-----Original Message-----
From: Robert Turner <rtur...@e-djuster.ca.INVALID>
Sent: Friday, August 8, 2025 1:32 AM
To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: How to access a REST service
(sorry for any errors, I'm bashing this out quickly on my phone before going to
bed)
On Fri, Aug 8, 2025, 00:59 Daniel Schwartz <d...@danielgschwartz.com> wrote:
Hello Chuck,
You are correct, I only catch SQL exceptions. I have modified my code
so that the Connection object will be closed if an SQL exception is
thrown, but I wasn’t aware that there are other types of exceptions
that I should look for. I will look into this.
I would encourage entering "avoid java resource leak" into Google and reading the "AI"
generated details or any other articles that come up. The "AI" description it gave me was a
reasonable overview of what we are trying to convey to you and how to resolve it.
Unchecked exceptions can be thrown and the compiler will not warn about it.
This may be the issue, but it it not guaranteed, but it definitely is a
potential and obvious problem with the code.
You need to ensure that everything related to the connection (connection,
ResultSet, Statement, PreparedStatement) are also released (closed) or they
will retain references to the connection and the connection may not be returned
to the pool.
As previously mentioned by others, using try-with-resources for all of these
objects is strongly recommended to avoid leaks. If you are uaing older Java
(consider upgrading), you will need to use finally blocks instead (as
previously mentioned by others).
Unfortunately, you have only posted a portion of the code, and it may be the
case that it the problems stems from elsewhere (like where you make the
queries, or anywhere else that obtains a connection).
It should be easy to get a tool to analyze the code (say your IDE (if you use
one), PMD, Spotbugs, Sonarqube, etc.) and they would likely point out all the
potential resource leaks. Many IDEs, such as Intellij IDEA, also provide such
analysis built in. They basically look for any object derived from AutoClosable
and ensure you are closing the object in a finally clause (or in all potential
code paths). If you aren't, you have a leak.
However, I don’t think that this is causing a memory link, since my
code has always run perfectly without throwing any exceptions at all,
as far as I know.
You may not know. The container (Glassfish or Tomcat) often catches them and
unless you are checking their logs, you may not see any evidence of them.
But I’m beginning to wonder if my “close” operation is actually being
recognized by Glassfish. It seems possible that this is not being
communicated to Glassfish, and the Connection object continues to be
marked as being in use. This would be a leak. But I don’t know if
this is happening.
It's certainly possible that some behaviour of the container and it's pooling
system is exasperating your issue, but I strongly doubt the container is at
fault. It is almost guaranteed to be your code.
There are other possibly issues with your code, but these are less "critical"
than your leaks, but could also be a potential source of issues.
Namely you have static Global's that are not protected against concurrency, and the
containers typically run each request in separate threads. You could be creating more
than one instance of your "singleton" as a result.
Dan
From: Chuck Caldarale <n82...@gmail.com>
Sent: Thursday, August 7, 2025 11:52 PM
To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: How to access a REST service
On 2025 Aug 7, at 21:43, Daniel Schwartz <d...@danielgschwartz.com
<mailto:d...@danielgschwartz.com>> wrote: > > I have just posted
everything again, this time with a few modifications. You say, "Last
time you posted it, it was prone to leaking connection."
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On 2025 Aug 7, at 21:43, Daniel Schwartz <d...@danielgschwartz.com
<mailto:d...@danielgschwartz.com>> wrote:
I have just posted everything again, this time with a few
modifications. You say, "Last time you posted it, it was prone to
leaking connection." Could you say more exactly where you see saw the leak?
You only catch errors of the type SQLException, which means anything
else will lose the connection. This is the reason you should always
use try - catch - finally (or the newer with-resources syntax) around
database manipulations, as recommended in Chris’ blog post.
- Chuck
Thanks,
Dan Schwartz
-----Original Message-----
From: Robert Turner <rtur...@e-djuster.ca.INVALID<mailto:
rtur...@e-djuster.ca.INVALID>>
Sent: Thursday, August 7, 2025 5:07 PM
To: Tomcat Users List <users@tomcat.apache.org<mailto:
users@tomcat.apache.org>>
Subject: Re: How to access a REST service
Dan,
On Thu, Aug 7, 2025 at 5:01 PM Daniel Schwartz
<d...@danielgschwartz.com
<mailto:d...@danielgschwartz.com>>
wrote:
Hello Chris,
Thank you for your reply, but I'm still unsure. You seem to be
implying that I have a memory leak, i.e., many connection objects
being created that are not being closed. However, I really don't
think this is happening. My code closes each connection
immediately
after using it.
Maybe post your code again. Last time you posted it, it was prone to
leaking connections. If it hasn't changed, that is likely your problem.
My understanding is that the only way the maximum pool size of X,
whatever that is, would be a limitation is if there was an attempt
to
create X+1 simultaneous connections. When you do this in
Glassfish,
it outputs an error message saying that no more connections can be
created and then crashes. You have to go back in and manually
restart
it.
I believe that the essential problem, as explained in a previous
email
to Rob Sargent, is that I'm getting several hundred database
requests
per day from web crawlers. I just spent some time reading through
my
ngnix access.log and found that the vast majority of these are from
GoogleBot.
My guess it that, due to a time lag between opening and closing
connections, many connections will be opened simultaneously. This
is
why a small pool size won't work.
Also, I'm advised to not block the web crawlers because this
assists
with SEO. My understanding is that you just have to live with this.
I don't think there is an issue with my code. The only answer I
can
come up with is to have a large maximum pool size, larger that the
expected number of simultaneous accesses.
There is almost definitely a problem with your code (unfortunately),
or
your database requests are very slow and triggered by any connection.
We run servers that handle much more traffic than you are describing
and
make thousands of DB requests per minute, and we rarely go over 10 DB
connections being used at a time.
There is almost for sure something leaking in your code. This is
very
unlikely to be a problem with the pooling ("select isn't broken"). You
are looking for unlikely causes to the problem.
I originally wrote to this email list because I was thinking of
shifting from Glassfish to Tomcat, and was trying to learn how to
do
this. I think I do know how to do this now, and might try doing this.
My understanding is that the connection pooling that works with
Tomcat
doesn't have that same limitation as Glassfish, and one can have
connections that exist outside the pool. This would resolve the
issue
I'm currently having with Glassfish.
Best regards,
Dan Schwartz
...snip..
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