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RE dblink:

From: Stephane Faroult <>
Date: Fri, 02 Jun 2000 17:48:38 +0200
Message-Id: <>


   dblinks are the only way with SQL*Plus to open several connections at once. Useful for comparing schemas between two instances, for example (select object_name from user_objects_at_here minus select object_name from user_objects_at_there), or data. Your idea of a global collector is quite valid - see OEM. I personally dislike GLOBAL_NAME=TRUE because I see no reason why the database link name should be the same as the instance name - from an applicative point of view, you may need to know that the data is managed by another application, but the instance or database name belongs to the nuts and bolts category. If you can avoid GLOBAL_NAME=TRUE (not always possible - if you are using replication for instance) ... If you are interested in the topic of naming dblinks, there is a paper in the library section of our site.

   A loopback dblink forces you to pass by (some) SQL*Net layers, so may be a way to test things. It is also a protection against environmental hazards, eg improperly set or unset ORACLE_SID, or set TWO_TASK.


  Stephane Faroult
  Oriole Corporation
  Voice:  +44  (0) 7050-696-269 
  Fax:    +44  (0) 7050-696-449 
  Performance Tools & Free Scripts
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> Folks,
> I have been playing around with dblink creation and they are created.
> The questions I have are
> When is a dblink useful?
> What benefits does a dblink have over a call at the OS level
> with sqlplus user/passwd_at_aliasname?
> Background about my question...
> I have a script a former dba implemented here at my work.
> It checks extents. It is a solid script but he calls a loopback dblink
> on the machine the rdbms resides.
> So it gets me wondering if in the init.ora file the global_names=true is a
> security risk and what a loopback link would get him.
> The only thing I can think of is to set up one UNIX box with a main work
> tablespace in which all the calls and information is gathered
> (possibly even update meta tables).
> He didn't implement such a thing, but it got me thinking along those lines
> just the same.
> Feedback?
Received on Fri Jun 02 2000 - 10:48:38 CDT

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