Module pager 

On-disk persistence for a Database, using fixed-size paged files.

The file is a sequence of 4 KiB pages. Page 0 holds the header (magic, version, page count, schema-root pointer). Every other page carries a small per-page header (type tag + next-page pointer + payload length) followed by a payload of up to 4089 bytes.

Storage strategy (format version 2, Phase 3c.5).

• Each Table’s rows live as cells in a chain of TableLeaf pages. Cell layout and slot directory are in cell.rs / table_page.rs; cells that exceed the inline threshold spill into an overflow chain via overflow.rs.
• The schema catalog is itself a regular table named sqlrite_master, with one row per user table: (name TEXT PRIMARY KEY, sql TEXT NOT NULL, rootpage INTEGER NOT NULL, last_rowid INTEGER NOT NULL) This is the SQLite-style approach: the schema of sqlrite_master itself is hardcoded into the engine so the open path can bootstrap.
• Page 0’s schema_root_page field points at the first leaf of sqlrite_master.

Format version. Version 2 is not compatible with files produced by earlier commits. Opening a v1 file returns a clean error — users on old files have to regenerate them from CREATE/INSERT, as there’s no production data to migrate yet.

Re-exports

pub use crate::sql::pager::pager::AccessMode;

Modules

cell

Cell format: one row per cell, hand-rolled length-prefixed encoding.

file

Page-indexed file I/O: read/write whole pages by page number, plus the special page-0 header. Deliberately thin — this is the only place that touches std::fs, so higher layers deal in pages, not offsets.

header

Database file header (page 0).

index_cell

On-disk format for a single secondary-index entry.

interior_page

Interior B-Tree page layout.

overflow

Overflow storage for cells that don’t fit on one table-leaf page.

page

Page layout primitives.

pager

Long-lived page cache + WAL-backed commits.

table_page

Table-leaf page layout: a slot directory + cell content.

varint

Variable-length integer encoding.

wal

Write-Ahead Log (WAL) file format.

Constants

MASTER_TABLE_NAME

Name of the internal catalog table. Reserved — user CREATEs of this name must be rejected upstream.

Functions

open_database

Opens a database file in read-write mode. Shorthand for open_database_with_mode with AccessMode::ReadWrite.

open_database_read_only

Opens a database file in read-only mode. Acquires a shared OS-level advisory lock, so other read-only openers coexist but any writer is excluded. Attempts to mutate the returned Database (e.g. an INSERT, or a save_database call against it) bottom out in a cannot commit: database is opened read-only error from the Pager.

open_database_with_mode

Opens a database file and reconstructs the in-memory Database, leaving the long-lived Pager attached for subsequent auto-save (read-write) or consistent-snapshot reads (read-only).

save_database

Persists db to disk. Same diff-commit behavior as before: only pages whose bytes actually changed get written.