DataGuard on Oracle 11g初步介紹(2)

DataGuard的三種服務
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Redo Transport Services(RTS)
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負責把primary database的redo資料傳輸到standby database上去.一個primary可以帶9個standby,standby database可以邏輯的也可以是物理的,傳輸的方式,就是primary將redo data傳輸到其中的一個standby資料庫上,然後這個standby再繼續將他所接受到的redo data傳送到其他剩餘的standby上.這樣的方式減輕了primary的壓力. 傳輸是通過Oracle Net實現的

1.Transmit redo data from the primary to standby in the configuration

2.Manage the process of resoving any gaps in the archived redo log file due to a network failure

3.Automatically detect missing or corrupted archived redo log files on a standby and automatically retrieve replacement archived redo log files from the primary database or another standby database.

Apply Services(AS)
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用於在standby資料庫中進行apply日誌檔案.這個日誌可以是歸檔日誌,如果想要primary database的任何改變都立即影響到standby database,則可以直接從standby的redo log file在他滿的時候線上apply,而不必等到standby redo log file archived的時候在apply standby資料庫.

The redo data transmitted from the primary database is written to the standby redo log on the standby database,Apply services automatically apply the redo data on the standby database to maintain the consistency with the primary databasein Oracle 11G,it also allows read-only access to the data
Notice that the main difference between physical and logical standby database is the manner in which apply service apply the archived redo data

在physical standby會以redo apply standard techniques(通常Oracle recover的方式)的方式進行primary和standby進行block對block的redo apply.在Oracle11g中,在同時在apply的時候,客戶端還能query(read only).

而logical standby會通過apply service對接收到的redo data以sql statement為目標進行transforms,對已經transforms成的SQL Statement,以SQL Execution的方式來使得主備一致.同時和physical standby不同的是,客戶端可以以read write的方式對資料庫進行操作.

Role Transitions
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primary和standby的互相切換的服務.
有兩種
switchover(人為,no loss data)
failover(被動,dba can configure the dataguard to ensure no loss data)

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/12361284/viewspace-63894/，如需轉載，請註明出處，否則將追究法律責任。