Re: Question about db links and tnsnames.ora

Can anyone recommend a good book (or even an article) on how to configure a tnsnames entry and what the corresponding sqlnet.ora should contain?

I've been through the manuals and I think that I have a handle on it but I've never had the slightest bit of Oracle training on the subject.

What I've seen is that many (if not most) DBAs copy an existing entry and edit it with the new sid, port, and ip address.

At a recent job we had a snapshot database with a database link to one side of a RAC cluster. If that side went down the refreshes would fail and my predecessor would drop the database link and recreate it pointing to the working side of the RAC. I finally figured out how to make the link with automatic failover but I couldn't find any good documentation, especially one with an example.

create database link failover connect to scott identified by tiger using '(DESCRIPTION_LIST=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=
(PROTOCOL=TCP)(HOST=xx.xx.xx.x1)(PORT=15xx)))
(CONNECT_DATA=(SID=side1)(failover_mode=(type=SESSION)(method=BASIC))))
(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=xx.xx.xx.x2)
(PORT=15xx)))(CONNECT_DATA=(SID=side2)(failover_mode=
(type=SESSION)(method=BASIC)))))'

There is a limit to how long the "using" token can be. This approaches it. I usually don't have spaces or carrige returns but I've formatted this a little for readability.

I am serious about wanting to find out why this works. It does, but I think that I got lucky and picked the right set of parameters. Is there a white paper, perhaps, that explains what goes with what and what the entries in sqlnet.ora would be? Ditto for the entries in listener.ora. I've set up automatic failover on a listener as well but again it was a lot more hard work than I think it should be.

I haven't found OEM generated entries to be completely satisfactory. Too often they don't work or, if they do, then some other entry doesn't. Personally I find this to be one of the least documented aspects of a DBA's work. Have I just been looking in all the wrong places?

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