[mnesia]mnesia内存备份表存储数据总结

　　今天群里有一朋友(随波逐流磨剑)提了这么一个问题说并行写入时数据丢失，当然最后的原因是他没等所有写入进程执行完就进行查询，所以数据自然少了，不过这不是我要说的重点，重点是我在帮他测试程序的时候遇到了一个警告和一个错误：

警告：** WARNING ** Mnesia is overloaded: {mnesia_tm, message_queue_len, [2107,1441]}

错误：** Too many db tables **

代码：

-module(test_mnesia).
%%-include("test_mnesia.hrl").

-export([init/0,insert_recodes/2,select/0,select2/0,clear/0]).
-record(hdjsw, {id, bei_bao, ci_shu, fu_jian, jie_shu_date, sheng_cheng_date, shi_yong_date, bian_hao}).
-record(hdjoin, {id, hdjsw, name, type}).

init() ->

%spawn(fun()-> randoms:start() end),

case mnesia:create_schema([node()]) of
ok ->
ok;
_ ->
mnesia:delete_schema([node()]),
mnesia:create_schema([node()])
end,

mnesia:start(),

case mnesia:create_table(hdjsw,[{ram_copies, []},{type, bag},{attributes, record_info(fields,hdjsw)}]) of
{atomic, ok} ->
ok;
_Any1 ->
mnesia:delete_table(hdjsw),
mnesia:create_table(hdjsw,[{ram_copies, []},{type, bag},{attributes, record_info(fields,hdjsw)}])
end,

case mnesia:create_table(hdjoin,[{ram_copies, []},{type, bag},{attributes, record_info(fields,hdjoin)}]) of
{atomic, ok} ->
ok;
_Any2 ->
mnesia:delete_table(hdjoin),
mnesia:create_table(hdjoin,[{ram_copies, []},{type, bag},{attributes, record_info(fields,hdjoin)}])
end.

%	mnesia:create_table(hdjsw,[{ram_copies, []},{attributes, record_info(fields,hdjsw)}]),
%	mnesia:create_table(hdjoin,[{ram_copies, []},{attributes, record_info(fields,hdjoin)}]).

insert_recodes(N,T) ->%200000,2000
C = trunc(N/T),%100
M = N rem T,%0
case C of
0 ->
spawn_insert_recode(N,1);
_ ->
spawn_insert_recode(T,C),
spawn_insert_recode(M,1)
end.

spawn_insert_recode(0,_) ->
ok;
spawn_insert_recode(N,M) ->%{2000, 100},{500,1}
spawn(fun()-> insert_recode(M) end),
spawn_insert_recode(N-1,M).

insert_recode(0) ->
ok;
insert_recode(N) ->%10

Hdjsw = #hdjsw{id=get_string(),
bei_bao = "dsg",
ci_shu = "asdhg",
fu_jian = "adfsh",
jie_shu_date = "sadhged",
sheng_cheng_date = 44,
shi_yong_date = "dsfh",
bian_hao = 54},
Fun = fun() ->
mnesia:write(Hdjsw),
insert(Hdjsw,10)
end,
%spawn(fun()-> mnesia:transaction(Fun) end),
mnesia:transaction(Fun),
insert_recode(N-1).

insert(_Hdjsw,0) ->
ok;
insert(Hdjsw,N) ->
Hdjoin = #hdjoin{
id = get_string(),
hdjsw = Hdjsw,
name = hdjswname,
type = 2
},
mnesia:write(Hdjoin),
insert(Hdjsw,N-1).

select() ->
F = fun() ->
Q = #hdjsw{id = '$1', _ = '_'},
mnesia:select(hdjsw, [{Q, [], ['$1']}])
end,
{atomic, L} = mnesia:transaction(F),
length(L).

select2() ->
F = fun() ->
Q = #hdjoin{id = '$1', _ = '_'},
mnesia:select(hdjoin, [{Q, [], ['$1']}])
end,
{atomic, L} = mnesia:transaction(F),
length(L).

clear() ->
mnesia:clear_table(hdjsw),
mnesia:clear_table(hdjoin).

get_string() ->
{M, S, L} = now(),
integer_to_list(M*1000000000000+S*1000000+L).