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From Lukas S├Ągesser ...@paysol.ch>
Subject mysteriously dying connections (Oracle <-> tomcat)
Date Thu, 21 Jun 2001 14:37:41 GMT
hi all!

problem:
--------

database access is managed via a java class that is
instantiated and loaded into each clients session. every
PL/SQL function and/or SQL statement a client needs is
called in a method of this class.
first, a connection is opened, the statement is called,
all resultsets and statements are closed and finally the
connection is closed. (or returned back to the
connection pool if one is used)

the driver we use is the Oracle jdbc ThinDriver (jdbc
driver type 4). after running the system for several
days, dead connections (and as we just discovered, tons
of open cursors) pile up.
eventually the webserver(tomcat) will crash or just
hang.
in the process, access gets slower and slower, there may
be delays of 3 minutes until the webserver (or, perhaps
the database, in which case the webserver would be just
waiting for the db..) gives a response.
after a restart of the webserver or the database or
both, the system runns very well again.

we tried several connection pools. with these, there
were no delays for getting a connection, but the pool
threw timeoutExceptions (i.e. made it visible that there
are hanging connections) and after a few hundred
timeouts the VM crashed with a stack overflow.

the connections seem to get killed/kill themselfes
randomly no matter which function was called. we log the
methods and statements that were called for the
connections that die, but there is just no pattern in
it. thats why we dont find the root of the problem.. is
it the driver ? the database ? the tomcat ?



environment:
----------------

Web Server:
Suse Linux 7.2
Apache Webserver /w Tomcat JSP Engine 3.2 /w SSL

DB Server:
Suse Linux 7.2
Oracle 8i 8.1.7 /w multi-threaded server (MTS)

Backup Server:
Oracle Shadow server



things done:
------------

- linux update
- apache update
- tomcat update
- jdbc thin driver update
(everywhere the newest version)
- tried several connection pools



possible changes:
-----------------

- use OCI drivers instead of thin driver
- use J-serv with GNU_jsp instead of tomcat




every help is welcome, we're frustrated to no ends.
thanks very much in advance!!

l.s├Ągesser


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