RE: Jboss/Oracle/select 1 form dual
- From: "Pradeep Chetal" <Pradeep.Chetal@xxxxxxxxxxxxxx>
- To: <nigel.cl.thomas@xxxxxxxxxxxxxx>, "Oracle-L Freelists" <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 8 May 2009 06:05:10 -0400
Well, in this case - it is Jboss who will be doing it - since it is the
Jboss Validation string - to close idle connections that are not being
used.
I don't think it is in the JDBC driver itself.
I will find out more.
-- Pradeep
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Nigel Thomas
Sent: Friday, May 08, 2009 5:35 AM
To: Oracle-L Freelists
Subject: Fwd: Jboss/Oracle/select 1 form dual
Martin
Well yes, but millions of times a day (around 800k times per hour in my
example, on a system simulating 2000 concurrent users)? The same error
would be returned from SELECT 1 FROM DUAL or your real application SQL;
so why don't the JDBC driver writers deal with the problem when it is
encountered in the first real application SQL call rather than introduce
an overhead call? IMHO it's just because it's "easier" for them - and
not much easier anyway, as they still need to build error handling into
all the later calls (including connection problems).
The only justification for a keep-alive call is if there has been a long
delay since the last use of a connection, ie if it has been sitting idle
in the connection pool for many minutes/hours; NOT if the pooled
connection is being reused rapidly. But a keep-alive would ideally be
while the connection was idle in the pool - and not when it is assigned
to an application thread which wants to do real application work.
Regards Nigel
2009/5/8 Martin Busik <martin.busik@xxxxxxxx>
> Personally, I would shoot anyone who configures a pointless
additional
> select statement to check connectivity; I blogged on
>
it<http://preferisco.blogspot.com/2006/04/is-this-oracle-wtf.html>a
> couple of years ago and it has come up several times on this
list. But
> that's another matter.
It may become quite hard to find the one, who is doing a
"pointless
additional query".
The JDBC interface contains no ping (or isAlive or similiar)
method.
Connection pool implementations rely on the JDBC interface, so
to check if a
connection
is valid/usable, they can only execute standard conform methods,
typically a
"select null from dual".
Without a connection check, application users (and in the next
steps admins
and developers) are
bored with more or less regular errors ("The first user on
monday morning
gets this exception")
So, a "select null from dual" is the least evil one can
choose...
SCNR,
Martin
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Pradeep Chetal
Sr. Director - Infrastructure Architecture
Mformation Technologies Inc.
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