一个是oracle数据库1毫秒可执行多少次内存hash运算操作，这个主要用于量化hash join的时间;
一个是oracle数据库1毫秒可执行多少次内存排序的比较运算，这个主要用于量化order by的时间。
以下是测试结果，让我非常意外。
以下是测试代码，测试采用单会话sqlplus执行，因此只能衡量主机CPU单核的性能。
下面这个是hash次数的测试代码：
declare i integer; int1 integer; t1 number; t2 number; t_all number; t_select number; execute_count number := 10; function getnumfromtimestamp(iTime timestamp) return number is Result number; v_hour number; v_minute number; v_second number; v_millisecond number; begin v_hour := EXTRACT(hour from iTime); v_minute := EXTRACT(minute from iTime); v_second := EXTRACT(second from iTime); Result := (v_hour + 1) * 3600 + (v_minute + 1) * 60 + v_second; return(Result); end; begin select /*+use_hash(a,b)*/ count(*) into int1 from (select rownum + 20000000 rn from dual connect by rownum <= 1000000) a, (select rownum + 10000000 rn from dual connect by rownum <= 1000000) b where a.rn = b.rn; t1 := getnumfromtimestamp(systimestamp); for i in 1 .. execute_count loop select /*+use_hash(a,b)*/ count(*) into int1 from (select rownum + 20000000 rn from dual connect by rownum <= 1000000) a, (select rownum + 10000000 rn from dual connect by rownum <= 1000000) b where a.rn = b.rn; end loop; t2 := getnumfromtimestamp(systimestamp); t_all := t2 - t1; select count(*) into int1 from (select rownum + 20000000 rn from dual connect by rownum <= 1000000); t1 := getnumfromtimestamp(systimestamp); for i in 1 .. execute_count loop select count(*) into int1 from (select rownum + 20000000 rn from dual connect by rownum <= 1000000); end loop; t2 := getnumfromtimestamp(systimestamp); t_select := t2 - t1; dbms_output.put_line('hash_times:' || trunc(1000 / ((t_all - t_select) / (2 * execute_count)))); end; / |
