OGG Checkpoint 详解
定位中断的位置，下次启动从中断的位置开始恢复。
1.target 端配置；
2.一条记录对应一个replicat
一. Extract Checkpoints
(1) Extract read checkpoints
（1） Startup checkpoint --ogg启动的时候创建
当Extract 进程启动的时候，会创建startup checkpoint，用来记录此时record的相关信息。该 checkpoint 是第一个checkpoint。
startup checkpoint的统计信息包含如下内容：
（1） Thread #: 创建checkpoint 的thread编号。
（2） Sequence #:创建checkpoint 时对应的sequence 号码。 --list archive log;
（3） RBA: 创建checkpoint 时，redo log 里面record 的relative byte address。
（4）Timestamp: 创建checkpoint 时record对应的timestamp。
（5）SCN: 创建checkpoint 时 record 对应的system change number 。
（6）Redo File: 创建checkpoint 时record对应的事务日志路径。
2 ) Recovery checkpoint
recover checkpoint 记录的是data source（online redo log 或者归档中）中Extract 最久没处理的record的位置。 该checkpoint 的统计信息和startup checkpoint一样。
3) Current checkpoint
current checkpoint 是data source中Extract 最后一次读取的record的位置。
GGSCI (ogg02) 4> info ext1
EXTRACT EXT1 Last Started 2014-12-27 17:42 Status RUNNING
Checkpoint Lag 00:00:00 (updated 00:00:04 ago)
Process ID 31621
Log Read Checkpoint Oracle Redo Logs
2014-12-27 18:06:05 Seqno 15, RBA 18128896
SCN 0.1142344 (1142344)
Seqno 和 RBA 会变，说明ogg是在工作的。
GGSCI (ogg02) 5> info ext1,showch
EXTRACT EXT1 Last Started 2014-12-27 17:42 Status RUNNING
Checkpoint Lag 00:00:00 (updated 00:00:00 ago)
Process ID 31621
Log Read Checkpoint Oracle Redo Logs
2014-12-27 18:11:06 Seqno 15, RBA 18188800
SCN 0.1142472 (1142472)
Current Checkpoint Detail:
Read Checkpoint #1
Oracle Redo Log
Startup Checkpoint (starting position in the data source):
Thread #: 1
Sequence #: 11
RBA: 7646224
Timestamp: 2014-12-27 16:20:48.000000
SCN: 0.1136079 (1136079)
Redo File: /oradata/ogg02/redo02.log
Recovery Checkpoint (position of oldest unprocessed transaction in the data source):
Thread #: 1
Sequence #: 15
RBA: 18187792
Timestamp: 2014-12-27 18:09:41.000000
SCN: 0.1142443 (1142443)
Redo File: /oradata/ogg02/redo03.log
Current Checkpoint (position of last record read in the data source):
Thread #: 1
Sequence #: 15
RBA: 18188800
Timestamp: 2014-12-27 18:11:06.000000
SCN: 0.1142472 (1142472)
Redo File: /oradata/ogg02/redo03.log
Write Checkpoint #1
GGS Log Trail
Current Checkpoint (current write position):
Sequence #: 4
RBA: 1755
Timestamp: 2014-12-27 18:11:43.251745
Extract Trail: /u01/zt/dirdat/lt
Trail Type: RMTTRAIL
Header:
Version = 2
Record Source = A
Type = 10
# Input Checkpoints = 1
# Output Checkpoints = 1
File Information:
Block Size = 2048
Max Blocks = 100
Record Length = 2048
Current Offset = 0
Configuration:
Data Source = 3
Transaction Integrity = 1
Task Type = 0
Status:
Start Time = 2014-12-27 17:42:32
Last Update Time = 2014-12-27 18:11:43
Stop Status = A
Last Result = 400
二.Extract write checkpoints
该checkpoint包含如下信息：
（1）Sequence #: checkpoint 正在写的trail 文件的序列号。
（2）RBA: 创建checkpoint 时trail文件里record 的relative byte address。
（3）Timestamp: 创建checkpoint 时record对应的timestamp。
（4）Extract trail: trail 文件的路径。
（5）Trail Type: 标识trail 文件类型。有2个值：
EXTTRAIL：表示该trail 是本地的trail，文件由OGG进程直接写如本地disk。
RMTTRAIL：表示是远程的trail，该文件不会写入本地的磁盘，而是传到远端的的OGG上，在有远端OGG的collector 进程写disk。
比如pump 进程，里面就会写RMTTRAIL。
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target 端
GGSCI (ogg04) 1> info rep1
REPLICAT REP1 Last Started 2014-12-27 14:07 Status RUNNING
Checkpoint Lag 00:00:00 (updated 00:00:01 ago)
Process ID 26088
Log Read Checkpoint File /u01/zt/dirdat/lt000004
2014-12-27 16:49:03.408880 RBA 1755
GGSCI (ogg04) 2> info rep1,showch
REPLICAT REP1 Last Started 2014-12-27 14:07 Status RUNNING
Checkpoint Lag 00:00:00 (updated 00:00:07 ago)
Process ID 26088
Log Read Checkpoint File /u01/zt/dirdat/lt000004
2014-12-27 16:49:03.408880 RBA 1755
Current Checkpoint Detail:
Read Checkpoint #1
GGS Log Trail
Startup Checkpoint (starting position in the data source):
Sequence #: 3
RBA: 20259
Timestamp: 2014-12-27 14:06:57.000000
Extract Trail: /u01/zt/dirdat/lt
Current Checkpoint (position of last record read in the data source): --最后一次读取文件的位置
Sequence #: 4
RBA: 1755
Timestamp: 2014-12-27 16:49:03.408880
Extract Trail: /u01/zt/dirdat/lt
Header:
Version = 2
Record Source = A
Type = 1
# Input Checkpoints = 1
# Output Checkpoints = 0
File Information:
Block Size = 2048
Max Blocks = 100
Record Length = 2048
Current Offset = 0
Configuration:
Data Source = 0
Transaction Integrity = -1
Task Type = 0
Database Checkpoint:
Checkpoint table = ggs.checkpoint
Key = 982417365 (0x3a8e7fd5)
Create Time = 2014-12-27 10:46:19
Status:
Start Time = 2014-12-27 14:07:31
Last Update Time = 2014-12-27 17:03:30
Stop Status = A
Last Result = 400
GGSCI (ogg04) 3> info rep1 --看rba是否有变化
REPLICAT REP1 Last Started 2014-12-27 14:07 Status RUNNING
Checkpoint Lag 00:00:00 (updated 00:00:08 ago)
Process ID 26088
Log Read Checkpoint File /us01/zt/dirdat/lt000004
2014-12-27 16:49:03.408880 RBA 1755
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停的时候确保两边都事物都提交了。 info 一下看看
②. data dump进程：将队列数据发送到目标
好处：① .预防网络和源库的故障；
②. 可以对数据进行过来和转换；
③.synchronize方式从多个源库上合并数据到一个中心库；
④. synchronize方式将一个源库数据传到多个目标库;
转：http://blog.csdn.net/zhengwei125/article/details/46503403
