Oracle DataGuard物理備庫的資料模式

在DataGuard中資料保護模式要按照需求來設定

在所有的配置中都是用效能換資料的安全，要麼就是用資料的安全層級來換效能。

1.資料的保護模式
第一種：最大限度保護資料
Maximum availability： This protection mode provides the highest level of data protection that is possible without compromising the availability of a primary database. With Oracle Data Guard, transactions do not commit until all redo data needed to recover those transactions has either been received in memory or written to the standby redo log (depending upon configuration) on at least one synchronized standby database. If the primary database cannot write its redo stream to at least one synchronized standby database, it operates as if it were in maximum performance mode to preserve primary database availability until it is again able to write its redo stream to a synchronized standby database.

This protection mode ensures zero data loss except in the case of certain double faults, such as failure of a primary database after failure of the standby database.

--先將log寫入到記憶體或者一個備庫歸檔，然後執行事務，除了雙方同時故障的意外。

第二種：最大效能
Maximum performance： This is the default protection mode. It provides the highest level of data protection that is possible without affecting the performance of a primary database. This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log. Redo data is also written to one or more standby databases, but this is done asynchronously with respect to transaction commitment, so primary database performance is unaffected by delays in writing redo data to the standby database(s).

This protection mode offers slightly less data protection than maximum availability mode and has minimal impact on primary database performance.

--預設的保護方式，先將事務執行，然後記錄到log，然後同步到備庫，對主庫iude影響非常小

第三種：資料0丟失
Maximum protection： This protection mode ensures that no data loss will occur if the primary database fails. To provide this level of protection, the redo data needed to recover a transaction must be written to both the online redo log and to the standby redo log on at least one synchronized standby database before the transaction commits. To ensure that data loss cannot occur, the primary database will shut down, rather than continue processing transactions, if it cannot write its redo stream to at least one synchronized standby database.

--當事務提交後，將log先提交到備庫，關閉主庫其他的事務，然後執行事務，完畢後執行下一個事務

2.修改方式（資料保護由主庫參數操控）
注意：在主庫操作

按資料包戶程度排序

maximize protection <  maximize availability < maximize performance

SQL> select protection_mode,protection_level from v$database;

PROTECTION_MODE           PROTECTION_LEVEL
------------------------------------------------------------ ------------------------------------------------------------
MAXIMUM PERFORMANCE          MAXIMUM PERFORMANCE

SQL> alter database set standby database to maximize availability;

資料庫已更改。

SQL> select protection_mode,protection_level from v$database;

PROTECTION_MODE                          PROTECTION_LEVEL
------------------------------------------------------------ ------------------------------------------------------------
MAXIMUM AVAILABILITY                        RESYNCHRONIZATION                //沒生效

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