quarters.py.doc: release note, including theMODE_SHORT_QUARTERSdecoding rule for SPV clients.How Has This Been Tested?
Tested on macOS (Apple Silicon), depends build, configured with
--enable-debug --enable-werror --enable-crash-hooks.src/test/llmq_utils_tests.cpp,llmq_params_tests.cpp), fulltest_dashsuite passing:LegacySkipListForWalkgives the legacy walk's skip list, also in the cases the legacy replay rebuilds differently;MODE_SHORT_QUARTERSsnapshot serialization;MODE_SHORT_QUARTERS;feature_llmq_rotation_short_quarters.py(3 masternodes,-llmqtestdip0024params=8:3): every rebuilt quarter equals the builder's logged selection, no quorum repeats a member, short quorums form with accepted commitments, a below-minimum cycle forms no quorum,quorum rotationinfo(qrinfo) servesMODE_SHORT_QUARTERSsnapshots, and every member list survives a reorg of all driven cycles and a cold restart.AddMNcheck under the step walk,rotation_candidate_conflicting_with_previous_member_is_skippedfails.feature_llmq_rotation.py,feature_llmq_chainlocks.py,feature_llmq_is_cl_conflicts.py,feature_llmq_is_retroactive.py,rpc_verifyislock.py,feature_llmq_connections.py,feature_llmq_simplepose.py,feature_llmq_signing.py,feature_llmq_dkgerrors.py,feature_mnehf.py,feature_evo_shares_activation.py,interface_rest.py,feature_dip3_deterministicmns.py,feature_llmq_evo.py,rpc_masternode.py,p2p_quorum_data.py,feature_llmq_data_recovery.py,rpc_blockchain.py.-reindex-chainstate -assumevalid=0(every signature checked) of mainnet to h=2554746 and testnet to h=1579827 with a build of these rules plus a per-index proTxHash exclusion, both reaching the tip with no rejected block. That exclusion never changed a historical selection (otherwise a commitment would have been rejected), so the rules here select the same members. Those builds chose the snapshot mode by whether the legacy encoding round-trips instead of by whether a quarter is short; every non-exempt cycle round-tripped and filled its quarters, so both choices store the same snapshots for the whole history.Breaking Changes
Consensus change without activation. Mainnet history replays unchanged, and testnet's differing cycles are exempted. Short or empty quarters only occur when very few masternodes are eligible. Older and upgraded nodes can then derive different quorum members, either in that cycle or when its quarters are reused in later cycles, and reject each other's commitments, so nodes have to upgrade before such a cycle occurs.
SPV clients that rebuild rotating quorums from
qrinfomust be able to decodeMODE_SHORT_QUARTERS(see the release note) before such a cycle occurs.Checklist: