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%% ``The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved via the world wide web at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% The Initial Developer of the Original Code is Ericsson Utvecklings AB.
%% Portions created by Ericsson are Copyright 1999, Ericsson Utvecklings
%% AB. All Rights Reserved.''
%%
%% $Id: mnesia_frag_hash.erl,v 1.1 2008/12/17 09:53:38 mikpe Exp $
%%
%%%----------------------------------------------------------------------
%%% Purpose : Implements hashing functionality for fragmented tables
%%%----------------------------------------------------------------------
%header_doc_include
-module(mnesia_frag_hash).
-behaviour(mnesia_frag_hash).
%% Fragmented Table Hashing callback functions
-export([
init_state/2,
add_frag/1,
del_frag/1,
key_to_frag_number/2,
match_spec_to_frag_numbers/2
]).
%header_doc_include
%impl_doc_include
-record(hash_state, {n_fragments, next_n_to_split, n_doubles}).
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
init_state(_Tab, State) when State == undefined ->
#hash_state{n_fragments = 1,
next_n_to_split = 1,
n_doubles = 0}.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
add_frag(State) when record(State, hash_state) ->
SplitN = State#hash_state.next_n_to_split,
P = SplitN + 1,
L = State#hash_state.n_doubles,
NewN = State#hash_state.n_fragments + 1,
State2 = case trunc(math:pow(2, L)) + 1 of
P2 when P2 == P ->
State#hash_state{n_fragments = NewN,
n_doubles = L + 1,
next_n_to_split = 1};
_ ->
State#hash_state{n_fragments = NewN,
next_n_to_split = P}
end,
{State2, [SplitN], [NewN]}.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
del_frag(State) when record(State, hash_state) ->
P = State#hash_state.next_n_to_split - 1,
L = State#hash_state.n_doubles,
N = State#hash_state.n_fragments,
if
P < 1 ->
L2 = L - 1,
MergeN = trunc(math:pow(2, L2)),
State2 = State#hash_state{n_fragments = N - 1,
next_n_to_split = MergeN,
n_doubles = L2},
{State2, [N], [MergeN]};
true ->
MergeN = P,
State2 = State#hash_state{n_fragments = N - 1,
next_n_to_split = MergeN},
{State2, [N], [MergeN]}
end.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
key_to_frag_number(State, Key) when record(State, hash_state) ->
L = State#hash_state.n_doubles,
A = erlang:phash(Key, trunc(math:pow(2, L))),
P = State#hash_state.next_n_to_split,
if
A < P ->
erlang:phash(Key, trunc(math:pow(2, L + 1)));
true ->
A
end.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
match_spec_to_frag_numbers(State, MatchSpec) when record(State, hash_state) ->
case MatchSpec of
[{HeadPat, _, _}] when tuple(HeadPat), size(HeadPat) > 2 ->
KeyPat = element(2, HeadPat),
case has_var(KeyPat) of
false ->
[key_to_frag_number(State, KeyPat)];
true ->
lists:seq(1, State#hash_state.n_fragments)
end;
_ ->
lists:seq(1, State#hash_state.n_fragments)
end.
%impl_doc_include
has_var(Pat) ->
mnesia:has_var(Pat).
|
