Erlang:ets选择并匹配性能 [英] Erlang: ets select and match performance
问题描述
我发现函数ets:select / 2和mnesia:select / 3优于ets:match / 2,ets:match_object / 2和mnesia:match_object / 3 引用链接: http://www.erlang.org/doc/efficiency_guide/tablesDatabases.html
我读了一些有关选择和匹配之间进行比较的文章,得出结论,有一些因素会影响结果,例如表中的记录数量,选择/匹配主键与否,表类型(袋子,设置...)等。
And I'd read some essay about comparing between select and match, I conclude there are some factor effecting the result, such as records' amount in table, select/match a primary key or not, table kind(bag, set...), etc.
在我的测试中,我对所有功率为10W的表都适用记录和1W记录,并且只能选择/匹配非主键。
In my test, I do for all kind of table with 10W records and 1W records, and only select/match for a un-primary key.
以下代码:
select_ets_test(Times) ->
MS = ets:fun2ms(fun(T) when T#ets_haoxian_template.count == 15 -> T end),
T1 = timer:tc(?MODULE, todo, [fun() -> ets:select(haoxian_test_bag, MS) end, Times]),
T2 = timer:tc(?MODULE, todo, [fun() -> ets:select(haoxian_test_set, MS) end, Times]),
T3 = timer:tc(?MODULE, todo, [fun() -> ets:select(haoxian_test_ordered_set, MS) end, Times]),
T4 = timer:tc(?MODULE, todo, [fun() -> ets:select(haoxian_test_duplicate_bag, MS) end, Times]),
io:format("select bag : ~p~n", [T1]),
io:format("select set : ~p~n", [T2]),
io:format("select ordered_set : ~p~n", [T3]),
io:format("select duplicate bag : ~p~n", [T4]).
match_ets_test(Times) ->
MS = #ets_haoxian_template{count = 15, _ = '_' },
T1 = timer:tc(?MODULE, todo, [fun() -> ets:match_object(haoxian_test_bag, MS) end, Times]),
T2 = timer:tc(?MODULE, todo, [fun() -> ets:match_object(haoxian_test_set, MS) end, Times]),
T3 = timer:tc(?MODULE, todo, [fun() -> ets:match_object(haoxian_test_ordered_set, MS) end, Times]),
T4 = timer:tc(?MODULE, todo, [fun() -> ets:match_object(haoxian_test_duplicate_bag, MS) end, Times]),
io:format("match bag : ~p~n", [T1]),
io:format("match set : ~p~n", [T2]),
io:format("match ordered_set : ~p~n", [T3]),
io:format("match duplicate bag : ~p~n", [T4]).
todo(_Fun, 0) ->
ok;
todo(Fun, Times) ->
Fun(),
todo(Fun, Times - 1).
记录如下:#ets_haoxian_template {type = X,count = Y,...},关键姿势是类型。
the record would like: #ets_haoxian_template{type = X, count = Y, ...}, keypose is type.
以下结果:
1W测试:
the resule following: 1W test:
insert bag : {324000,true}
insert set : {221000,true}
insert ordered_set : {108000,true}
insert duplicate bag : {173000,true}
select bag : {284000,ok}
select set : {255000,ok}
select ordered_set : {221000,ok}
select duplicate bag : {252000,ok}
match bag : {238000,ok}
match set : {192000,ok}
match ordered_set : {136000,ok}
match duplicate bag : {191000,ok}
10W测试:
insert bag : {1654000,true}
insert set : {1684000,true}
insert ordered_set : {981000,true}
insert duplicate bag : {1769000,true}
select bag : {3404000,ok}
select set : {3433000,ok}
select ordered_set : {2501000,ok}
select duplicate bag : {3678000,ok}
match bag : {2749000,ok}
match set : {2927000,ok}
match ordered_set : {1748000,ok}
match duplicate bag : {2923000,ok}
似乎匹配比选择更好?还是我的测试有问题?
It seem match is better than select? Or my test something wrong???
推荐答案
match
函数使用特殊的元组语法( match_pattern
)决定返回什么。
The match
function employs a special tuple syntax (match_pattern
) to decide what to return.
select
函数采用特殊的元组语法(< a href = http://erlang.org/doc/man/ets.html#type-match_spec rel = nofollow noreferrer> match_spec
)这是 match_pattern
的超集,能够指定后卫并从结果集中提取元素(而不仅仅是返回匹配的键)。
The select
function employs a special tuple syntax (match_spec
) that is a superset of match_pattern
, with the ability to specify guards and extract elements from the result set (rather than just returning the matching keys).
我的理解是:
-
select
会编译match_spec
转换为匿名函数,从而加快了运行速度 - 为该函数提供防护的能力可以比以前更快地消除误报只需
match_pattern
(si (因为它们将首先运行) - 就地从结果集中提取元素的功能可以节省您以后要做的工作,而不是遍历返回的键来提取该数据
select
compiles thematch_spec
into an anonymous function, expediting how fast it runs- the ability to provide guards to this function eliminates false positives quicker than is possible with just a
match_pattern
(since they will run first) - the ability to extract elements from the result set in-place saves you work you would have to do later, rather than iterating over the returned keys to extract that data.
在琐碎的非特定用例中, select
只是一个匹配
的很多工作。在非平凡的更常见的用例中, select
会给您您真正想要的更快。
In trivial non-specific use-cases, select
is just a lot of work around match
. In non-trivial more common use-cases, select
will give you what you really want a lot quicker.
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