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ARCH和LGWR进程同步DG日志的区别

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ARCH 和 LGWR 进程同步 DG 日志的区别

我在做 Standby RAC 实验时,起初使用的是 ARCH 传输,后来将其改为 LGWR 传输(实际是 LGWR 分出的小工进程 LNS):

-- 之前的设置
alter system set log_archive_dest_2='SERVICE=mynas ARCH VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=mynas';
-- 修改设置,可以在线修改:
alter system set log_archive_dest_2='SERVICE=mynas VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=mynas';

最直观的就是 LGWR 进程传输可以延迟很低,甚至基本是实时的,即使是 ASYNC,另外还有一些细微的差别。

  • 1.ARCH 进程传输
  • 2.LGWR 进程传输

1.ARCH 进程传输

主库:

SYS@jyzhao1 >select process, client_process, sequence#, status from v$managed_standby;
PROCESS CLIENT_P SEQUENCE# STATUS
--------- -------- ---------- ------------
ARCH ARCH 146 CLOSING
ARCH ARCH 137 CLOSING
ARCH ARCH 147 CLOSING
ARCH ARCH 147 CLOSING

在主库查询可以看到,只有几个归档进程。

备库:

SQL> select process, client_process, sequence#, status from v$managed_standby;
PROCESS CLIENT_P SEQUENCE# STATUS
--------- -------- ---------- ------------
ARCH ARCH 146 CLOSING
ARCH ARCH 113 CLOSING
ARCH ARCH 0 CONNECTED
ARCH ARCH 111 CLOSING
RFS ARCH 0 IDLE
RFS UNKNOWN 0 IDLE
RFS UNKNOWN 0 IDLE
RFS ARCH 0 IDLE
RFS UNKNOWN 0 IDLE
RFS UNKNOWN 0 IDLE
MRP0 N/A 147 WAIT_FOR_LOG
11 rows selected.
SQL> select * from v$standby_log;
GROUP# DBID THREAD# SEQUENCE# BYTES BLOCKSIZE USED ARC STATUS FIRST_CHANGE# FIRST_TIME NEXT_CHANGE# NEXT_TIME LAST_CHANGE# LAST_TIME
---------- ---------------------------------------- ---------- ---------- ---------- ---------- ---------- --- ---------- ------------- ------------ ------------ ------------ ------------ ------------
11 UNASSIGNED 1 0 52428800 512 0 NO UNASSIGNED
12 UNASSIGNED 1 0 52428800 512 0 NO UNASSIGNED
13 UNASSIGNED 1 0 52428800 512 0 NO UNASSIGNED
21 UNASSIGNED 2 0 52428800 512 0 NO UNASSIGNED
22 UNASSIGNED 2 0 52428800 512 0 NO UNASSIGNED
23 UNASSIGNED 2 0 52428800 512 0 NO UNASSIGNED
6 rows selected.

在备库查询可以看到,RFS 中也只有 ARCH 进程,SRLs 也都没有使用,即使指定使用 using current logfile。

2.LGWR 进程传输

主库:

SYS@jyzhao1 >select process, client_process, sequence#, status from v$managed_standby;
PROCESS CLIENT_P SEQUENCE# STATUS
--------- -------- ---------- ------------
ARCH ARCH 149 CLOSING
ARCH ARCH 137 CLOSING
ARCH ARCH 148 CLOSING
ARCH ARCH 149 CLOSING
LNS LNS 150 WRITING

我们发现,使用 LGWR 进程传输,在主库查询可以看到差异,比之前 ARCH 传输多了一个 LNS 的进程,这就是 LGWR 分出来的小工进程。
备库:

SQL> select process, client_process, sequence#, status from v$managed_standby;
PROCESS CLIENT_P SEQUENCE# STATUS
--------- -------- ---------- ------------
ARCH ARCH 148 CLOSING
ARCH ARCH 149 CLOSING
ARCH ARCH 0 CONNECTED
ARCH ARCH 115 CLOSING
RFS ARCH 0 IDLE
RFS UNKNOWN 0 IDLE
RFS UNKNOWN 0 IDLE
RFS ARCH 0 IDLE
RFS UNKNOWN 0 IDLE
RFS LGWR 116 IDLE
MRP0 N/A 116 APPLYING_LOG
PROCESS CLIENT_P SEQUENCE# STATUS
--------- -------- ---------- ------------
RFS LGWR 150 IDLE
RFS UNKNOWN 0 IDLE
13 rows selected.
SQL> select * from v$standby_log;
GROUP# DBID THREAD# SEQUENCE# BYTES BLOCKSIZE USED ARC STATUS FIRST_CHANGE# FIRST_TIME NEXT_CHANGE# NEXT_TIME LAST_CHANGE# LAST_TIME
---------- ---------------------------------------- ---------- ---------- ---------- ---------- ---------- --- ---------- ------------- ------------ ------------ ------------ ------------ ------------
11 UNASSIGNED 1 0 52428800 512 0 NO UNASSIGNED
12 2509089778 1 150 52428800 512 6417408 YES ACTIVE 4026243 10-AUG-17 4050942 10-AUG-17
13 UNASSIGNED 1 0 52428800 512 0 NO UNASSIGNED
21 UNASSIGNED 2 0 52428800 512 0 NO UNASSIGNED
22 2509089778 2 117 52428800 512 2767360 YES ACTIVE 4044272 10-AUG-17 4050945 10-AUG-17
23 UNASSIGNED 2 0 52428800 512 0 NO UNASSIGNED
6 rows selected.

我们发现,使用 LGWR 进程传输,在备库查询可以看到差异,相比之前 ARCH 传输 RFS 中只有 ARCH 进程而言,又多了 LGWR 进程,另外 SRLs 也被正常使用。

alert 日志上也有所区别:

主库:

Thu Aug 10 09:36:43 2017
ALTER SYSTEM SET log_archive_dest_2='SERVICE=mynas VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=mynas' SCOPE=BOTH;
Thread 1 advanced to log sequence 150 (LGWR switch)
Current log# 2 seq# 150 mem# 0: +DATA1/jyzhao/onlinelog/group_2.262.919999045
Current log# 2 seq# 150 mem# 1: +FRA1/jyzhao/onlinelog/group_2.258.919999049
Thu Aug 10 09:36:45 2017
Archived Log entry 287 added for thread 1 sequence 149 ID 0x958da9ee dest 1:
******************************************************************
LGWR: Setting 'active' archival for destination LOG_ARCHIVE_DEST_2
******************************************************************
ARC3: Standby redo logfile selected for thread 1 sequence 149 for destination LOG_ARCHIVE_DEST_2
LNS: Standby redo logfile selected for thread 1 sequence 150 for destination LOG_ARCHIVE_DEST_2
Thu Aug 10 09:59:59 2017
Setting Resource Manager plan DEFAULT_MAINTENANCE_PLAN via parameter
Thu Aug 10 10:00:00 2017
Starting background process VKRM
Thu Aug 10 10:00:00 2017
VKRM started with pid=44, OS id=7493

可以看到,相比之前,多了“LGWR: Setting ‘active’ archival for destination LOG_ARCHIVE_DEST_2”字样。
备库:

Thu Aug 10 09:36:42 2017
Archived Log entry 35 added for thread 1 sequence 148 ID x958da9ee dest 1:
Media Recovery Log +FRA/mynas/archivelog/017_08_10/thread_1_seq_148.301.951644203
Media Recovery Waiting for thread 1 sequence 149
Thu Aug 10 09:36:45 2017
Primary database is in MAXIMUM PERFORMANCE mode
Thu Aug 10 09:36:46 2017
RFS[12]: Assigned to RFS process 28007
RFS[12]: Selected log 11 for thread 1 sequence 149 dbid -1785877518 branch 919999037
RFS[13]: Assigned to RFS process 28005
RFS[13]: Selected log 12 for thread 1 sequence 150 dbid -1785877518 branch 919999037
Thu Aug 10 09:36:47 2017
Archived Log entry 36 added for thread 1 sequence 149 ID x958da9ee dest 1:
Media Recovery Log +FRA/mynas/archivelog/017_08_10/thread_1_seq_149.302.951644207
Media Recovery Waiting for thread 2 sequence 115
Thu Aug 10 09:36:48 2017
Primary database is in MAXIMUM PERFORMANCE mode
RFS[14]: Assigned to RFS process 28009
RFS[14]: Selected log 21 for thread 2 sequence 116 dbid -1785877518 branch 919999037
Thu Aug 10 09:36:49 2017
RFS[15]: Assigned to RFS process 28011
RFS[15]: Selected log 22 for thread 2 sequence 115 dbid -1785877518 branch 919999037
Archived Log entry 37 added for thread 2 sequence 115 ID x958da9ee dest 1:
Media Recovery Log +FRA/mynas/archivelog/017_08_10/thread_2_seq_115.303.951644209
Media Recovery Waiting for thread 1 sequence 150 (in transit)
Recovery of Online Redo Log: Thread 1 Group 12 Seq 150 Reading mem 0
Mem# 0: +FRA/mynas/standbylog/standby_group_12.log
Media Recovery Waiting for thread 2 sequence 116 (in transit)
Recovery of Online Redo Log: Thread 2 Group 21 Seq 116 Reading mem 0
Mem# 0: +FRA/mynas/standbylog/standby_group_21.log
Thu Aug 10 10:02:28 2017
RFS[14]: Selected log 22 for thread 2 sequence 117 dbid -1785877518 branch 919999037
Thu Aug 10 10:02:35 2017
Media Recovery Waiting for thread 2 sequence 117 (in transit)
Thu Aug 10 10:02:35 2017
Archived Log entry 38 added for thread 2 sequence 116 ID x958da9ee dest 1:
Recovery of Online Redo Log: Thread 2 Group 22 Seq 117 Reading mem 0
Mem# 0: +FRA/mynas/standbylog/standby_group_22.log

可以看到多了“(in transit)”字样。

这种 LGWR 传输,即便是默认的 ASYNC,正常延迟也都很低,符合绝大部分场景需要:

SQL> select * from v$dataguard_stats;
NAME VALUE UNIT TIME_COMPUTED DATUM_TIME
-------------------------------- ---------------------------------------------------------------- ------------------------------ ------------------------------ ------------------------------
transport lag +00 00:00:00 day(2) to second(0) interval 08/10/2017 11:43:37 08/10/2017 11:43:35
apply lag +00 00:00:00 day(2) to second(0) interval 08/10/2017 11:43:37 08/10/2017 11:43:35
apply finish time +00 00:00:00.000 day(2) to second(3) interval 08/10/2017 11:43:37
estimated startup time 26 second 08/10/2017 11:43:37
SQL>

可以看到上面的延迟都是 0。实际运维经验,一般 11g ADG,不出网络等其他问题,这个延迟基本为 0。

更多 Oracle 相关信息见 Oracle 专题页面 http://www.linuxidc.com/topicnews.aspx?tid=12

本文永久更新链接地址 :http://www.linuxidc.com/Linux/2017-08/146332.htm

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