Reliability and Recovery

EntDB durability and restart safety are driven by WAL-first write semantics and deterministic recovery.

Durability policy is configurable at runtime:

Full: strict sync on commit path
Normal: reduced sync pressure with the same recovery model
Off: best-effort durability for ephemeral workloads

Callers that normally run in Normal or Off can still force a durable boundary on a specific operation.

Reliability stack

WAL record checksums and replay safety,
analysis/redo/undo recovery paths,
failpoint and crash-point matrices,
idempotent recovery expectations.

WAL Recovery Flow

+------------------------------+
| startup                      |
+------------------------------+
               |
               v
+------------------------------+
| scan WAL records             |
+------------------------------+
               |
               v
+------------------------------+
| analysis                     |
| - collect txn states         |
| - collect touched pages      |
+------------------------------+
               |
               v
+------------------------------+
| redo                         |
| - replay committed updates   |
| - respect page LSN checks    |
+------------------------------+
               |
               v
+------------------------------+
| undo                         |
| - roll back incomplete txns  |
+------------------------------+
               |
               v
+------------------------------+
| consistent recovered state   |
+------------------------------+

Validation coverage

Reliability behavior is validated with crash matrices, failpoint-driven recovery tests, and MVCC restart visibility tests.

What this protects

committed transactions remain visible across restart,
incomplete/aborted transactions do not leak visibility,
repeated recovery runs converge to the same state.
durability policy changes trade commit latency against sync strictness, not MVCC visibility rules.

Reference files

crates/entdb/src/wal/log_record.rs
crates/entdb/src/wal/log_manager.rs
crates/entdb/src/wal/recovery.rs
crates/entdb/src/wal/tests/recovery_tests.rs
crates/entdb/tests/crash_matrix.rs