(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." > NkdkJdXPPEBannerStart > Be Careful With This Message > From (Chuck Caldarale <n82...@gmail.com>)< > https://godaddy1.cloud-protect.net/email-details/?k=k1&payload=53616c7465645f5fed27a22a24a04d2b4474850fcd4085279f5deb0a4b45aff271dc217bd5b8ac8e65b868f686679b9d5ae69c216b8828c6ab976fd096f84ebdac1ecb38a6f62a2e05b1ce3cda3ef1fc6615c2d5d63b3db6ac3d93719e10964cf6ecb92b637712794fd9814a36d8e401e9510d22d52433dc8526a1fd76ffd29c927dd092a286a002fa6edad24fdc289956069ff246bd9f54272522f4c2b34608a52f7c8a6db9c157660efc922fcaa993a27ce11dcae209b3f911b99a3e50e92edf0e120af447100e9d80cd45918b2f85aa8673efb14e6bddb38cdfaa2e1ba5496bad5db8df0857d443aeb0399f46406f > > > Learn More< > https://godaddy1.cloud-protect.net/email-details/?k=k1&payload=53616c7465645f5fed27a22a24a04d2b4474850fcd4085279f5deb0a4b45aff271dc217bd5b8ac8e65b868f686679b9d5ae69c216b8828c6ab976fd096f84ebdac1ecb38a6f62a2e05b1ce3cda3ef1fc6615c2d5d63b3db6ac3d93719e10964cf6ecb92b637712794fd9814a36d8e401e9510d22d52433dc8526a1fd76ffd29c927dd092a286a002fa6edad24fdc289956069ff246bd9f54272522f4c2b34608a52f7c8a6db9c157660efc922fcaa993a27ce11dcae209b3f911b99a3e50e92edf0e120af447100e9d80cd45918b2f85aa8673efb14e6bddb38cdfaa2e1ba5496bad5db8df0857d443aeb0399f46406f > > > Potential Impersonation > The sender's identity could not be verified and someone may be > impersonating the sender. Take caution when interacting with this message. > > NkdkJdXPPEBannerEnd > > > > > 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.. > > > > > > --------------------------------------------------------------------- > > > To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org<mailto: > users-unsubscr...@tomcat.apache.org> > > > For additional commands, e-mail: users-h...@tomcat.apache.org<mailto: > users-h...@tomcat.apache.org> > > > > > > > > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org<mailto: > users-unsubscr...@tomcat.apache.org> > > For additional commands, e-mail: users-h...@tomcat.apache.org<mailto: > users-h...@tomcat.apache.org> > > >
