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open Relational_engine
(* Content-addressed store: hash -> bytes. In production this is NT storage. *)
let store : (string, bytes) Hashtbl.t = Hashtbl.create 64
(* --- Object construction helpers --- *)
let make_tuple ~relation attributes =
let attr_map =
List.fold_left
(fun acc (name, value) ->
Tuple.AttributeMap.add name
{ Attribute.value = Obj.repr (value : string) }
acc)
Tuple.AttributeMap.empty attributes
in
{ Tuple.relation; attributes = attr_map }
(* Simulate B+ tree root: hash of sorted tuple hashes. *)
let tuple_tree_pointer tuples =
List.map Hashing.hash_tuple tuples
|> List.sort String.compare
|> List.fold_left ( ^ ) ""
|> Conventions.Hash.hash_text
let make_relation ~name ~schema ~cardinality tuples =
(new Relation.stored
~name ~schema ~constraints:None
~cardinality:(Conventions.Cardinality.Finite cardinality)
~membership_criteria:(fun _ -> true)
~lineage:None ~provenance:None)
#set_tree_pointer (Some (tuple_tree_pointer tuples))
(* --- Persistence layer (writing into the store) --- *)
let persist_tuple tuple =
let hash = Hashing.hash_tuple tuple in
Hashtbl.add store hash (Marshal.to_bytes tuple [ Marshal.Closures ]);
hash
(* Store an ordered list of child hashes at a tree node address. *)
let persist_tree_node node_hash (child_hashes : string list) =
Hashtbl.add store node_hash (Marshal.to_bytes child_hashes [])
(* Store a relation's metadata (name, schema, tree_pointer) at its hash. *)
let persist_relation (rel : Relation.stored) =
Hashtbl.add store rel#hash
(Marshal.to_bytes (rel#name, rel#schema, rel#tree_pointer) [])
(* --- Reconstruction layer (reading from the store) --- *)
let load : 'a. string -> 'a = fun hash ->
Marshal.from_bytes (Hashtbl.find store hash) 0
let reconstruct_from_tree_pointer mg_tp =
let rel_hashes : string list = load mg_tp in
List.map (fun rel_hash ->
let (name, schema, tp_opt) : string * Schema.t * string option =
load rel_hash
in
let tuples : Tuple.materialized list =
match tp_opt with
| None -> []
| Some tp ->
let tuple_hashes : string list = load tp in
List.map load tuple_hashes
in
(name, schema, tuples)
) rel_hashes
(* --- Printing --- *)
let print_tuple (t : Tuple.materialized) =
let fields =
Tuple.AttributeMap.bindings t.attributes
|> List.map (fun (k, attr) ->
k ^ " = " ^ (Obj.magic attr.Attribute.value : string))
|> String.concat ", "
in
Printf.printf " { %s }\n" fields
let print_reconstructed relations =
List.iter (fun (name, schema, tuples) ->
Printf.printf " relation: %s [%s]\n"
name
(String.concat ", " (List.map (fun (a, d) -> a ^ ":" ^ d) schema));
List.iter print_tuple tuples
) relations
(* --- Main --- *)
let boot () =
(* Tuples *)
let dept_engineering =
make_tuple ~relation:"departments" [ ("id", "1"); ("name", "Engineering") ]
in
let dept_sales =
make_tuple ~relation:"departments" [ ("id", "2"); ("name", "Sales") ]
in
let emp_alice =
make_tuple ~relation:"employees"
[ ("dept_id", "1"); ("id", "1"); ("name", "Alice") ]
in
let emp_bob =
make_tuple ~relation:"employees"
[ ("dept_id", "2"); ("id", "2"); ("name", "Bob") ]
in
(* Persist tuples and capture their hashes *)
let dept_eng_hash = persist_tuple dept_engineering in
let dept_sales_hash = persist_tuple dept_sales in
let emp_alice_hash = persist_tuple emp_alice in
let emp_bob_hash = persist_tuple emp_bob in
(* Build relations with tree_pointers derived from tuple hashes *)
let departments =
make_relation
~name:"departments"
~schema:[ ("id", "int"); ("name", "string") ]
~cardinality:2
[ dept_engineering; dept_sales ]
in
let employees =
make_relation
~name:"employees"
~schema:[ ("id", "int"); ("name", "string"); ("dept_id", "int") ]
~cardinality:2
[ emp_alice; emp_bob ]
in
(* Persist each relation's B+ tree node (tuple hashes) at its tree_pointer *)
let dept_tp = Option.get departments#tree_pointer in
let emp_tp = Option.get employees#tree_pointer in
persist_tree_node dept_tp
(List.sort String.compare [ dept_eng_hash; dept_sales_hash ]);
persist_tree_node emp_tp
(List.sort String.compare [ emp_alice_hash; emp_bob_hash ]);
(* Persist relation metadata at each relation hash *)
persist_relation departments;
persist_relation employees;
(* Build multigroup *)
let company =
List.fold_left
(fun mg rel -> mg#add_relation rel)
(new Management.Multigroup.multigroup ~name:"company")
[ (departments :> Relation.relation); (employees :> Relation.relation) ]
in
(* Persist multigroup's B+ tree node (relation hashes) at its tree_pointer *)
let mg_tp = Option.get company#tree_pointer in
persist_tree_node mg_tp
(List.sort String.compare [ departments#hash; employees#hash ]);
Printf.printf "=== Built state ===\n";
Printf.printf " multigroup hash: %s\n" company#hash;
Printf.printf " tree_pointer: %s\n\n" mg_tp;
(* Drop everything except the tree_pointer and reconstruct *)
Printf.printf "=== Reconstructing from tree_pointer only ===\n";
let relations = reconstruct_from_tree_pointer mg_tp in
print_reconstructed relations
let () = boot ()
|
