[Improvement] Deprecate legacy Broker DLedger mode

[RongtongJin]

Motivation

RocketMQ still exposes the legacy Broker DLedger mode through enableDLegerCommitLog=true, DLedgerCommitLog, and the related MessageStoreConfig accessors. For new deployments, Controller mode is the recommended automatic failover path.

This proposal is limited to Broker DLedger mode. It does not deprecate the DLedger-backed Controller implementation.

Proposed changes

• Mark DLedgerCommitLog and the Broker-DLedger-specific MessageStoreConfig accessors as deprecated.
• Log a clear warning when a Broker starts with enableDLegerCommitLog=true.
• Keep existing Broker DLedger behavior, dependencies, and tests intact for compatibility.
• Do not remove or disable the feature because existing deployments may still rely on it.

Compatibility

Existing clusters continue to start and operate unchanged. The only runtime difference is a deprecation warning for Brokers that explicitly enable the legacy mode.

[RockteMQ-AI]

Issue Evaluation

Category: type/enhancement | Status: Evaluated

Feasibility: Feasible
Scope: DLedgerCommitLog, MessageStoreConfig (Broker DLedger-specific accessors)
Compatibility: No breaking changes — existing clusters continue to operate unchanged

This is a well-scoped deprecation. The distinction between Broker DLedger mode (deprecated) and DLedger-backed Controller (retained) is clearly documented. The approach — add @Deprecated annotations + startup warning log while keeping full backward compatibility — is the correct way to signal deprecation without disrupting existing deployments.

Assessment:

• Clear motivation: Controller mode is the recommended path for new deployments
• Compatibility is properly considered (no removal, just deprecation markers)
• Scope is correctly limited to Broker DLedger mode only

This looks ready for implementation.

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Automated evaluation by RockteMQ-AI