we have a legacy application which uses a access.mdb with hundreds of ODBC-connected tables on a sql-server. the access.mdb contains nothing else than these odbc-connections.

Now we consider to use a virtual sql-servername for these odbc connections and resolve it in the local hosts-file with the ip-address of the real sql-server.

Like this we can easy switch between a test-sql-database server and the the server for production in changing one single entry in the hosts.

EVERYTHING works fine and now comes the question:

Could it be that this is more performant because there is one single point on resolving the sql-server (name or ip-address)? Is there something like a network-cache / DNS-Cache?




If the DNS server is local to your LAN, I doubt you'll see a noticeable improvement from having the entry in the hosts file. However, if you want to be able to switch easily from one SQL Server to another, it's a very convenient and fast solution, especially if the people managing the DNS are not very quick or eager to help.

Windows caches DNS records. In a Command prompt, run

ipconfig -displaydns

to see the content of the DNS cache.

If you want to empty it, to force Windows to request a resolution to the DNS server, run the command:

ipconfig -flushdns

You'll find more information about the DNS cache, how to disable it, and its settings in this article of the Microsoft Knowledge Base.

  • Thanks for your answer but why should i disable DNS-Caching? On the other hand, how works that hosts resolving? – Ice Mar 17 '10 at 10:55
  • As i can see now, testing the command 'ipconfig /displaydns' there is no output about the connected servers like par example an 'arp -a' does. None of the involved servers like sql-server, file-server, exchange and so on, are listed. 'ipconfig /?' doesn't show wheter /displaydns nor /flushdns. Is this an undocumentet hack? – Ice Mar 17 '10 at 14:31
  • Got it: [support.microsoft.com/kb/223413/en-us] but doesn't help any further. – Ice Mar 17 '10 at 14:38

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