Introducing ImportWAL for IoTDB WAL Recovery

[Tian Jiang <jt...@163.com>]

Greetings,

  I’d like to introduce ImportWAL, a command-line utility for recovering data from WAL files into an existing IoTDB instance.
When a DataNode fails or its WAL directory must be moved aside—for example, because of WAL corruption or insufficient disk space—the WAL may still contain unflushed writes, deletes, and MemTable snapshots. ImportWAL makes it possible to extract and replay this recoverable data without restoring the entire original DataNode. 
The tool is designed for operational recovery scenarios and supports both IoTDB data models. It can process an individual WAL file or a WAL directory, replay data into a prepared target schema, and provide progress and recovery statistics. Operators can also review potentially destructive or unsupported entries during replay and keep the original WAL files available for verification and archival. 
  A typical recovery workflow is:
  1. Stop the affected DataNode and preserve the original WAL files.
  2. Prepare the target IoTDB schema or table structure.
  3. Replay the WAL data into an isolated or restored target instance.
  4. Verify recovered devices, tables, time ranges, and business-level statistics.
  5. Archive the source WAL files and replay logs after validation.
  Example:
  tools/import-wal.sh \
    -f /path/to/wal \
    -h 127.0.0.1 \
    -p 6667 \
    -u root
  The implementation is available in PR #18516 (https://github.com/apache/iotdb/pull/18516). Feedback on the recovery workflow and operational usability would be very welcome.
  Best regards,
  Tian Jiang