For a demo on this topic you can see the following:
Why does it seem that a select over a db link requires a commit after execution?
-- Mark D Powell --
Phone (313) 592-5148
From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of Marc Demlenne
Sent: Tuesday, April 03, 2007 8:43 AM
To: Kerber, Andrew W.
Subject: Re: Remote Select opening transaction
It is ! You can try the following :
- Do a select * from remoteDB.remoteTable@remoteHost (but remoteDB is enought, can be same host)
- Don't commit, rollback or quit. Be carefull not to exit in timeout
- And monitor the RBS. you'll notice that your sqlplus process is locking one of the RBS, and the number of extent will start growing up and up until you'll recah the ORA-01562 error.
I use :
select rn.name, r.curext, t.start_uext, r.extents, t.xidusn, s.sid, s.process, t.start_time
from V$rollstat r, v$rollname rn, V$transaction t, v$session S
WHERE t.addr = s.taddr (+) and t.XIDUSN=r.USN AND r.usn(+) = rn.usn
Exiting your sqlplus (or commit or rollback) will unblock the situation, freeing your RBS. In my case, we use the "OPTIMAL" parameter and see the number of extents immediately reducing to it's optimal value ...
On 4/3/07, Kerber, Andrew W. <Andrew.Kerber@umb.com> wrote:
Hi. I am pretty sure your information is incorrect. I have never seen a select across a db link open a transaction.
From: email@example.com [mailto: firstname.lastname@example.org] On Behalf Of Marc Demlenne
Sent: Tuesday, April 03, 2007 7:08 AM
Subject: Remote Select opening transaction
In Oracle 8, when performing a select query on another database threw DB link, Oracle opens a transaction that could only be closed by commit or rollback. That could be harmful when developers are not aware of this and don't close transaction. (leading to ORA-01562.)
What is the reason of this behaviour ? Is there some docs / faq explaining this ?
Is this feature also common to later versions of Oracle ?
Thanks a lot for any piece of information given,
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