Decouple CoordinatorCommitHandler from TransactionContext and WriteSetEncoder

[brfrn169]

Description

CoordinatorCommitHandler writes only the Coordinator state table, yet it took a full TransactionContext and encoded the write set itself via WriteSetEncoder, tying it to the snapshot-bearing execution context. This PR decouples the handler so it operates on a transaction ID plus a pre-encoded WriteSet, moving write-set encoding ownership up to the orchestrator (CommitHandler). This sharpens the layering — the Coordinator-side state logic now depends only on what it actually writes — and lets those state writes be driven by ID.

Related issues and/or PRs

• Split CommitHandler into an orchestrator and specialized handlers #3653

Changes made

• CoordinatorCommitHandler: commitState / abortState / handleCommitConflict now take a transaction ID and a pre-encoded WriteSet (commitState also takes the committedAt to stamp). The handler no longer references TransactionContext or WriteSetEncoder.
• CommitHandler (orchestrator): now owns the WriteSetEncoder, encodes the write set, and supplies committedAt before delegating. commitState / abortState are encoding delegators (not thin pass-throughs), which is documented on the class.
• Group commit: the Emittable value is now a (fullId, WriteSet) carrier (new CoordinatorGroupCommitValue), so the Emitter is encoder-free — it derives each child ID from the carried full ID and stamps the pre-encoded write set. The group-commit entry point is named groupCommitState (distinct from the base commitState, whose signature differs) to prevent a caller from silently binding to the base direct-putState overload, and slot cancellation is ID-based (cancelGroupCommit).
• Removed WriteSetEncoder#encodeMultiGroupWriteSet and its CoordinatorGroupCommitKeyManipulator dependency (now unused).
• Reworked the unit tests to the ID-based signatures; commitState delegation is routed through protected hooks so the group-commit subclass asserts the 2-arg groupCommitState while the base asserts the 3-arg orchestrator-provided variant.

Checklist

• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation to reflect the changes.
• I have considered whether similar issues could occur in other products, components, or modules if this PR is for bug fixes.
• Any remaining open issues linked to this PR are documented and up-to-date (Jira, GitHub, etc.).
• Tests (unit, integration, etc.) have been added for the changes.
• My changes generate no new warnings.
• Any dependent changes in other PRs have been merged and published.

Additional notes (optional)

N/A

Release notes

N/A

[gemini-code-assist]

Code Review

This pull request refactors the Consensus Commit transaction commit handler to decouple CoordinatorCommitHandler from WriteSetEncoder. The orchestrators (CommitHandler and CommitHandlerWithGroupCommit) now handle write set encoding before delegating to the coordinator handlers, and the group commit emitter merges pre-encoded write sets using a new CoordinatorGroupCommitValue carrier. Feedback on the changes highlights a potential issue where commitStateWithoutWriteSet and abortStateWithoutWriteSet are not overridden in CommitHandlerWithGroupCommit, which could bypass the group committer and lead to slot leaks.

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[Copilot]

Pull request overview

Refactors Consensus Commit coordinator-state writing to be driven by transaction ID plus a pre-encoded WriteSet, decoupling CoordinatorCommitHandler (and the group-commit emitter) from snapshot-bearing TransactionContext and from WriteSetEncoder. This supports upcoming TwoPhaseCommit flows that need to write coordinator state by ID without holding a transaction snapshot.

Changes:

• CoordinatorCommitHandler APIs now accept (txId, WriteSet?, committedAt) for commit and (txId, WriteSet?) for abort; conflict handling is ID-based.
• Orchestrator (CommitHandler / CommitHandlerWithGroupCommit) now owns WriteSetEncoder and supplies encoded write sets (and non-group committedAt) when delegating.
• Group commit now buffers a (fullId, WriteSet?) carrier (CoordinatorGroupCommitValue), and the emitter merges/stamps per-child entry groups at emit time; tests updated accordingly.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
core/src/main/java/com/scalar/db/transaction/consensuscommit/CommitHandler.java	Moves write-set encoding (and non-group committedAt) responsibility into the orchestrator before delegating to coordinator handler.
core/src/main/java/com/scalar/db/transaction/consensuscommit/CommitHandlerWithGroupCommit.java	Routes coordinator commit-state writes through group commit using encoded write sets; makes slot cancellation ID-based.
core/src/main/java/com/scalar/db/transaction/consensuscommit/CoordinatorCommitHandler.java	Converts coordinator-side state writes/conflict handling to operate on txId + pre-encoded WriteSet.
core/src/main/java/com/scalar/db/transaction/consensuscommit/CoordinatorCommitHandlerWithGroupCommit.java	Updates group-commit path to buffer (fullId, WriteSet) values and merge/stamp at emit time; renames APIs to avoid accidental binding.
core/src/main/java/com/scalar/db/transaction/consensuscommit/CoordinatorGroupCommitter.java	Updates the group committer value type to CoordinatorGroupCommitValue.
core/src/main/java/com/scalar/db/transaction/consensuscommit/CoordinatorGroupCommitValue.java	Introduces a carrier for group-commit buffering: full transaction ID + pre-encoded WriteSet.
core/src/main/java/com/scalar/db/transaction/consensuscommit/WriteSetEncoder.java	Removes now-unused multi-group encoding logic and its key-manipulator dependency.
core/src/test/java/com/scalar/db/transaction/consensuscommit/CommitHandlerTest.java	Updates orchestration tests to reflect ID-based coordinator handler APIs and verify orchestrator encoding delegation.
core/src/test/java/com/scalar/db/transaction/consensuscommit/CommitHandlerWithGroupCommitTest.java	Adjusts group-commit orchestration assertions to target groupCommitState and ID-based cancellation.
core/src/test/java/com/scalar/db/transaction/consensuscommit/CoordinatorCommitHandlerTest.java	Reworks direct coordinator-handler tests to pass IDs and pre-encoded write sets.
core/src/test/java/com/scalar/db/transaction/consensuscommit/CoordinatorCommitHandlerWithGroupCommitTest.java	Reworks group-commit handler/emitter tests to use pre-encoded write sets and value carriers.
core/src/test/java/com/scalar/db/transaction/consensuscommit/CoordinatorGroupCommitterTest.java	Updates group-committer tests to buffer CoordinatorGroupCommitValue instead of TransactionContext.

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[Copilot]

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

[komamitsu]

LGTM! 👍

[feeblefakie]

LGTM! Thank you!