Pure OCaml B-tree implementation for persistent storage
Add transaction support to ocaml-sqlite
Add Pager.snapshot/rollback for capturing and restoring dirty page
state. Expose Table.save_root/restore_root and Index.save_root/
restore_root for B-tree root page rollback after splits.
Build Sqlite.with_transaction on top: snapshots pager state, B-tree
roots, and in-memory KV caches before running the user function. On
exception, all state is rolled back and the exception re-raised.
Five new tests cover commit, KV rollback, unique index rollback,
and nested transaction failure.
+74
+21
lib/btree.mli
+21
lib/btree.mli
···
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val sync : t -> unit
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(** [sync t] syncs all dirty pages to disk. *)
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type snapshot
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(** An opaque snapshot of pager state. *)
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val snapshot : t -> snapshot
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(** [snapshot t] captures the current dirty page set and page count. *)
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val rollback : t -> snapshot -> unit
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(** [rollback t snap] restores the pager to the state captured by [snap]. *)
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end
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(** {1 Table B-tree}
···
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val fold : t -> init:'a -> f:(int64 -> string -> 'a -> 'a) -> 'a
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(** [fold t ~init ~f] folds over all records in order. *)
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val save_root : t -> int
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(** [save_root t] returns the current root page for later restore. *)
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val restore_root : t -> int -> unit
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(** [restore_root t root] sets the root page to [root]. *)
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end
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(** {1 Index B-tree}
···
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val iter : t -> (string -> unit) -> unit
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(** [iter t f] calls [f key] for each key in sorted order. *)
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val save_root : t -> int
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(** [save_root t] returns the current root page for later restore. *)
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val restore_root : t -> int -> unit
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(** [restore_root t root] sets the root page to [root]. *)
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end
+3
lib/index.ml
+3
lib/index.ml
+6
lib/index.mli
+6
lib/index.mli
···
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val iter : t -> (string -> unit) -> unit
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(** [iter t f] calls [f key] for each key in sorted order. *)
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val save_root : t -> int
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(** [save_root t] returns the current root page for later restore. *)
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val restore_root : t -> int -> unit
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(** [restore_root t root] sets the root page to [root]. *)
+21
lib/pager.ml
+21
lib/pager.ml
···
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Eio.File.pwrite_all file ~file_offset:offset [ buf ])
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t.dirty);
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Hashtbl.clear t.dirty
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(* Snapshots *)
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type snapshot = { s_dirty : (int, string) Hashtbl.t; s_page_count : int }
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let snapshot t = { s_dirty = Hashtbl.copy t.dirty; s_page_count = t.page_count }
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let rollback t snap =
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(* Invalidate cache for pages dirtied since the snapshot *)
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Hashtbl.iter
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(fun page _ ->
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if not (Hashtbl.mem snap.s_dirty page) then Hashtbl.remove t.cache page)
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t.dirty;
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(* Restore dirty set and update cache from snapshot *)
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Hashtbl.reset t.dirty;
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Hashtbl.iter
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(fun k v ->
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Hashtbl.replace t.dirty k v;
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Hashtbl.replace t.cache k v)
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snap.s_dirty;
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t.page_count <- snap.s_page_count
+14
lib/pager.mli
+14
lib/pager.mli
···
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val sync : t -> unit
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(** [sync t] syncs all dirty pages to disk. *)
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(** {1 Snapshots}
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Snapshots capture the pager state for transaction rollback. *)
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type snapshot
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(** An opaque snapshot of pager state. *)
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val snapshot : t -> snapshot
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(** [snapshot t] captures the current dirty page set and page count. *)
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val rollback : t -> snapshot -> unit
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(** [rollback t snap] restores the pager to the state captured by [snap]. Pages
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modified since the snapshot are discarded from the dirty set and cache. *)
+3
lib/table.ml
+3
lib/table.ml
+6
lib/table.mli
+6
lib/table.mli
···
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val fold : t -> init:'a -> f:(int64 -> string -> 'a -> 'a) -> 'a
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(** [fold t ~init ~f] folds over all records in order. *)
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val save_root : t -> int
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(** [save_root t] returns the current root page for later restore. *)
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val restore_root : t -> int -> unit
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(** [restore_root t root] sets the root page to [root]. *)