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Oracle的control文件
這里我們要實(shí)驗(yàn)的是數(shù)據(jù)庫在open的狀態(tài)下,破快控制文件,數(shù)據(jù)庫會不會down
查看controlfiles的路徑
SQL> show parameter control_files
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
control_files string /u01/app/oracle/oradata/orcl/control01.ctl, /u01/app/oracle/fast_recovery_area/orcl/control02.ctl
破壞控制文件
[oracle@togogo ~]$ cat /dev/null > /u01/app/oracle/oradata/orcl/control01.ctl
[oracle@togogo ~]$ cat /dev/null > /u01/app/oracle/fast_recovery_area/orcl/control02.ctl
驗(yàn)證數(shù)據(jù)庫的狀態(tài)
SQL> select * from dual;
D
-
X
#### 做檢查點(diǎn),切換redo log
SQL> alter system checkpoint;
System altered.
SQL> alter system switch logfile;
System altered.
SQL> alter system switch logfile;
System altered.
#### check alert log
Sat Feb 10 20:09:55 2018
Thread 1 cannot allocate new log, sequence 8
Private strand flush not complete
Current log# 1 seq# 7 mem# 0: /u01/app/oracle/oradata/orcl/redo01.log
Thread 1 advanced to log sequence 8 (LGWR switch)
Current log# 2 seq# 8 mem# 0: /u01/app/oracle/oradata/orcl/redo02.log
Sat Feb 10 20:10:19 2018
Thread 1 cannot allocate new log, sequence 9
Private strand flush not complete
Current log# 2 seq# 8 mem# 0: /u01/app/oracle/oradata/orcl/redo02.log
Thread 1 advanced to log sequence 9 (LGWR switch)
Current log# 3 seq# 9 mem# 0: /u01/app/oracle/oradata/orcl/redo03.log
Thread 1 cannot allocate new log, sequence 10
Checkpoint not complete
Current log# 3 seq# 9 mem# 0: /u01/app/oracle/oradata/orcl/redo03.log
Thread 1 cannot allocate new log, sequence 10
Private strand flush not complete
Current log# 3 seq# 9 mem# 0: /u01/app/oracle/oradata/orcl/redo03.log
Thread 1 advanced to log sequence 10 (LGWR switch)
Current log# 1 seq# 10 mem# 0: /u01/app/oracle/oradata/orcl/redo01.log
這是為什么呢?那是因?yàn)槠溥M(jìn)程持有的句柄并有釋放,如下
[oracle@togogo ~]$ ps -ef|grep ckpt|grep -v grep
oracle 8427 1 0 19:47 ? 00:00:00 ora_ckpt_orcl
[oracle@togogo ~]$ cd /proc/8427/fd
[oracle@togogo fd]$ ls -ltr |grep control
lrwx------ 1 oracle oinstall 64 Feb 10 20:09 257 -> /u01/app/oracle/fast_recovery_area/orcl/control02.ctl
lrwx------ 1 oracle oinstall 64 Feb 10 20:09 256 -> /u01/app/oracle/oradata/orcl/control01.ctl
#### session 1 trace跟蹤
這里說一個命令 strace
舉一個例子
strace -o output.txt -T -tt -e trace=all -p 28979
上面的含義是 跟蹤28979進(jìn)程的所有系統(tǒng)調(diào)用(-e trace=all),并統(tǒng)計(jì)系統(tǒng)調(diào)用的花費(fèi)時(shí)間,以及開始時(shí)間(并以可視化的時(shí)分秒格式顯示),最后將記錄結(jié)果存在output.txt文件里面
[oracle@togogo fd]$ strace -fr -o /tmp/8427.log -p 8427
Process 8427 attached - interrupt to quit
####觀察trace.log
8427 0.000156 gettimeofday({1518265363, 443228}, NULL) = 0
8427 0.000176 gettimeofday({1518265543, 106769}, NULL) = 0
8427 0.000077 gettimeofday({1518265543, 106845}, NULL) = 0
8427 0.000072 gettimeofday({1518265543, 106917}, NULL) = 0
8427 0.000077 pwrite64(256, "\25\302\0\0\3\0\0\0\0\0\0\0\0\0\1\4\312T\0\0\2\0\0\0\0\0\0\0Q\0\0\0"..., 16384, 49152) = 16384
8427 0.006462 gettimeofday({1518265543, 113463}, NULL) = 0
8427 0.000089 gettimeofday({1518265543, 113548}, NULL) = 0
8427 0.000080 pwrite64(257, "\25\302\0\0\3\0\0\0\0\0\0\0\0\0\1\4\312T\0\0\2\0\0\0\0\0\0\0Q\0\0\0"..., 16384, 49152) = 16384
8427 0.000734 gettimeofday({1518265543, 114364}, NULL) = 0
8427 0.000081 gettimeofday({1518265543, 114443}, NULL) = 0
8427 0.000081 gettimeofday({1518265543, 114525}, NULL) = 0
8427 0.000078 gettimeofday({1518265543, 114603}, NULL) = 0
8427 0.000211 gettimeofday({1518265543, 114816}, NULL) = 0
8427 0.000080 gettimeofday({1518265543, 114891}, NULL) = 0
8427 0.000081 pread64(256, "\25\302\0\0\1\0\0\0\0\0\0\0\0\0\1\4r\t\0\0\0\0\0\0\0\0 \v\373M\21Y"..., 16384, 16384) = 16384
這的 256 257 是表示的是文件描述符 FD file discription
16384是表示一個塊的大小
49152是表示偏移量
通過以上可以得到結(jié)論
1. 進(jìn)程信息可以在/proc下看到,例如: /proc/8427/stat
2. 對于linux,對于文件的讀寫,是通過調(diào)用函數(shù)read,pwrite64 來實(shí)現(xiàn)的。
3. 我們可以發(fā)現(xiàn)檢查點(diǎn)進(jìn)程ckpt 3s觸發(fā)一次的機(jī)制。
4. 對于pwrite64的操作,是通過寫fd (256.257)2個文件來完成的,其中對應(yīng)的offset都是49152,且我們知道這3個被寫入的文件 (我們知道是controlfile) 的block大小是16384.
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