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