复习之前的学习内容，对public redo thread 和 private redo thread 的用处还是比较模糊，网上搜集的资料非常有限，看来有些好东西不跳墙是不行的。
废话少说，知识点记录下来：
在rac环境下，每个实例都有自己的redo log，这套redo log称为redo thread。这套概念同样适用於单实例数据库。
redo thread有两种，private 和 public ，在默认情况下，我们使用的是public thread。但是如果我们在创建redol log时明确指定了thread参数，那么该redo为private redo。
实验如下：
单实例：
SQL> l
1* select thread#,status,enabled from v$thread
SQL> /
THREAD# STATUS ENABLED
---------- ------ --------
1 OPEN PUBLIC
SQL> select group#,thread#,status from v$log;
GROUP# THREAD# STATUS
---------- ---------- ----------------
4 1 INACTIVE
5 1 CURRENT
SQL> col member for a60
SQL> select group#,member from v$logfile;
GROUP# MEMBER
---------- ------------------------------------------------------------
4 /home/app/oraten/oradata/oraten/redo04.log
5 /home/app/oraten/oradata/oraten/redo05.log
SQL> alter database add logfile thread 2 group 6 '/home/app/oraten/oradata/oraten/redo06.log' size 100M;
Database altered.
SQL> alter database add logfile thread 2 group 7 '/home/app/oraten/oradata/oraten/redo07.log' size 100M;
Database altered.
SQL> select thread#,status,enabled from v$thread;
THREAD# STATUS ENABLED
---------- ------ --------
1 OPEN PUBLIC
2 CLOSED DISABLED
SQL> alter database enable thread 2;
Database altered.
SQL> select thread#,status,enabled from v$thread;
THREAD# STATUS ENABLED
---------- ------ --------
1 OPEN PUBLIC
2 CLOSED PRIVATE
SQL> show parameter thread
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
parallel_threads_per_cpu integer 2
thread integer 1
SQL> alter system set thread=2 scope=spfile;
System altered.
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 281018368 bytes
Fixed Size 2095672 bytes
Variable Size 222299592 bytes
Database Buffers 50331648 bytes
Redo Buffers 6291456 bytes
Database mounted.
Database opened.
SQL> select thread#,status,enabled from v$thread;
THREAD# STATUS ENABLED
---------- ------ --------
1 CLOSED PUBLIC
2 OPEN PRIVATE
SQL> select group#,thread#,status from v$log;
GROUP# THREAD# STATUS
---------- ---------- ----------------
4 1 INACTIVE
5 1 CURRENT
6 2 CURRENT
7 2 UNUSED
SQL> Rac环境下：
[oracle@node1 ~]$ crs_stat -t -v
Name Type R/RA F/FT Target State Host
----------------------------------------------------------------------
ora.easy.db application 0/0 0/1 ONLINE ONLINE node1
ora....y1.inst application 0/5 0/0 ONLINE ONLINE node1
ora....y2.inst application 0/5 0/0 ONLINE ONLINE node2
ora....SM1.asm application 0/5 0/0 ONLINE ONLINE node1
ora....E1.lsnr application 0/5 0/0 ONLINE ONLINE node1
ora.node1.gsd application 0/5 0/0 ONLINE ONLINE node1
ora.node1.ons application 0/3 0/0 ONLINE ONLINE node1
ora.node1.vip application 0/0 0/0 ONLINE ONLINE node1
ora....SM2.asm application 0/5 0/0 ONLINE ONLINE node2
ora....E2.lsnr application 0/5 0/0 ONLINE ONLINE node2
ora.node2.gsd application 0/5 0/0 ONLINE ONLINE node2
ora.node2.ons application 0/3 0/0 ONLINE ONLINE node2
ora.node2.vip application 0/0 0/0 ONLINE ONLINE node2
[oracle@node1 ~]$
[oracle@node1 ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.5.0 - Production on Sat Aug 30 17:47:08 2014
Copyright (c) 1982, 2010, Oracle. All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Data Mining
and Real Application Testing options
SQL> desc v$thread
Name Null? Type
----------------------------------------- -------- ----------------------------
THREAD# NUMBER
STATUS VARCHAR2(6)
ENABLED VARCHAR2(8)
GROUPS NUMBER
INSTANCE VARCHAR2(80)
OPEN_TIME DATE
CURRENT_GROUP# NUMBER
SEQUENCE# NUMBER
CHECKPOINT_CHANGE# NUMBER
CHECKPOINT_TIME DATE
ENABLE_CHANGE# NUMBER
ENABLE_TIME DATE
DISABLE_CHANGE# NUMBER
DISABLE_TIME DATE
LAST_REDO_SEQUENCE# NUMBER
LAST_REDO_BLOCK NUMBER
LAST_REDO_CHANGE# NUMBER
LAST_REDO_TIME DATE
SQL> select thread#,status,enabled from v$thread;
THREAD# STATUS ENABLED
---------- ------ --------
1 OPEN PUBLIC
2 OPEN PUBLIC
SQL> show parameter thread
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
parallel_threads_per_cpu integer 2
thread integer 1
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Data Mining
and Real Application Testing options
[oracle@node1 ~]$ ssh oracle@node2
Last login: Mon Aug 25 13:09:51 2014 from node3
[oracle@node2 ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.5.0 - Production on Sat Aug 30 17:48:27 2014
Copyright (c) 1982, 2010, Oracle. All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Data Mining
and Real Application Testing options
SQL> show parameter thread
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
parallel_threads_per_cpu integer 2
thread integer 2
SQL> alter system set thread=1 scope=spfile sid='easy2';
System altered.
SQL> alter system set thread=2 scope=spfile sid='easy1';
System altered.
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Data Mining
and Real Application Testing options
[oracle@node2 ~]$ exit
logout
Connection to node2 closed.
[oracle@node1 ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.5.0 - Production on Sat Aug 30 17:55:54 2014
Copyright (c) 1982, 2010, Oracle. All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Data Mining
and Real Application Testing options
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 205520896 bytes
Fixed Size 2095088 bytes
Variable Size 121636880 bytes
Database Buffers 75497472 bytes
Redo Buffers 6291456 bytes
Database mounted.
Database opened.
SQL> show parameter thread
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
parallel_threads_per_cpu integer 2
thread integer 2
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Data Mining
and Real Application Testing options
[oracle@node1 ~]$ ssh oracle@node2
Last login: Sat Aug 30 17:54:14 2014 from node1
[oracle@node2 ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.5.0 - Production on Sat Aug 30 17:57:00 2014
Copyright (c) 1982, 2010, Oracle. All Rights Reserved.
Connected to an idle instance.
SQL> startup
ORACLE instance started.
Total System Global Area 205520896 bytes
Fixed Size 2095088 bytes
Variable Size 100665360 bytes
Database Buffers 96468992 bytes
Redo Buffers 6291456 bytes
Database mounted.
Database opened.
SQL> show parameter thread
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
parallel_threads_per_cpu integer 2
thread integer 1
SQL> desc gv$log
Name Null? Type
----------------------------------------- -------- ----------------------------
INST_ID NUMBER
GROUP# NUMBER
THREAD# NUMBER
SEQUENCE# NUMBER
BYTES NUMBER
MEMBERS NUMBER
ARCHIVED VARCHAR2(3)
STATUS VARCHAR2(16)
FIRST_CHANGE# NUMBER
FIRST_TIME DATE
SQL> select inst_id,group#,thread# from gv$log;
INST_ID GROUP# THREAD#
---------- ---------- ----------
1 1 1
1 2 1
1 3 2
1 4 2
2 1 1
2 2 1
2 3 2
2 4 2
8 rows selected.
SQL> show parameter thread
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
parallel_threads_per_cpu integer 2
thread integer 1
SQL> select thread#,status,enabled from v$thread
2 ;
THREAD# STATUS ENABLED
---------- ------ --------
1 OPEN PUBLIC
2 OPEN PUBLIC
SQL> alter database add logfile thread 3 group 5 '+DG4' size 50M;
Database altered.
SQL> alter database add logfile member '+DG4' to group 5;
Database altered.
SQL> alter database add logfile thread 3 group 6 '+DG4' size 50M;
Database altered.
SQL> alter database add logfile member '+DG4' to group 6;
Database altered.
SQL> alter database enable thread 3;
Database altered.
SQL> select thread#,status,enabled from v$thread;
THREAD# STATUS ENABLED
---------- ------ --------
1 OPEN PUBLIC
2 OPEN PUBLIC
3 CLOSED PRIVATE
结论：如果我们使用add logifle 语句时，指定的thread大于instancde_number,就会产生private thread(个人猜测),只有private thread的作用，目前尚未发现有特别的用处