[Bug] CheckpointFile cannot persist empty checkpoints

[yuluo-yx]

Runtime platform environment

macOS; reproduced with a temporary checkpoint file in the common module.

RocketMQ version

Branch: develop
Git commit: fd0c95920e0deac96ce2ae27442747cc5e65e930

JDK Version

Eclipse Temurin 17.0.19+10

Describe the Bug

CheckpointFile.write returns immediately for an empty entry list, leaving old entries on disk. In addition, read() treats a valid empty primary file as a reason to load the backup, so stale backup entries can be restored instead of an intentionally empty state.

Steps to Reproduce

1. Write a checkpoint containing entries.
2. Write an empty entry list to the same CheckpointFile.
3. Read the checkpoint.
4. Observe that old entries remain. A valid empty primary file also causes read() to return entries from its older backup.

What Did You Expect to See?

An empty list should be persisted as a valid zero-entry checkpoint, and reading that valid primary should return an empty list. Backup fallback should only occur when the primary is missing or invalid.

What Did You See Instead?

Empty writes are ignored, and a valid empty primary can be replaced in memory by stale backup content.

Additional Context

The existing count and CRC format can represent an empty checkpoint without a format change.

[RockteMQ-AI]

Issue Evaluation

Category: bug | Status: Confirmed

The reported issue has been verified against the current codebase (commit fd0c959).

Root Cause: CheckpointFile.write() returns immediately when the entry list is empty (line 74: if (entries.isEmpty()) { return; }), never persisting the empty state. Additionally, read() falls back to the backup file when the primary returns an empty list (CollectionUtils.isEmpty(result)), so a valid empty primary can be replaced by stale backup data.

Impact: Components relying on checkpoint persistence (e.g., consumer offset tracking) may recover stale state after a restart if the last checkpoint was intended to be empty.

Severity: medium — data correctness issue in edge case (empty checkpoint scenarios)

Suggested Fix:

• write(): Persist empty checkpoints by writing 0\n<crc32>\n to both primary and backup files.
• read(): Only fall back to backup when the primary file is missing or unreadable, not when it contains a valid empty checkpoint.

An automated fix proposal will be generated. Reply /approve to proceed with PR generation.

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Automated evaluation by RockteMQ-AI