RE: Which query is best?
- From: "Dunbar, Norman" <norman.dunbar@xxxxxxxxxxxxxxxxxxxxxxxxx>
- To: "oracle-l" <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 15 Dec 2009 10:13:25 -0000
Hi Syed,
>> Exactly, we are in the same situation where two or more
>> session waiting for each others, waiting on event 'enq: TX -
>> row lock contention'.
This isn't a deadlock then. See
http://qdosmsq.dunbar-it.co.uk/blog/?p=192 for a description of what
happens during a deadlock.
What you definitely have (as described above) is a situation where the
session that selects for update is locking out the other session(s)
until such time as it commits or rolls back any changes it may have
made. Until such time as that happens, the row(s) locked in the select
for update will remain locked.
It may be possible, as Stephane has pointed out, that your select locks
more than one row in the table. Good advice there and it would be wise
to check if this is the case because you may find that you are locking
out more than one row and that could be causing your long enqueue waits
as you block other sessions that you may not need to block.
Cheers,
Norman.
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