Re: SCAN addresses and TNSNames
Date: Wed, 2 Oct 2019 18:13:19 +0000
Message-ID: <1723223.WoCVAXJPKe_at_wbeldma>
Assuming it was <NODE 1> that crashed, are you suggesting if I happened to check on <NODE 2> at that time, I would have seen:
$ 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 2> SCAN Listener LISTENER_SCAN3 is enabled SCAN listener LISTENER_SCAN3 is running on node <NODE 2>
And my DNS would have punted all three IPs to <NODE 2>?
How do I verify whether or not this actually occurred?
The client is definitely configured to hit the scan address. That is not in question.
On Wednesday October 2 2019 06:07:22 PM Neil Chandler wrote:
> The scan listener should fail over to the surviving node, so it should be
> presenting all 3 vip’s from that node.
> I’d check that happened, and also that the client is pointing at the scan
> listener.
> Neil.
> sent from my phone
>
>
> > On 2 Oct 2019, at 18:51, William Beldman <wbeldma_at_uwo.ca> wrote:
> >
> > 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>
> > Server: 127.0.1.1
> > Address: 127.0.1.1#53
> >
> > Name: dm01-scan.<suffix>
> > Address: <IP 1>
> > Name: dm01-scan.<suffix>
> > Address: <IP 2>
> > Name: dm01-scan.<suffix>
> > Address: <IP 3>
> > =====
> >
> > My TNSNames entry is very basic:
> > =====
> > (DESCRIPTION =
> > (ADDRESS_LIST =
> > (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
> >
gave up.
> >
> > 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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