4

我有以下 Oracle 表：

create table my_table(
   start int,
   end int
);

insert into my_table values(1, 3);
insert into my_table values(5, 7);
insert into my_table values(11, 200);
insert into my_table values(311, 5000);
insert into my_table values(60004, 60024);
insert into my_table values(123213, 12312312);

该表有 1M 行并存储数字范围（'start'，'end'），所有数字都是唯一的，它没有重复的范围，任何数字只能在此表中的一个范围内，我有以下查询通过变量 my_number 来标识范围的“开始”。

 execute immediate 
    'select start from my_table where :1 between start and end' using my_number

我已经在这两个字段上建立了组合索引。问题是当my_number 小时，查询性能很好，但是当my_number 增加时，查询时间不断增加。如果 my_number 大得多，则需要相当长的时间才能完成。有人有办法改进这个查询吗？方法可以包括重新设计 my_table。谢谢。

4

5 回答 5

2

如果您将架构更改为此：

create table my_table(
   start int,
   range_size int
);

insert into my_table values(1, 2);
insert into my_table values(5, 2);
insert into my_table values(11, 189);
insert into my_table values(311, 4689);
insert into my_table values(60004, 20);
insert into my_table values(123213, 12300001);

然后你可以只在start列上建立索引。

execute immediate 
    'select start from (select start, range_size from my_table where start < :1 order by start asc limit 1) tmp where :1 < start+range_size' using my_number

这可能会有一些性能提升。

于 2013-04-04T18:02:04.963 回答
0

你这样做了吗？

create table my_table(
start int,
end int
constraint PK_comp primary key (start, end)
) ;
于 2013-04-04T18:03:35.220 回答
0

为每一列创建一个索引并使用这个查询：

select start_num
from my_table
where
    start_num =
    (
        --Last start <= number
        select start_num
        from
        (
            select start_num
            from my_table
            where :1 >= start_num
            order by start_num desc
        )
        where rownum = 1
    ) and
    end_num =
    (
        --First end >= number
        select end_num
        from
        (
            select end_num
            from my_table
            where :1 <= end_num
            order by end_num
        )
        where rownum = 1
    );

呸。可能有更好的方法来写这个。或者您可能希望将其包装在一个函数中。

问题

测试数据（带有非保留字列名）：

drop table my_table;
create table my_table(
   start_num int,
   end_num int
);
insert into my_table select level*2,level*2+1 from dual connect by level <= 1000000;
commit;
create index my_table_index on my_table(start_num, end_num);
begin
    dbms_stats.gather_table_stats(user, 'MY_TABLE', no_invalidate => false);
end;
/

低数字几乎是瞬时的 - 0.015 秒

select start_num from my_table where 2 between start_num and end_num;

数字越大越慢 - 0.125 秒

select start_num from my_table where 1000000 between start_num and end_num;

范围扫描和全表扫描之间只有一个点。

explain plan for select start_num from my_table where 402741 between start_num and end_num;
select * from table(dbms_xplan.display);

Plan hash value: 3804444429

------------------------------------------------------------------------------
| Id  | Operation         | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |          |   160K|  1570K|   622   (2)| 00:00:08 |
|*  1 |  TABLE ACCESS FULL| MY_TABLE |   160K|  1570K|   622   (2)| 00:00:08 |
------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("START_NUM"<=402742 AND "END_NUM">=402742)


explain plan for select start_num from my_table where 402742 between start_num and end_num;
select * from table(dbms_xplan.display);


Plan hash value: 3804444429

------------------------------------------------------------------------------
| Id  | Operation         | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |          |   160K|  1570K|   622   (2)| 00:00:08 |
|*  1 |  TABLE ACCESS FULL| MY_TABLE |   160K|  1570K|   622   (2)| 00:00:08 |
------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("START_NUM"<=402742 AND "END_NUM">=402742)

但问题不在于 Oracle 不使用索引。以幼稚的方式使用索引并没有帮助。事实上，这甚至更慢，为 0.172 秒：

select /*+ index(my_table my_table_index) */ start_num
from my_table
where 1000000 between start_num and end_num;

解决方案

创建新索引：

drop index my_table_index;
create index my_table_index1 on my_table(start_num);
create index my_table_index2 on my_table(end_num);
begin
    dbms_stats.gather_table_stats(user, 'MY_TABLE', no_invalidate => false);
end;
/

对于任何数字，结果都是即时的：

select start_num
from my_table
where
    start_num =
    (
        --Last start <= number
        select start_num
        from
        (
            select start_num
            from my_table
            where 1000000 >= start_num
            order by start_num desc
        )
        where rownum = 1
    ) and
    end_num =
    (
        --First end >= number
        select end_num
        from
        (
            select end_num
            from my_table
            where 1000000 <= end_num
            order by end_num
        )
        where rownum = 1
    );

该计划看起来很棒 - 这可能是您可以获得的最佳性能。

Plan hash value: 522166032

--------------------------------------------------------------------------------------------------
| Id  | Operation                      | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT               |                 |     1 |    10 |    10   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS BY INDEX ROWID   | MY_TABLE        |     1 |    10 |     4   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN             | MY_TABLE_INDEX2 |     1 |       |     3   (0)| 00:00:01 |
|*  3 |    COUNT STOPKEY               |                 |       |       |            |          |
|   4 |     VIEW                       |                 |     3 |    39 |     3   (0)| 00:00:01 |
|*  5 |      INDEX RANGE SCAN          | MY_TABLE_INDEX2 |     3 |    18 |     3   (0)| 00:00:01 |
|*  6 |   COUNT STOPKEY                |                 |       |       |            |          |
|   7 |    VIEW                        |                 |     2 |    26 |     3   (0)| 00:00:01 |
|*  8 |     INDEX RANGE SCAN DESCENDING| MY_TABLE_INDEX1 |   500K|  2929K|     3   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("START_NUM"= (SELECT "START_NUM" FROM  (SELECT "START_NUM" "START_NUM" FROM 
              "MY_TABLE" "MY_TABLE" WHERE "START_NUM"<=1000000 ORDER BY "START_NUM" DESC) 
              "from$_subquery$_002" WHERE ROWNUM=1))
   2 - access("END_NUM"= (SELECT "END_NUM" FROM  (SELECT "END_NUM" "END_NUM" FROM 
              "MY_TABLE" "MY_TABLE" WHERE "END_NUM">=1000000 ORDER BY "END_NUM") "from$_subquery$_004" 
              WHERE ROWNUM=1))
   3 - filter(ROWNUM=1)
   5 - access("END_NUM">=1000000)
   6 - filter(ROWNUM=1)
   8 - access("START_NUM"<=1000000)
于 2013-04-06T04:58:48.950 回答
0

这是一个试图欺骗甲骨文使其表现得像其竞争对手一样的案例，而我只是猜测无法访问甲骨文。也许自我加入可以做到这一点？分别在每列上使用索引，

SELECT t1.start
FROM my_table t1 JOIN my_table t2
ON t1.start=t2.start AND t2."end"=t1."end"
AND t1.start <= :1
AND t2.end >= :1

这看起来很傻，但直接的解决方案是 Joe Frambach 的。它愚弄了我确实拥有的 Postgres，只进行索引搜索。

end顺便说一句，Postgres 对作为列名非常不满意。我希望你的真实表不在那里使用保留字。

于 2013-04-05T05:15:02.887 回答
0

我认为您应该创建 2 个索引，一个在开始列上，一个在结束列上。然后不要选择 between 选项，而是选择大于然后开始和小于然后结束的位置。然后，您将为每个 where 子句使用一个索引。

我希望这有助于提高性能。

于 2013-04-04T19:31:55.940 回答