Storage Engine

The storage layer is page-native and built for deterministic flush/recovery behavior under pressure.

Buffer Pool Eviction/Flush Flow

+------------------------+
| fetch/new page         |
+------------------------+
            |
            v
+------------------------+
| pin frame in pool      |
+------------------------+
            |
            v
+------------------------+
| mutate page (dirty=1)  |
+------------------------+
            |
            v
+------------------------+
| unpin frame            |
+------------------------+
            |
            v
   +-------------------+
   | pressure present? |
   +-------------------+
      | yes       | no
      v           v
+----------------------+   +----------------------+
| choose LRU-K victim  |   | reuse frame/continue |
+----------------------+   +----------------------+
            |
            v
   +-------------------+
   | victim is dirty?  |
   +-------------------+
      | yes       | no
      v           v
+----------------------+   +----------------------+
| WAL flush_up_to(LSN) |   | evict victim         |
+----------------------+   +----------------------+
            |
            v
+----------------------+
| write page to disk   |
+----------------------+
            |
            v
+----------------------+
| evict victim         |
+----------------------+
            |
            v
+----------------------+
| reuse frame/continue |
+----------------------+

How EntDB uses storage components

• Page: fixed-size page with header/checksum, used as the stable on-disk unit.
• DiskManager: page allocation/deallocation and positioned I/O.
• BufferPool: in-memory frames with pin/unpin semantics, dirty tracking, and LRU-K victim selection.
• SlottedPage: tuple slot directory for variable-length row storage.
• Table: heap-page row layout plus tuple identity management.
• B+Tree: page-native index structure for point/range access.

What this is good for

• deterministic correctness under pressure,
• stable persistence format with reopen/recovery invariants,
• predictable behavior during eviction-heavy and crash-recovery scenarios.

Reference files

• crates/entdb/src/storage/page.rs
• crates/entdb/src/storage/disk_manager.rs
• crates/entdb/src/storage/buffer_pool.rs
• crates/entdb/src/storage/slotted_page.rs
• crates/entdb/src/storage/table.rs
• crates/entdb/src/storage/btree/tree.rs