2 Replies Latest reply on Oct 17, 2013 4:33 PM by user11989003

    Benefits of SCAN


      I want to find all benefits of using SCAN listeners over using VIP's without SCAN. The following is my summary, along with some comments. I'd like to hear your comments, and please add anything I missed. Thanks.


      * Less typing in a TNS entry.


      * If you add or remove a node, or make a node unavailable or available, you don't need to modify all your clients' TNS entry. But many shops centrally manage TNS (by periodically distributing a standard tnsnames.ora to all clients, placing the file on a shared drive, using OID or Oracle Names server, etc). This benefit is minimized.


      * Because SCAN is tied to 3 IPs, DNS provides round-robin on the client side. If you use VIP's without SCAN, you have to remember to add load_balance=yes to the TNS stanza to have the same effect.


      * Some clients have trouble accepting more than one database host entry in their configuration. SCAN is a life saver.


      * If you use policy-managed databases, SCAN is mandatory.


      * Installation of RAC requires SCAN. But you can choose to not use it later, or even disable it.


      Disadvantage or caution in using SCAN is not in this list.

        • 1. Re: Benefits of SCAN
          Simo Kemppinen

          Your list is good but here is a couple of thoughts:


          If client is using version older than 11.2 then you still need to add several IPs in TNS entry (even server is SCAN capable) .

          This is because the SCAN was introduced in version 11.2.


          There is also new features for SCAN in Oracle 12c:

          - SCAN and Oracle Clusterware managed VIPs now support IPv6 based IP addresses.

          - SCAN is by default restricted to only accept service registration from nodes in the cluster.

          - SCAN supports multiple subnets in the cluster (one SCAN per subnet).


          Here you can find good document about SCAN:


          • 2. Re: Benefits of SCAN

            Thanks Simo. I was aware of the pre-11.2 client issue. I just wanted to focus on benefits of SCAN. Thanks for listing the 12c enhancements. I read the PDF document before and have a copy of its old version. The new version has expanded a lot. The support for multiple subnets may be useful in our shop.


            I'm going to post a message about overhead of SCAN and ask for comments.