Expose exact transaction log positions

[ronag]

Summary

• expose WAL file, logical-record offset/end, and optional XXH3 checksum on each BatchResult
• keep checksum calculation disabled by default and opt in through TransactionLogIterator::ReadOptions
• make complete zero-count/log-data records visible at the current WAL tail
• retain an in-flight consuming record until its complete sequence range is published
• document clean-tail continuation and preserve cursor metadata across moves

This intentionally targets the v11.1.1 maintenance branch created from the exact RocksDB version consumed by nxtedition/rocks-level. No upstream PR is opened.

Validation

• make -j8 db_log_iter_test CC='ccache clang' CXX='ccache clang++'
• ./db_log_iter_test (11/11)
• focused log-only tail, initial-sequence, and unpublished-record tests (3/3)
• git diff --check

[Copilot]

Pull request overview

This PR extends RocksDB’s transaction log iterator to expose stable, exact WAL positioning metadata (WAL file number, logical record start/end offsets, and XXH3 checksum) via TransactionLogIterator::BatchResult, and updates iterator behavior to make log-data-only tail records visible and resumable while preserving cursor metadata across tailing.

Changes:

• Add WAL position + checksum fields to BatchResult and propagate them from the WAL reader.
• Adjust transaction log iteration so zero-count (e.g., log-data-only) records are visible at a clean WAL tail, and consuming records aren’t exposed until their full sequence range is published.
• Add unit tests covering log-data-only tail behavior, WAL position/checksum propagation, and unpublished consuming-record visibility; add a new SyncPoint in the write path to support the test.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
include/rocksdb/transaction_log.h	Extends public BatchResult with WAL location + checksum fields; clarifies iterator tailing semantics in comments.
db/transaction_log_impl.h	Adds internal state to track per-record WAL metadata and buffer unpublished consuming records until published.
db/transaction_log_impl.cc	Implements publication gating, captures WAL offsets/checksum from log::Reader, and propagates metadata to BatchResult.
db/db_log_iter_test.cc	Adds tests for log-data-only tail visibility, WAL position/checksum, and unpublished consuming-record gating.
db/db_impl/db_impl_write.cc	Adds a SyncPoint after WAL write to deterministically test unpublished consuming-record behavior.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

[ronag]

Closing this approach because it requires modifying RocksDB. I am replacing it with a rocks-level-only implementation against the unchanged v11.1.1 dependency.