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Disaster Recovery"><a href="Mnesia_chap7.html#id78876">Backup, Fallback, and Disaster Recovery</a></li> </ul> </li> <li id="no" title="Combining Mnesia with SNMP" expanded="false">Combining Mnesia with SNMP<ul> <li><a href="Mnesia_chap8.html"> Top of chapter </a></li> <li title="Combining Mnesia and SNMP "><a href="Mnesia_chap8.html#id79691">Combining Mnesia and SNMP </a></li> </ul> </li> <li id="no" title="Appendix A: Mnesia Error Messages" expanded="false">Appendix A: Mnesia Error Messages<ul> <li><a href="Mnesia_App_A.html"> Top of chapter </a></li> <li title="Errors in Mnesia"><a href="Mnesia_App_A.html#id79834">Errors in Mnesia</a></li> </ul> </li> <li id="no" title="Appendix B: The Backup Call Back Interface" expanded="false">Appendix B: The Backup Call Back Interface<ul> <li><a href="Mnesia_App_B.html"> Top of chapter </a></li> <li title="mnesia_backup callback behavior"><a href="Mnesia_App_B.html#id80051">mnesia_backup callback behavior</a></li> </ul> </li> <li id="no" title="Appendix C: The Activity Access Call Back Interface" expanded="false">Appendix C: The Activity Access Call Back Interface<ul> <li><a href="Mnesia_App_C.html"> Top of chapter </a></li> <li title="mnesia_access callback behavior"><a href="Mnesia_App_C.html#id80172">mnesia_access callback behavior</a></li> </ul> </li> <li id="loadscrollpos" title="Appendix D: The Fragmented Table Hashing Call Back Interface" expanded="true">Appendix D: The Fragmented Table Hashing Call Back Interface<ul> <li><a href="Mnesia_App_D.html"> Top of chapter </a></li> <li title="mnesia_frag_hash callback behavior"><a href="Mnesia_App_D.html#id80315">mnesia_frag_hash callback behavior</a></li> </ul> </li> </ul> </div></div> <div id="content"> <div class="innertube"> <h1>11 Appendix D: The Fragmented Table Hashing Call Back Interface</h1> <h3><a name="id80315">11.1 mnesia_frag_hash callback behavior</a></h3> <p></p> <div class="example"><pre> -module(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 ]). </pre></div> <p></p> <div class="example"><pre> -record(hash_state, {n_fragments, next_n_to_split, n_doubles, function}). %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% init_state(_Tab, State) when State == undefined -> #hash_state{n_fragments = 1, next_n_to_split = 1, n_doubles = 0, function = phash2}. convert_old_state({hash_state, N, P, L}) -> #hash_state{n_fragments = N, next_n_to_split = P, n_doubles = L, function = phash}. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% add_frag(#hash_state{next_n_to_split = SplitN, n_doubles = L, n_fragments = N} = State) -> P = SplitN + 1, NewN = N + 1, State2 = case power2(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]}; add_frag(OldState) -> State = convert_old_state(OldState), add_frag(State). %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% del_frag(#hash_state{next_n_to_split = SplitN, n_doubles = L, n_fragments = N} = State) -> P = SplitN - 1, if P < 1 -> L2 = L - 1, MergeN = power2(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; del_frag(OldState) -> State = convert_old_state(OldState), del_frag(State). %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% key_to_frag_number(#hash_state{function = phash, n_fragments = N, n_doubles = L}, Key) -> A = erlang:phash(Key, power2(L + 1)), if A > N -> A - power2(L); true -> A end; key_to_frag_number(#hash_state{function = phash2, n_fragments = N, n_doubles = L}, Key) -> A = erlang:phash2(Key, power2(L + 1)) + 1, if A > N -> A - power2(L); true -> A end; key_to_frag_number(OldState, Key) -> State = convert_old_state(OldState), key_to_frag_number(State, Key). %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% match_spec_to_frag_numbers(#hash_state{n_fragments = N} = State, MatchSpec) -> case MatchSpec of [{HeadPat, _, _}] when is_tuple(HeadPat), tuple_size(HeadPat) > 2 -> KeyPat = element(2, HeadPat), case has_var(KeyPat) of false -> [key_to_frag_number(State, KeyPat)]; true -> lists:seq(1, N) end; _ -> lists:seq(1, N) end; match_spec_to_frag_numbers(OldState, MatchSpec) -> State = convert_old_state(OldState), match_spec_to_frag_numbers(State, MatchSpec). power2(Y) -> 1 bsl Y. % trunc(math:pow(2, Y)). </pre></div> </div> <div class="footer"> <hr> <p>Copyright © 1997-2012 Ericsson AB. 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