[erlnag] ETS & DETS

erlang提供的k-v存储　ets保存在内存里　dets保存在磁盘上

ETS表与正常的进程存储空间是分离的,其存储区域与普通进程无关,ETS表隶属于创建它的进程,当这个进程死掉或者调用了ets:delete,ETS表就被删掉了

测试&示例代码

-module(test_ets).
-compile(export_all).

start() ->
    %% 4种不同表的类型
    lists:foreach(fun test/1,[set,ordered_set,bag,duplicate_bag]).

test(Mode) ->
    %% 表类型 set,ordered_set,bag,duplicate_bag 
    %% 访问控制 private,protected,public
    %% named_table 后续操作使用tablename来操作 如 ets:inert(tablename,{a,1234}).
    TableId = ets:new(tablename,[Mode,named_table]),
    ets:insert(TableId,{a,1}),
    ets:insert(TableId,{b,2}),
    ets:insert(tablename,{a,1}), %% 使用tablename
    ets:insert(TableId,{a,3}),
    List = ets:tab2list(tablename),
    io:format("~-13w => ~p~n",[Mode,List]),
    ets:delete(tablename).

test_new() ->
    ets:new(tablename,[set,public,named_table]).

test_insert(Key,Value) ->
    ets:insert(tablename,{Key,Value}).

test_lookup(Key) ->
    ets:lookup(tablename,Key).

test_delete() ->
    ets:delete(tablename).

%% dets
%% 文件大小不能超过2G
open(File) ->
    io:format("dets opened:~p~n",[File]),
    Bool = filelib:is_file(File),
    case dets:open_file(?MODULE,[{file,File}]) of
        {ok,?MODULE} ->
            case Bool of
                true -> void;
                false -> ok = dets:insert(?MODULE,{free,1})
            end,
            true;
        {error,Reason} ->
            io:format("cannot open dets table:~p~n",[Reason]),
            exit(eDetsOpen)
    end.

close() -> dets:close(?MODULE).

test_dets_insert(Key,Value) ->
    dets:insert(?MODULE,{Key,Value}).

test_dets_lookup(Key) ->
    dets:lookup(?MODULE,Key).

运行结果

Eshell V5.8.4  (abort with ^G)
1> c(test_ets).
{ok,test_ets}
2> test_ets:start().
set           => [{b,2},{a,3}]
ordered_set   => [{a,3},{b,2}]
bag           => [{b,2},{a,1},{a,3}]
duplicate_bag => [{b,2},{a,1},{a,1},{a,3}]
ok
3> T = ets:new(test,[public,set]).
32784
4> ets:insert(T,{key,23456}).
true
5> ets:lookup(T,key).        
[{key,23456}]
6> c(test_ets).                   
{ok,test_ets}
7> test_ets:open("test.bin").     
dets opened:"test.bin"
true
8> test_ets:test_dets_insert(a,b).
ok
9> test_ets:test_dets_lookup(a).  
[{a,b}]