FortDB — Fully Versioned, Crash‑Proof, Hierarchical NoSQL Database Interactive Shell Usage

1. Start FortDB

   $ ./fortdb
   fortdb started. Type 'exit' or 'quit' to quit.
   fortdb>

2. Supported Commands

   Command	Example	Description
   load <path>	load /home/me/db.fort	Load database from file
   get <path> [--v=<V>]	get users/john/age	Fetch field value (optional local version V)
   set <path> <value>	set users/john/age 42	Insert or update field
   delete <path>	delete users/john/age	Tombstone an entity
   list-versions <path>	list-versions users/john/age	List all versions of an entity
   compact <path>	compact users/john	Retain only latest versions, remove tombstones
   compact_db	compact_db	Compact entire database
   save <path>	save ./test/saves/db.fort	Save current in-memory DB to file
   exit, quit	exit	Exit the interactive shell
   dump	dump	Print the entire database state to the console
   help, ?	help	Show this help message

3. Key Features

• Append-only writes: SET/DELETE always append; no in-place updates, ensuring crash safety.
• Hierarchical versioning: VersionNode chains at every level.
• Local versions: uint64_t counters track per-entity changes.
• Time-travel reads: Query any historical state with --v flag.
• Atomic compaction: Background process compacts data and swaps files atomically.
• Thread-safe: RW-locks on structures and global mutex for version counter.

4. Example Session

$ ./fortdb
fortdb started. Type 'exit' or 'quit' to quit.
fortdb> load db.fort
Loaded database from db.fort
fortdb> get users/alice/email
alice@example.com
fortdb> get users/alice 
fields: name, age
subdocuments: children
fortdb> set users/alice/age 30
OK
fortdb> list-versions users/alice/age
v3: 30
v2: <deleted>
v1: 29
fortdb> compact users/alice
Compacted users/alice
fortdb> save db.fort
Saved database to db.fort
fortdb> exit

5. Getting Help

Type help at the prompt for command summaries.