DG學習筆記(11)_Log Transport Services

DG學習筆記(11)_Log Transport Services

 

目錄

 

1 Introduction to Log Transport Services

2 Functional overview

3 How to Send Redo Data

4 Using LGWR to Archive Redo Data

5 Network Tuning for Log Transport Services

 

 

1 Introduction to Log Transport Services

 

The log transport services component of the Data Guard environment is responsible for automatic archiving of primary database online redo logs. Once archived, these logs are known as archived redo logs. Log transport services provide for the management of archived redo log permissions, destinations, transmission, reception, and transmission failure resolution.

 

2 Functional overview

 

The archiver process (ARCn) or log writer process (LGWR) can be configured to archive online redo logs to a maximum of 10 destinations.(LGWR也可以歸檔? 是的)

 

Note:

Log transport services to the physical standby database must be configured to use a dedicated server process in managed recovery mode. Although the read-only mode allows a shared server process, you must have a dedicated server once you open the database again in managed recovery mode.(物理Standby必須配置成Dedicated Server Mode)

 

 

3 How to Send Redo Data

 

By default, log transport services use ARCn processes to archive the local online redo log files on the primary database before transmitting the redo data to remote standby destination. ARCn archival processing supports only the maximum performance level of data protection in Data Guard configurations. You must use the LGWR process to transmit redo data to standby locations that operate in other data protection modes.

 

Initialization Parameter

The LOG_ARCHIVE_LOCAL_FIRST initialization parameter, the ARCH attribute on the LOG_ARCHIVE_DEST_n parameter, and the LOG_ARCHIVE_DEST_STATE_n parameter control ARCn archival processing.

 

LOG_ARCHIVE_LOCAL_FIRST (10g) controls when the archiver process transmit redo data to remote standby database destionation.

TRUE:  after the online redo log file is completely and successfully archived to at least one local destination. This is the default value.(先本地再遠端)

FALSE: at the same time the online redo log file is archived to the local destinations.(同時)

 

 

4 Using LGWR to Archive Redo Data

 

If you choose the LGWR process, it will transmit redo data to both the local and remote destinations as the redo is generated on the primary database.(as redo is generated at the primary database, it is also propagated to the remote destination.日常產生的同時也傳輸到Remote Destination,而不像ARCn要先生成歸檔,再傳輸歸檔.)

 

 

5 Network Tuning for Log Transport Services

 

The process of archiving redo logs involves reading a buffer from the redo log and writing it to the archive log location. When the destination is remote, the buffer is written to the archive log location over the network using Oracle Net services.

The default archive log buffer size is 1 megabyte. The default transfer buffer size for Oracle Net is 2 kilobytes.

(歸檔的Buffer Size和Oracle Net 的Buffer Size)

 

The Oracle Net parameter that controls the transport size is session data unit (SDU). This parameter can be adjusted to reduce the number of network packets that are transmitted. This parameter allows a range of 512 bytes to 32 kilobytes.

 

for example:

netserv=(DESCRIPTION=(SDU=32768)(ADDRESS=(PROTOCOL=tcp)(HOST=host) (PORT=1521)) (CONNECT_DATA=(SERVICE_NAME=srvc)(ORACLE_HOME=/oracle)))

 

If you archive to a remote site using high-latency/high-bandwidth connections, you can improve performance by increasing the TCP send and receive window sizes. Use caution, however, because this may adversely affect networked applications that do not exhibit the same characteristics as archiving. This method consumes alarge amount of system resources.

(謹慎使用這個功能選項.)