I find the documentation on both SCAN addresses and TNSNames entries is good
but is still missing some details.
I have a two node RAC cluster:
$ srvctl status scan_listener
SCAN Listener LISTENER_SCAN1 is enabled
SCAN listener LISTENER_SCAN1 is running on node <NODE 2>
SCAN Listener LISTENER_SCAN2 is enabled
SCAN listener LISTENER_SCAN2 is running on node <NODE 1>
SCAN Listener LISTENER_SCAN3 is enabled
SCAN listener LISTENER_SCAN3 is running on node <NODE 1>
My DNS resolves my SCAN address to 3 different IPs (and I can confirm DNS
round-robin is working, the order is different everytime):
$ nslookup dm01-scan.<suffix>
Address: <IP 1>
Address: <IP 2>
Address: <IP 3>
My TNSNames entry is very basic:
(ADDRESS = (PROTOCOL = TCP)(HOST = dm01-scan.<suffix>)(PORT = 1521)))
(CONNECT_DATA = (SERVICE_NAME = <service name>)
We had a crash on one of the nodes (at least it looks like only one) and some
of my processes could not establish a connection to the database. If I was
unlucky, I *think* this means 2 out of my 3 scan listeners was not working.
So I'd like to understand the behavior on the client side when that happens.
What I suspect happened was when my client attempted to connect to the
database, DNS returned a bad IP first, and my client connection failed and
If so, would supplying retry and delay parameters mitigate this issue? More
importantly, if I do not supply these parameters, what's the default behavior
and where is that documented? What if it keeps returning a bad IP first?
Also, in the event of a sudden disconnect of an ALREADY established
connection, is there any TNSNames parameters I can supply to ask the process
to either "pause and wait for the database to come back" or "re-establish your
connection to the same scan address again"? Could I perhaps use the "failover"
parameter but have the failover address just be the same scan address?
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