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-module(poc).
-export([test/0, setup/0]).
test() ->
io:format("~nVolcano Iterator~n~n"),
%% Setup in-memory "database" (simulating Mnesia)
io:format("Setting up content-addressed storage...~n"),
Storage = setup(),
%% Insert data with automatic deduplication
io:format("Inserting products (note 'Soap' is stored only once)...~n"),
{Storage2, SoapHash} = store_value(Storage, "Soap"),
{Storage3, Price1Hash} = store_value(Storage2, 1.0),
{Storage4, BazookaHash} = store_value(Storage3, "Bazooka"),
{Storage5, Price2Hash} = store_value(Storage4, 413.0),
{Storage6, _SoapHash2} = store_value(Storage5, "Soap"), % Duplicate on purpose
{Storage7, Price3Hash} = store_value(Storage6, 50.0),
io:format("Unique values stored: ~p~n", [maps:size(maps:get(values, Storage7))]),
io:format("(Expected: 5, not 6 becase 'Soap' got deduplicated)~n~n"),
Tuple1 = #{name => SoapHash, price => Price1Hash},
Tuple2 = #{name => BazookaHash, price => Price2Hash},
Tuple3 = #{name => SoapHash, price => Price3Hash},
Tuples = [Tuple1, Tuple2, Tuple3],
io:format("Created 3 product tuples (referencing hashes)~n"),
io:format("Tuple1: #{name => ~s, price => ~s}~n",
[short_hash(SoapHash), short_hash(Price1Hash)]),
io:format("Tuple2: #{name => ~s, price => ~s}~n",
[short_hash(BazookaHash), short_hash(Price2Hash)]),
io:format("Tuple3: #{name => ~s, price => ~s}~n~n",
[short_hash(SoapHash), short_hash(Price3Hash)]),
io:format("Building query pipeline (Volcano Model):~n"),
io:format("Scan -> SELECT(price =< 100) -> Project(name)~n~n"),
ScanPid = spawn(fun() -> scan_iterator(Tuples, Storage7) end),
SelectPid = spawn(fun() ->
select_iterator(ScanPid, Storage7, fun(#{price := P}) -> P =< 100.0 end)
end),
ProjectPid = spawn(fun() ->
project_iterator(SelectPid, [name])
end),
io:format("Pulling results (on-demand, lazy evaluation):~n"),
Results = pull_all(ProjectPid),
io:format("~n"),
lists:foreach(fun(#{name := Name}) ->
io:format("-> #{name => ~p}~n", [Name])
end, Results),
ok.
setup() ->
#{values => #{}}. % Hash => Value map
store_value(Storage, Value) ->
Hash = value_hash(Value),
Values = maps:get(values, Storage),
case maps:is_key(Hash, Values) of
true ->
io:format("[DEDUP] Value ~p already exists (hash: ~s)~n",
[Value, short_hash(Hash)]),
{Storage, Hash};
false ->
io:format("[STORE] Value ~p (hash: ~s)~n",
[Value, short_hash(Hash)]),
NewValues = maps:put(Hash, Value, Values),
{Storage#{values => NewValues}, Hash}
end.
get_value(Storage, Hash) ->
Values = maps:get(values, Storage),
maps:get(Hash, Values).
value_hash(Value) ->
%% Simple hash for demo (in production: crypto:hash(sha256, term_to_binary(Value)))
erlang:phash2(Value).
short_hash(Hash) ->
lists:flatten(io_lib:format("~8.16.0B", [Hash])).
scan_iterator([], _Storage) ->
receive
{next, Caller} -> Caller ! done
end;
scan_iterator([TupleWithHashes | Rest], Storage) ->
receive
{next, Caller} ->
%% Unpacks all the hashes from each tuple
%% later we gotta use this on the merkle tree
%% for now it's just silly and inneficient
ResolvedTuple = maps:map(fun(_Attr, Hash) ->
get_value(Storage, Hash)
end, TupleWithHashes),
io:format("[SCAN] Emitting tuple: ~p~n", [ResolvedTuple]),
Caller ! {tuple, ResolvedTuple},
scan_iterator(Rest, Storage)
end.
select_iterator(SourcePid, Storage, Predicate) ->
receive
{next, Caller} ->
SourcePid ! {next, self()},
receive
done ->
Caller ! done;
{tuple, Tuple} ->
case Predicate(Tuple) of
true ->
io:format("[SELECT] Pass: ~p~n", [Tuple]),
Caller ! {tuple, Tuple},
select_iterator(SourcePid, Storage, Predicate);
false ->
io:format("[SELECT] Reject: ~p~n", [Tuple]),
%% Ignore this dude, and lock the process again
select_iterator_loop(SourcePid, Storage, Predicate, Caller)
end
end
end.
select_iterator_loop(SourcePid, Storage, Predicate, Caller) ->
SourcePid ! {next, self()},
receive
done ->
Caller ! done;
{tuple, Tuple} ->
case Predicate(Tuple) of
true ->
io:format("[SELECT] Pass: ~p~n", [Tuple]),
Caller ! {tuple, Tuple},
select_iterator(SourcePid, Storage, Predicate);
false ->
io:format("[SELECT] Reject: ~p~n", [Tuple]),
select_iterator_loop(SourcePid, Storage, Predicate, Caller)
end
end.
project_iterator(SourcePid, Attributes) ->
receive
{next, Caller} ->
SourcePid ! {next, self()},
receive
done ->
Caller ! done;
{tuple, Tuple} ->
ProjectedTuple = maps:with(Attributes, Tuple),
io:format("[PROJECT] ~p -> ~p~n", [Tuple, ProjectedTuple]),
Caller ! {tuple, ProjectedTuple},
project_iterator(SourcePid, Attributes)
end
end.
pull_all(IteratorPid) ->
pull_all(IteratorPid, []).
pull_all(IteratorPid, Acc) ->
IteratorPid ! {next, self()},
receive
done ->
lists:reverse(Acc);
{tuple, Tuple} ->
pull_all(IteratorPid, [Tuple | Acc])
after 1000 ->
{error, timeout}
end.
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