How does client connect to RAC

Question

I'm confused how client connect to RAC,
1) According to this:
http://www.datadirect.com/developer/odbc/odbc_oracle_rac/connecting/index.ssp
"a ServiceName exists for the entire Oracle RAC system. When an application uses the Oracle RAC system's ServiceName, the Oracle RAC system appears to be a single Oracle instance to the application"
so, seems client just make sure using service name instead of SID, it will be connect to RAC. the URL format is same as single non-RAC enviroment
2) however,according to this:
http://forums.sun.com/thread.jspa?threadID=5274308
The URL need to be:
jdbc:oracle:thin:@(DESCRIPTION=(LOAD_BALANCE=on)
(ADDRESS=(PROTOCOL=TCP)(HOST=host1) (PORT=1521))
(ADDRESS=(PROTOCOL=TCP)(HOST=host2) (PORT=1521))
(CONNECT_DATA=(SERVICE_NAME=service)))
this make RAC connect URL differenct from single non-RAC enviroment
if so, with this format, how does SQL developer connection set up? since you can only specify one host in connection properties configuration?
if so, adding a node will require all of client modify connect url?
3) my understanding is client only need to specify VIP to any one of node, and speicify global service name (all node should share same service name), this will make RAC connection setup (similar to above (1)), but I'm not sure if my understanding correct or not in the following senario:
-- a) what if client using public ip (not VIP) to one of node, but using global service name?
-- b) what if client using VIP to one of node, but using it's SID instead of global service name?
-- c) what if client using public ip (not VIP) to one of node, and using it's SID?
please clarify how does client connect to RAC?
Thank you!

Answer 1

Very good question.
You have asked in a certain way which tells me you have done lot of research.
Any how:-
Remember no matter how convoluting it looks it is the same.
1 Tns Entry
If you add a node then yes you have to publish it.
There are other alternatives such as Oracle Names [old]
internect directory , ldap and so on, beyond the scope of this discussion.
1)
TNSNAME Entry
RAC.WORLD=
DESCRIPTION=DESCRIPTION=(LOAD_BALANCE=on)
(ADDRESS=(PROTOCOL=TCP)(HOST=host1) (PORT=1521))
(ADDRESS=(PROTOCOL=TCP)(HOST=host2) (PORT=1521))
(CONNECT_DATA=(SERVICE_NAME=service))
Now see The same string from DESCRIPTION onwards goes to jdb thin client, it
is the same thing...
Also the host1 host2 are all VIPS'
Also you need failover , load balance thingies in there
-- a) what if client using public ip (not VIP) to one of node, but using global service name?
non vip, Test it out, tns should hop over it .
but TAF /FAN won't work.
-- b) what if client using VIP to one of node, but using it's SID instead of global service name?
You have to use SERVICENAME, if you are using SID then you are pretty
much connecting to 1 node.
-- c) what if client using public ip (not VIP) to one of node, and using it's SID?
Then you are using 1 node rac.