During this last time, I have seen more Exalogic customers using SCAN, so decided to write a brief article about it, although there is a lot of documentation from Oracle about it (but not related to Exalogic itself).
Single Client Access Name (SCAN) is a JDBC driver feature that provides a single name for clients to access any Oracle Database running in a cluster. Some of its benefits and advantages include:
- Client’s connect information does not need to change if you add or remove nodes or databases in the cluster
- Fast Connection Failover (FCF)
- Runtime Connection Load-Balancing (RCLB)
- Can be implemented with MultiDataSource or GridLink
- It can also be used with Oracle JDBC 11g Thin Driver (this is clearly explained on MOS Note 1290193.1)
In the particular case of Exalogic, a typical architecture, widely used by customers, is having it connected to an Exadata machine (which hosts the database) through InfiniBand. Obviously the SCAN feature can be used within this Engineered Systems architecture. As a matter of fact, GridLink is part of the Exalogic-specific enhancements of Weblogic.
Some facts to keep in mind when using it:
- SCAN feature is supported on JDBC version 188.8.131.52 and above
- Just as any situation when a connection to database is involved, need to be careful that firewalls may cause some network adapter or timeout issues, which must be solved so the connection can be established
- If using VIP hosts, instead of cluster configuration having the short host name for the VIP hosts, you should set LOCAL_LISTENER to the fully qualified domain name (e.g. node-VIP.example.com):