Informix locking issue, please help...

Question

To anyone with the inclination to help,
We are using WLS5.1. We have a stateless session bean containing (very simple)
JDBC code. We are using container managed transactions, an isolation level of READ_COMMITTED,
and autoCommit set to false.
Here is the situation : 2 threads almost simultaneously run the following SQL command
on a small table created with LOCK MODE ROW. Note the threads supply different
values for reqID (a unique id).
update msgtable set tread=? where reqID=?
One of the transactions succeeds, the other is rolled back due to
a SQLException : Informix major error code = -244, a minor code of -107.
This error indicates that the second transaction is being denied a lock, and hence
cannot perform the update. This is strange because the lock granted to the succeeding
transaction should be for a different row than the one which failed, however ignoring
this - here is the problem as far as i can tell. By default an Informix session has
a LOCK MODE of NO WAIT - this means if a lock isn't available exactly when requested,
it will cause the transaction requesting the lock to roll-back immediately, which
is unacceptable.
How do I configure a connection pool to do a
'SET LOCK MODE TO WAIT x' (will wait x seconds for a lock to become available) command
when it connects to Informix?
Do I have to write the code that does this myself each time I use an Informix connection?
(Due to the dynamic nature of connection pools, i don't see how i can put this into
a start-up class)
Any help is much appreciated,
Regards,
Serge Monkewitz

Answer 1

Serge Monkewitz wrote:
Hi Joseph,
Thanks so much for the reply, that is excellent news!I'm glad to help.
We are using Weblogic5.1sp10, and the the weblogic informix4 driver.
You're saying we should upgrade to sp12 and use the IBM informix driver? (I did check
their driver documentation, as well as informix documentation and their does not
appear to be a way to to set the lock mode through a property).In general our spX is better than our sp(X-y) so I do recommend them :-)
Separately, I also do recommend Informix's own driver if you have any
problem at all with our Informix driver. Theirs is better.
Before I upgrade our service pack, how do I specify the arbitrary SQL for the pool
connection tests? (I looked at the 5.1 docs as well as the sp12 docs and couldn't
find the relevant section).In the pool definition you have an entry for the testTable in the weblogic.properties
file. Set this as I described below, eg:
testTable=SQL SET LOCK MODE TO WAIT 30,\
testConnsOnReserve=true,\
refreshTestMinutes=99999999,\
I recommend all three lines shown above. The test table setting will do what you
want (for either driver) if the second line is set as shown, and the third line
effectively turns off a periodic asynchronos checker that tests idle connections.
This is unnecessary unless you have a firewall or DBMS that will kill idle connections
after a timeout period.
The docs URL is:
http://www.weblogic.com/docs51/classdocs/conn_pools.html#635172
Joe
>
>
Thanks again,
Regards,
Serge Monkewitz
Joseph Weinstein <[email protected]> wrote:
What version of 5.1? If it's the latest service pack, you can do the following
trick. If the
Informix driver doesn't have a property you can set to make this the default
behavior
(we recommend their driver), then set your connection pool to test connections
at
reserve time. For the 'test table', you can actually specify arbitrary SQL
to be executed.
This will serve perfectly to test the connection and assure this behavior.
Set the test table
string to:
SQL SET LOCK MODE TO WAIT x
The pool will strip off the leading 'SQL ' and execute the rest before giving
you the
connection.
Joe