oracle数据库常见故障处理

 一、定位数据库故障原因。
定位原因大概可以分三步走：
1、如果有oracle错误号或者alert日志中有详细的出错信息，则可以根据这些去定位数据库故障原因；
2、如果没有，则可以运行awr工具或者statspack工具生成报告，根据报告去定位数据库故障原因；
3、如果没有上述工具，则可以查看相关数据库字典，去定位数据库故障原因。
 
脚本1：下面语句用v$sysstat视图检索数据库开销和cpu等待时间，从而是判断你的数据库是否发生了资源等待事件。
select
 round(100*CPU_sec/available_time,2) "ORACLE CPU TIME AS % AVAIL."
,round(100*(DB_sec - CPU_sec)/available_time,2) "NON-IDLE WAITS AS % AVAIL."
,case
  sign(available_time - DB_sec)
  when 1 then round(100*(available_time - DB_sec) / available_time, 2)
  else 0
  end "ORACLE IDLE AS % AVAIL."
from
(
  select
    (sysdate - i.startup_time) * 86400 * c.cpus available_time
   ,t.DB_sec
   ,t.CPU_sec
  from v$instance i
 ,(select value cpus
   from v$parameter
   where name = 'cpu_count') c
 ,(select
    sum(case name
         when 'DB time' then round(value/100)
         else 0
         end) DB_sec
   ,sum(case name
         when 'DB time' then 0
         else round(value/100)
         end) CPU_sec
   from v$sysstat
   where name in ('DB time', 'CPU used by this session')) t
where i.instance_number = userenv('INSTANCE')
);
 
Here is some output:
ORACLE CPU TIME AS % AVAIL. NON-IDLE WAITS AS % AVAIL. ORACLE IDLE AS % AVAIL.
--------------------------- -------------------------- -----------------------
                                31.97                         129.59         
脚本2：上面的查询结果（NON-IDLE WAITS）显示数据库存在大量等待事件，下面的语句可以查出具体的等待事件。
col wait_class format A15
col event format A35 trunc
col "CLASS AS % OF WHOLE" format 990.00 HEAD "CLASS AS|% OF WHOLE"
col "EVENT AS % OF CLASS" like "CLASS AS % OF WHOLE" HEAD "EVENT AS|% OF CLASS"
col "EVENT AS % OF WHOLE" like "CLASS AS % OF WHOLE" HEAD "EVENT AS|% OF WHOLE"
set pagesize 30
break on wait_class on "CLASS AS % OF WHOLE"
--
select
  wait_class,
  round(100 * time_class / total_waits, 2) "CLASS AS % OF WHOLE",
  event,
  round(100 * time_waited / time_class, 2) "EVENT AS % OF CLASS",
  round(100 * time_waited / total_waits, 2) "EVENT AS % OF WHOLE"
from
(select
  wait_class
 ,event
 ,time_waited
 ,sum(time_waited) over (partition by wait_class) time_class
 ,rank() over (partition by wait_class order by time_waited desc) rank_within_class
 ,sum(time_waited) over () total_waits
from v$system_event
where wait_class <> 'Idle')
where rank_within_class <= 3
order by time_class desc, rank_within_class;
 
三、判断在线重做日志大小是否合适。
问题：如果发生log file switch (checkpoint incomplete) 等待事件，需要检测在线重做日志交换的频率。
脚本1：这个脚本可以查看每小时在线日志交换的次数，一般的做法，如果日志交换次数过频繁，可以适当调整一下在线日志的大小。
select count(*), to_char(first_time, 'YYYY:MM:DD:HH24')
  from v$log_history
 group by to_char(first_time, 'YYYY:MM:DD:HH24')
 order by 2;
脚本2：查看相关在线重做日志文件。
select a.group#, a.member, b.status, b.bytes / 1024 / 1024 meg_bytes
  from v$logfile a, v$log b
 where a.group# = b.group#
 order by a.group#;
 
四、判断undo表空间大小是否合适。
问题：运行长sql语句的时候，发生ORA-01555 “snapshot too old” 错误，需要检查一下undo表空间大小是否合适。
脚本：
select
 to_char(begin_time,'MM-DD-YYYY HH24:MI') begin_time
,ssolderrcnt       ORA_01555_cnt
,nospaceerrcnt     no_space_cnt
,txncount          max_num_txns
,maxquerylen       max_query_len
,expiredblks       blck_in_expired
from v$undostat
where begin_time > sysdate - 1
order by begin_time;
注：
1、ORA_01555_cnt列表明是否发生了ORA-01555错误，如果发生，则判断下面几步：
*Ensure that code does not contain COMMIT statements within cursor loops.
*Tune the SQL statement throwing the error so that it runs faster.
*Ensure that you have good statistics (so your SQL runs efficiently).
*Increase the UNDO_RETENTION initialization parameter.
2、如果NO_SPACE_CNT列非0，需要增大undo表空间大小。
3、现在undo表空间的大小和oracle建议大小。
 select sum(bytes) / 1024 / 1024 cur_mb_size,
       dbms_undo_adv.required_undo_size(900) req_mb_size
  from dba_data_files
 where tablespace_name LIKE 'UNDO%';
 
五、判断临时表空间大小是否合适。
问题：ORA-01652: unable to extend temp segment by 128 in tablespace TEMP
select tablespace_name, sum(bytes_used) / 1024 / 1024 mb_used
  from v$temp_extent_pool
 group by tablespace_name;
select name, bytes/1024/1024 mb_alloc from v$tempfile;
alter database tempfile '/ora03/DWREP/temp03.dbf' resize 12g;  或者
alter tablespace temp add tempfile '/ora04/DWREP/temp04.dbf' size 2g;
 
六、检查表空间使用情况。
select a.tablespace_name,
       (f.bytes / a.bytes) * 100 pct_free,
       f.bytes / 1024 / 1024 mb_free,
       a.bytes / 1024 / 1024 mb_allocated
  from (select nvl(sum(bytes), 0) bytes, x.tablespace_name
          from dba_free_space y, dba_tablespaces x
         where x.tablespace_name = y.tablespace_name(+)
           and x.contents != 'TEMPORARY'
           and x.status != 'READ ONLY'
           and x.tablespace_name not like 'UNDO%'
         group by x.tablespace_name) f,
       (select sum(bytes) bytes, tablespace_name
          from dba_data_files
         group by tablespace_name) a
 where a.tablespace_name = f.tablespace_name
 order by 1;
 
REM *****************************************************
REM * File : freesp.sql
REM *****************************************************
SET PAGESIZE 100 LINES 132 ECHO OFF VERIFY OFF FEEDB OFF SPACE 1 TRIMSP ON
COMPUTE SUM OF a_byt t_byt f_byt ON REPORT
BREAK ON REPORT ON tablespace_name ON pf
COL tablespace_name FOR A17        TRU HEAD 'Tablespace|Name'
COL file_name          FOR A40     TRU HEAD 'Filename'
COL a_byt              FOR 9,990.999 HEAD 'Allocated|GB'
COL t_byt              FOR 9,990.999 HEAD 'Current|Used GB'
COL f_byt              FOR 9,990.999 HEAD 'Current|Free GB'
COL pct_free           FOR 990.0        HEAD 'File %|Free'
COL pf                 FOR 990.0        HEAD 'Tbsp %|Free'
COL seq NOPRINT
DEFINE b_div=1073741824
--
COL db_name NEW_VALUE h_db_name NOPRINT
COL db_date NEW_VALUE h_db_date NOPRINT
SELECT name db_name, TO_CHAR(sysdate,'YYYY_MM_DD') db_date FROM v$database;
--
SPO &&h_db_name._&&h_db_date..lis
PROMPT Database: &&h_db_name, Date: &&h_db_date
      --
SELECT 1 seq,
       b.tablespace_name,
       nvl(x.fs, 0) / y.ap * 100 pf,
       b.file_name file_name,
       b.bytes / &&b_div a_byt,
       NVL((b.bytes - SUM(f.bytes)) / &&b_div, b.bytes / &&b_div) t_byt,
       NVL(SUM(f.bytes) / &&b_div, 0) f_byt,
       NVL(SUM(f.bytes) / b.bytes * 100, 0) pct_free
  FROM dba_free_space f,
       dba_data_files b,
       (SELECT y.tablespace_name, SUM(y.bytes) fs
          FROM dba_free_space y
         GROUP BY y.tablespace_name) x,
       (SELECT x.tablespace_name, SUM(x.bytes) ap
          FROM dba_data_files x
         GROUP BY x.tablespace_name) y
 WHERE f.file_id(+) = b.file_id
   AND x.tablespace_name(+) = y.tablespace_name
   and y.tablespace_name = b.tablespace_name
   AND f.tablespace_name(+) = b.tablespace_name
 GROUP BY b.tablespace_name,
          nvl(x.fs, 0) / y.ap * 100,
          b.file_name,
          b.bytes
UNION
SELECT 2 seq,
       tablespace_name,
       j.bf / k.bb * 100 pf,
       b.name file_name,
       b.bytes / &&b_div a_byt,
       a.bytes_used / &&b_div t_byt,
       a.bytes_free / &&b_div f_byt,
       a.bytes_free / b.bytes * 100 pct_free
  FROM v$temp_space_header a,
       v$tempfile b,
       (SELECT SUM(bytes_free) bf FROM v$temp_space_header) j,
       (SELECT SUM(bytes) bb FROM v$tempfile) k
 WHERE a.file_id = b.file#
 ORDER BY 1, 2, 4, 3;
--
COLUMN name FORMAT A60 HEAD 'Control Files'
SELECT name FROM v$controlfile;
--
COL member       FORMAT A50 HEAD 'Redo log files'
COL status       FORMAT A9    HEAD 'Status'
COL archived     FORMAT A10 HEAD 'Archived'
--
SELECT
  a.group#, a.member, b.status,
  b.archived, SUM(b.bytes)/1024/1024 mb
FROM v$logfile a, v$log b
WHERE a.group# = b.group#
GROUP BY a.group#, a.member, b.status, b.archived
ORDER BY 1, 2;
--
七、检查索引使用情况。
1、alter index F_DOWN_DOM_FK9 monitoring usage;
2、select * from v$object_usage;
3、select 'alter index ' || index_name || ' monitoring usage;' from user_indexes;