Pure OCaml B-tree implementation for persistent storage
btree: Format code
+22
-7
+22
-7
lib/btree.ml
+22
-7
lib/btree.ml
···
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in
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find 0
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-
(* Find child page for rowid in interior page *)
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+
(* Find child page for rowid in interior page.
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SQLite B-tree: keys < separator go left, keys >= separator go right. *)
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let find_child _t page header rowid =
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let ptrs = cell_pointers page 0 header in
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let rec loop i =
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if i >= header.cell_count then Option.get header.right_child
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else
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let cell, _ = Cell.parse_table_interior page ptrs.(i) in
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-
if rowid <= cell.rowid then cell.left_child else loop (i + 1)
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if rowid < cell.rowid then cell.left_child else loop (i + 1)
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in
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loop 0
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···
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if i >= header.cell_count then i (* right child *)
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else
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let cell, _ = Cell.parse_table_interior page ptrs.(i) in
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-
if rowid <= cell.rowid then i else loop (i + 1)
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+
if rowid < cell.rowid then i else loop (i + 1)
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in
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loop 0
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···
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(* Need to split *)
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let split = split_leaf t page_num in
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-
(* Insert into appropriate page *)
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if rowid < split.separator_rowid then
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insert_into_leaf t page_num ~rowid ~data ~parent_stack:[]
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-
else insert_into_leaf t split.new_page ~rowid ~data ~parent_stack:[];
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(* Determine target page and insert directly (no recursion needed -
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after split, both pages have ~half capacity, plenty of room) *)
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let target_page =
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if rowid < split.separator_rowid then page_num else split.new_page
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in
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let target = Pager.read t.pager target_page in
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let target_header = parse_page_header target 0 in
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let target_buf = Bytes.of_string target in
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let insert_idx = find_insert_idx t target target_header rowid in
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+
let cell_start =
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write_cell target_buf
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+
~cell_content_start:target_header.cell_content_start ~cell
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+
in
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+
set_u16_be target_buf 5 cell_start;
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insert_cell_pointer target_buf ~header_offset:0 ~page_type:Leaf_table
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~cell_count:target_header.cell_count ~index:insert_idx ~ptr:cell_start;
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set_u16_be target_buf 3 (target_header.cell_count + 1);
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Pager.write t.pager target_page (Bytes.unsafe_to_string target_buf);
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(* Propagate split up *)
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propagate_split t ~parent_stack ~left_page:page_num