Module segment 

WAL segment management.

The WAL is split into fixed-size segment files for efficient truncation. Each segment is a standalone WAL file containing records within an LSN range.

Naming convention

Segments are named wal-{first_lsn:020}.seg — zero-padded for lexicographic ordering. This guarantees ls and readdir return segments in LSN order.

Lifecycle

1. Writer creates a new segment when the current segment exceeds target_size.
2. The active segment is the one being appended to.
3. truncate_before(lsn) deletes all sealed segments whose max_lsn < lsn.
4. The active segment is NEVER deleted — only sealed (closed) segments are eligible.

Recovery

On startup, all segment files in the WAL directory are discovered via readdir, sorted by first_lsn, and replayed in order. The last segment is the active one.

Re-exports

pub use atomic_io::atomic_swap_dirs_fsync;

pub use atomic_io::atomic_write_fsync;

pub use atomic_io::fsync_directory;

pub use atomic_io::read_checkpoint_dontneed;

pub use discovery::discover_segments;

pub use meta::DEFAULT_SEGMENT_TARGET_SIZE;

pub use meta::SegmentMeta;

pub use meta::segment_filename;

pub use meta::segment_path;

pub use migration::migrate_legacy_wal;

pub use truncate::TruncateResult;

pub use truncate::truncate_segments;

Modules

atomic_io

Durable atomic file / directory operations for checkpoint-class writes.

discovery

Discovery of WAL segment files in a directory.

meta

Segment filename conventions and on-disk metadata.

migration

One-time migration from legacy single-file WAL to segmented layout.

truncate

Sealed segment truncation after checkpoint LSN advances.