月归档：二月 2011

oracle 中如何定位重要(消耗资源多)的SQL

发表于 2011 年 2 月 17 日 由 惜分飞

1、查看值得怀疑的SQL

select substr(to_char(s.pct,'99.00'),2)||'%'load,
       s.executions executes,
       p.sql_text
from(select address,
               disk_reads,
               executions,
               pct,
               rank()over(order by disk_reads desc) ranking
         from(select address,
                       disk_reads,
                       executions,
                      100*ratio_to_report(disk_reads)over() pct
                 from sys.v_$sql
                where command_type!=47)
        where disk_reads>50*executions) s,
       sys.v_$sqltext p
where s.ranking<=5
  and p.address=s.address
order by 1, s.address, p.piece;

2、查看消耗内存多的sql

select b.username,
       a. buffer_gets,
       a.executions,
       a.disk_reads / decode(a.executions, 0, 1, a.executions),
       a.sql_text SQL
  from v$sqlarea a, dba_users b
 where a.parsing_user_id = b.user_id
   and a.disk_reads > 10000
 order by disk_reads desc;

3、查看逻辑读多的SQL

select*
from(select buffer_gets, sql_text
         from v$sqlarea
        where buffer_gets>500000
        order by buffer_gets desc)
where rownum<=30;

4、查看执行次数多的SQL

select sql_text, executions
  from (select sql_text, executions from v$sqlarea order by executions desc)
 where rownum < 81;

5、查看读硬盘多的SQL

select sql_text, disk_reads
from(select sql_text, disk_reads from v$sqlarea order by disk_reads desc)
where rownum<21;

6、查看排序多的SQL

select sql_text, sorts
from(select sql_text, sorts from v$sqlarea order by sorts desc)
where rownum<21;

7、分析的次数太多，执行的次数太少，要用绑变量的方法来写sql

select substr(sql_text, 1, 80) "sql", count(*), sum(executions) "totexecs"
  from v$sqlarea
 where executions < 5
 group by substr(sql_text, 1, 80)
having count(*) > 30
 order by 2;
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全角，半角互换

发表于 2011 年 2 月 17 日 由 惜分飞

对于全角和半角互换，oracle 提供了两个函数to_multi_byte和to_single_byte函数

 select to_multi_byte('1234') from dual;
 
TO_MULTI_BYTE('1234')
---------------------
１２３４
 select to_single_byte('１２３４') from dual;
 
TO_SINGLE_BYTE('１２３４')
--------------------------
1234
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在sqlplus中操作blob和clob

发表于 2011 年 2 月 16 日 由 惜分飞 
--create directory 
create directory ULTLOBDIR as 'd:'

--create table
create table blobtest(col1 BLOB);
create table clobtest(col1 cLOB);

--insert BLOB
declare
a_blob BLOB;
bfile_name BFILE := BFILENAME('ULTLOBDIR','teslob.doc');
begin
insert into blobtest values (empty_blob())
returning col1 into a_blob;
dbms_lob.fileopen(bfile_name);
dbms_lob.loadfromfile(a_blob, bfile_name, dbms_lob.getlength(bfile_name));
dbms_lob.fileclose(bfile_name);
commit;
end;

--update BLOB
declare
a_blob BLOB;
bfile_name BFILE := BFILENAME('ULTLOBDIR','log.txt');
begin
update blobtest set col1=empty_blob() where rownum=1
returning col1 into a_blob;
dbms_lob.fileopen(bfile_name);
dbms_lob.loadfromfile(a_blob, bfile_name, dbms_lob.getlength(bfile_name));
dbms_lob.fileclose(bfile_name);
commit;
end;

--insert CLOB
declare
a_clob CLOB;
bfile_name BFILE := BFILENAME('ULTLOBDIR','teslob.doc');
begin
insert into clobtest values (empty_clob())
returning col1 into a_clob;
dbms_lob.fileopen(bfile_name);
dbms_lob.loadfromfile(a_clob, bfile_name, dbms_lob.getlength(bfile_name));
dbms_lob.fileclose(bfile_name);
commit;
end;

--update CLOB
declare
a_clob CLOB;
bfile_name BFILE := BFILENAME('ULTLOBDIR','log.txt');
begin
update clobtest set col1=empty_clob() where rownum=1
returning col1 into a_clob;
dbms_lob.fileopen(bfile_name);
dbms_lob.loadfromfile(a_clob, bfile_name, dbms_lob.getlength(bfile_name));
dbms_lob.fileclose(bfile_name);
commit;
end;

--查询是否成功
select dbms_lob.getlength(col1) from blobtest;
select dbms_lob.getlength(col1) from clobtest;
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