数据库平台：SunOS 5.8 Generic_108528-23 sun4u sparc SUNW,Ultra-Enterprise数据库版本：8.1.5.0.0数据库症状：数据库响应缓慢，应用请求无法返回，业务操作陷于停顿，此时需要DBA介入并进行问题诊断及故障处理。 1. 登录数据库进行检查
首先我们登录数据库,检查故障现象。
经过检查发现，数据块的所有重做日志组除current外都处于active状态：
oracle:/oracle/oracle8sqlplus "/ as sysdba"
SQL*Plus: Release 8.1.5.0.0 - Production on Thu Jun 23 18:56:06 2005
(c) Copyright 1999 Oracle Corporation. All rights reserved.
Connected to:
Oracle8i Enterprise Edition Release 8.1.5.0.0 - Production
With the Partitioning and Java options
PL/SQL Release 8.1.5.0.0 - Production
SQL select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM
---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- ---------
1 1 520403 31457280 1 NO ACTIVE 1.3861E+10 23-JUN-05
2 1 520404 31457280 1 NO ACTIVE 1.3861E+10 23-JUN-05
3 1 520405 31457280 1 NO ACTIVE 1.3861E+10 23-JUN-05
4 1 520406 31457280 1 NO CURRENT 1.3861E+10 23-JUN-05
5 1 520398 31457280 1 NO ACTIVE 1.3860E+10 23-JUN-05
6 1 520399 31457280 1 NO ACTIVE 1.3860E+10 23-JUN-05
7 1 520400 104857600 1 NO ACTIVE 1.3860E+10 23-JUN-05
8 1 520401 104857600 1 NO ACTIVE 1.3860E+10 23-JUN-05
9 1 520402 104857600 1 NO ACTIVE 1.3861E+10 23-JUN-05
9 rows selected.
SQL /
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM
---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- ---------
1 1 520403 31457280 1 NO ACTIVE 1.3861E+10 23-JUN-05
2 1 520404 31457280 1 NO ACTIVE 1.3861E+10 23-JUN-05
3 1 520405 31457280 1 NO ACTIVE 1.3861E+10 23-JUN-05
4 1 520406 31457280 1 NO CURRENT 1.3861E+10 23-JUN-05
5 1 520398 31457280 1 NO ACTIVE 1.3860E+10 23-JUN-05
6 1 520399 31457280 1 NO ACTIVE 1.3860E+10 23-JUN-05
7 1 520400 104857600 1 NO ACTIVE 1.3860E+10 23-JUN-05
8 1 520401 104857600 1 NO ACTIVE 1.3860E+10 23-JUN-05
9 1 520402 104857600 1 NO ACTIVE 1.3861E+10 23-JUN-05
9 rows selected.
我们知道，当数据库发生日志切换时（Log Switch）,Oracle会触发一个检查点（Checkpoint），检查点进程（Checkpoint Process，CKPT）会通知DBWR（Database?Writer）进程去执行写操作。在日志文件所保护的处于Buffer cache中的脏数据（dirty buffer）未写回磁盘之前，日志文件不能被覆盖或重用。
如果数据库异常繁忙，或者DBWR的写出过慢，就可能出现检查点未完成，Oracle却已经用完所有日志文件的情况。在这种情况下，数据库的日志无法生成，整个数据库将处于停顿状态，此时日志文件中会记录类似如下信息：
bordercolorlight = "black" bordercolordark = "#FFFFFF" align="center"
Mon Jan 23 16:11:39 2006Thread 1 cannot allocate new log,
sequence 5871Checkpoint not complete Current log# 2 seq# 5870 mem# 0:
+ORADG/danaly/onlinelog/group_2.260.600173851
Current log# 2 seq# 5870 mem# 1:
+ORADG/danaly/onlinelog/group_2.261.600173853
检查v$session_wait视图，我们可以从中看到很多session处于log file switch (checkpoint incomplete) 的等待。
2. 检查DBWR进程
在本案例中，所有日志组都处于active状态，那么显然DBWR的写出存在问题。
接下来让我们检查一下DBWR的繁忙程度:
SQL !
oracle:/oracle/oracle8ps -ef|grep ora_
oracle 2273 1 0 Mar 31 ? 57:40 ora_smon_hysms02
oracle 2266 1 0 Mar 31 ? 811:42 ora_dbw0_hysms02
oracle 2264 1 16 Mar 31 ? 16999:57 ora_pmon_hysms02
oracle 2268 1 0 Mar 31 ? 1649:07 ora_lgwr_hysms02
oracle 2279 1 0 Mar 31 ? 8:09 ora_snp1_hysms02
oracle 2281 1 0 Mar 31 ? 4:22 ora_snp2_hysms02
oracle 2285 1 0 Mar 31 ? 9:40 ora_snp4_hysms02
oracle 2271 1 0 Mar 31 ? 15:57 ora_ckpt_hysms02
oracle 2283 1 0 Mar 31 ? 5:37 ora_snp3_hysms02
oracle 2277 1 0 Mar 31 ? 5:58 ora_snp0_hysms02
oracle 2289 1 0 Mar 31 ? 0:00 ora_d000_hysms02
oracle 2287 1 0 Mar 31 ? 0:00 ora_s000_hysms02
oracle 2275 1 0 Mar 31 ? 0:04 ora_reco_hysms02
oracle 21023 21012 0 18:52:59 pts/65 0:00 grep ora_
DBWR的进程号是2266。
使用Top命令观察一下该进程的CPU耗用:
oracle:/oracle/oracle8top
last pid: 21145; load averages: 3.38, 3.45, 3.67 18:53:38
725 processes: 711 sleeping, 1 running, 10 zombie, 3 on cpu
CPU states: 35.2% idle, 40.1% user, 9.4% kernel, 15.4% iowait, 0.0% swap
Memory: 3072M real, 286M free, 3120M swap in use, 1146M swap free
PID USERNAME THR PRI NICE SIZE RES STATE TIME CPU COMMAND
11855 smspf 1 59 0 1355M 1321M cpu/0 19:32 16.52% oracle
2264 oracle 1 0 0 1358M 1316M run 283.3H 16.36% oracle
11280 oracle 1 13 0 1356M 1321M sleep 79.8H 0.77% oracle
6957 smspf 15 29 10 63M 14M sleep 107.7H 0.76% java
17393 smspf 1 30 0 1356M 1322M cpu/1 833:05 0.58% oracle
29299 smspf 5 58 0 8688K 5088K sleep 18.5H 0.38% fee_ftp_get
21043 oracle 1 43 0 3264K 2056K cpu/9 0:01 0.31% top
20919 smspf 17 29 10 63M 17M sleep 247:02 0.29% java
25124 smspf 1 58 0 16M 4688K sleep 0:35 0.25% smif_status_rec
8086 smspf 5 23 0 21M 13M sleep 41.1H 0.24% fee_file_in
16009 root 1 35 0 4920K 3160K sleep 0:03 0.21% sshd2
25126 smspf 1 58 0 1355M 1321M sleep 0:26 0.20% oracle
2266 oracle 1 60 0 1357M 1317M sleep 811:42 0.18% oracle
11628 smspf 7 59 0 3440K 2088K sleep 0:39 0.16% sgip_client_ltz
26257 smspf 82 59 0 447M 178M sleep 533:04 0.15% java
我们注意到，2266号进程消耗的CPU不过0.18%,显然并不繁忙,DBWR并不繁忙，但是检查点无法完成，那么我们可以判断，瓶颈就很可能出现在IO上。
3. 检查IO状况
我们可以使用IOSTAT工具检查系统IO状况：
gqgai:/home/gqgaiiostat -xn 3
extended device statistics
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
......
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 c0t6d0
1.8 38.4 32.4 281.0 0.0 0.7 0.0 16.4 0 29 c0t10d0
1.8 38.4 32.4 281.0 0.0 0.5 0.0 13.5 0 27 c0t11d0
24.8 61.3 1432.4 880.1 0.0 0.5 0.0 5.4 0 26 c1t1d0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 9.1 0 0 hurraysms02:vold(pid238)
extended device statistics
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
........
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 c0t6d0
0.3 8.3 0.3 47.0 0.0 0.1 0.0 9.2 0 8 c0t10d0
0.0 8.3 0.0 47.0 0.0 0.1 0.0 8.0 0 7 c0t11d0
11.7 65.3 197.2 522.2 0.0 1.6 0.0 20.5 0 100 c1t1d0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 hurraysms02:vold(pid238)
extended device statistics
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
........
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 c0t6d0
0.3 13.7 2.7 68.2 0.0 0.2 0.0 10.9 0 12 c0t10d0
0.0 13.7 0.0 68.2 0.0 0.1 0.0 9.6 0 11 c0t11d0
11.3 65.3 90.7 522.7 0.0 1.5 0.0 19.5 0 99 c1t1d0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 hurraysms02:vold(pid238)
extended device statistics
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
........
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 c0t6d0
0.0 8.0 0.0 42.7 0.0 0.1 0.0 9.3 0 7 c0t10d0
0.0 8.0 0.0 42.7 0.0 0.1 0.0 9.1 0 7 c0t11d0
11.0 65.7 978.7 525.3 0.0 1.4 0.0 17.7 0 99 c1t1d0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 hurraysms02:vold(pid238)
extended device statistics
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
........
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 c0t6d0
0.3 87.7 2.7 433.7 0.0 2.2 0.0 24.9 0 90 c0t10d0
0.0 88.3 0.0 436.5 0.0 1.8 0.0 19.9 0 81 c0t11d0
89.0 54.0 725.4 432.0 0.0 2.1 0.0 14.8 0 100 c1t1d0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 hurraysms02:vold(pid238)
在以上输出中，我们注意到，存放数据库的主要卷c1t1d0的繁忙程度始终处于99~100,而写速度却只有500K/s左右，这个速度是极为缓慢的。
根据IOSTAT的手册:
(%b percent of time the disk is busy (transactions in progress)
Kw/s kilobytes written per second)
根据我们的常识，T3盘阵通常按Char写速度可以达到10M/s左右，以前测试过一些Tpcc指标，可以参考：www.eygle.com/unix/Use.Bonnie.To.Test.IO.speed.htm。
而正常情况下的数据库随机写通常都在1~2M左右，显然此时的磁盘已经处于不正常状态，经过确认的确是硬盘发生了损坏，Raid5的Group中损坏了一块硬盘。
经过更换以后系统逐渐恢复正常。
(e129)
