[펌][ORACLE] Oracle 11gR2 Grid Infrastructure Single Client Access Name (SCAN)

Oracle 11gR2에 새로 추가된 기능인 SCAN에 대해 간단히 정리합니다.. (까먹기 전에 --;)

Oracle은 새로운 버전이 나올때 마다 새로운 기능들을 추가하는데, 이번에 소개드릴 기능은 SCAN (Single Client Access Name) 입니다. 말 그대로 client에서 server를 접속할 때 여러개의 RAC 노드가 있더라도 하나의 access name을 갖도록 하는 기능입니다. 이 기능은 새로운 노드가 추가되거나 삭제되는 경우에도 적용되며, 사실 이것을 염두에 두고 있습니다. 

새로운 노드의 추가와 삭제와 상관없는 single client access name 이라.. 
딱 클라우드 컴퓨팅ㄱ이라는 단어가 생각나지 않습니다? 

아래의 tns alias 설정은 SCAN 기능을 사용할 경우 client의 tns alias 설정 sample 입니다. 

언듯보면.. 자세히 봐도 single DB 접속하는 tns alias와 동일합니다. 

TEST.ORACLE.COM =
(DESCRIPTION=
(ADDRESS=(PROTOCOL=tcp)(HOST=SCAN-TEST.ORACLE.COM)(PORT=1521))
(CONNECT_DATA=(SERVICE_NAME=11GR2TEST.ORACLE.COM))

)

이전의 RAC에서의 tns alias는 아래와 같이 설정했었습니다. 

TEST.ORACLE.COM =
(DESCRIPTION=
(ADDRESS_LIST=
(ADDRESS=(PROTOCOL=tcp)(HOST=TEST1-vip.ORACLE.COM)(PORT=1521))
(ADDRESS=(PROTOCOL=tcp)(HOST=TEST2-vip.ORACLE.COM)(PORT=1521))
)
(CONNECT_DATA=(SERVICE_NAME=11GR2TEST.ORACLE.COM))




그럼 어떻게 노드의 추가/삭제에도 동일한 access name을 가질 수 있을까요?

각 노드의 listener 앞에 새로운 listener를 두는 겁니다. 이 앞단의 listener들이 뒤의 RAC listener를 보게 됩니다.

11gR2 Grid Infrastructure Single Client Access Name (SCAN) Explained

SCAN Concepts

• Single client access name (SCAN) is the virtual hostname to provide for all clients connecting to the cluster (as opposed to the vip hostnames in 10g and 11gR1).  
• SCAN is a domain name registered to at least one and up to three IP addresses, either in the domain name service (DNS) or the Grid Naming Service (GNS).
• By default, the name used as the SCAN is also the name of the cluster and must be globally unique throughout your enterprise. The default value for the SCAN is based on the local node name. SCAN name must be at least one character long and no more than 15 characters in length, must be alphanumeric - cannot begin with a numeral and may contain hyphens (-). If you require a SCAN that is longer than 15 characters, then select an Advanced installation.
• For installation to succeed, the SCAN must resolve to at least one address.
• SCAN VIP addresses must be on the same subnet as virtual IP addresses and public IP addresses.
• Oracle strongly recommends that you do not configure SCAN VIP addresses in the hosts file. If you use the hosts file to resolve SCANs, then you will only be able to resolve to one IP address and you will have only one SCAN address - be sure to provide a hosts file entry for each SCAN address in hosts file in same order.
• If hosts file is used to resolve SCAN hostname, you will receive Cluster Verification Utility failure at end of installation (see Note: 887471.1 for more details)
• For high availability and scalability, Oracle recommends that you configure the SCAN to use DNS Round Robin resolution to three addresses.
• Because the SCAN is associated with the cluster as a whole, rather than to a particular node, the SCAN makes it possible to add or remove nodes from the cluster without needing to reconfigure clients. It also adds location independence for the databases, so that client configuration does not have to depend on which nodes are running a particular database.
• Clients can continue to access the cluster in the same way as with previous releases, but Oracle recommends that clients accessing the cluster use the SCAN. Clients using the SCAN can also access the cluster using EZCONNECT.
• Grid Infrastructure will start local listener LISTENER on all nodes to listen on local VIP, and SCAN listener LISTENER_SCAN1 (up to three cluster wide) to listen on SCAN VIP(s); 11gR2 database by default will set local_listener to local LISTENER, and remote_listener to SCAN listener.

위의 SCAN에 대한 concept을 정리해보자면 RAC에 대한 virtual hostname 입니다. 이는 DNS에 설정되어 있고 이를 통해 DB에 접속하게 됩니다. failover나 load-balancing은 RAC 각 노드의 listener 들이 담당하게 됩니다.

이 내용은 "Note:887522.1 - 11gR2 Grid Infrastructure Single Client Access Name (SCAN) Explained" 를 참조했습니다

관련 문서와 동영상을 같이 링크 겁니다.  아직 한글로 소개된 자료는 없는 것 같네요.. 

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SINGLE CLIENT ACCESS NAME (SCAN)

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29 Mar 2010 ... Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC)11g Release 2 feature that provides ...
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