Deletion Markers And TTL

ZoneTree uses deletion markers. A delete writes a new record that represents deletion, and compaction removes obsolete data later.

This is the normal model for LSM-tree storage engines. It lets deletes be fast writes instead of immediate expensive rewrites of older segments.

Delete APIs

UseTryDeletewhen you want to delete only if the key currently exists.

zoneTree.TryDelete(42, out var opIndex);

UseForceDeletewhen you want to write a deletion marker without checking older layers first.

zoneTree.ForceDelete(42);

ForceDeleteis faster, but it may create a deletion marker even when no older record exists.

Custom Deletion Logic

For many primitive and nullable types, ZoneTree can provide default deletion behavior. You can also define your own marker.

using var zoneTree = new ZoneTreeFactory<int, int>()
    .SetIsDeletedDelegate((in int key, in int value) => value == -1)
    .SetMarkValueDeletedDelegate((ref int value) => value = -1)
    .OpenOrCreate();

TTL

TTL can be modeled with the same mechanism. Store an expiration timestamp in the value and make the delete predicate returntrueafter expiration.

public readonly record struct CacheEntry(string Value, DateTime ExpiresAt);

using var zoneTree = new ZoneTreeFactory<string, CacheEntry>()
    .SetIsDeletedDelegate((in string key, in CacheEntry value) =>
        value.ExpiresAt <= DateTime.UtcNow)
    .SetMarkValueDeletedDelegate((ref CacheEntry value) =>
        value = value with { ExpiresAt = DateTime.MinValue })
    .OpenOrCreate();

Expired records are treated as deleted records. Maintenance and compaction can remove obsolete data later.

Disable Deletion

If your database does not need deletions and you want to store default values normally, disable deletion:

using var zoneTree = new ZoneTreeFactory<int, int>()
    .DisableDeletion()
    .OpenOrCreate();