I have been struggling with a problem in Google App Engine, using Java, for several days.
Many times (about 50% of the time) when I try to request the connection to a Cloud Sql instance, the connection returns a null value, resulting in several NullPointerException messages when trying to invoke Cloud Sql queries (when invoking .prepareCall(stored_proc)).
I have the latest App Engine Java SDK, in a project service, shared with other services built in Python which consume this Java backend.
Could it be possible that after certain time the instance/s could crash (I am just testing at this point, so I am using default scalation)?
This is the code that returns null:
Class.forName("com.mysql.jdbc.GoogleDriver");
url = "jdbc:google:mysql://project:instance/database?user=root";
log.info(url);
return DriverManager.getConnection(url);
This is part of my configuration file:
<application>app</application>
<module>mod</module>
<version>1</version>
<threadsafe>true</threadsafe>
<use-google-connector-j>true</use-google-connector-j>
I tried several suggestions from other posts, but with no success at all.
Any suggestion will be welcome, thanks in advance.
I was facing the same problem while using Google Cloud SQL and App engine.
I solved the problem by managing the connection pool my self. I realised that when you request a new connection for each request and close it on completion of the thread. The other requests would get back a null resulting to NullPointException.
I decided to do the following and it work for me for like 2 years now.
Open a connection and keep it to a static class that has a number of connections;
Every time i want to find a connection to the database, i would first check if the is an available connection for me to use.
Incase a Query killed the connection, thus means i needed to request another extra connection just to for the sack of connection drops.
I will add this as an answer, since it is not exactly what Chrispinus mentioned, although he gave me a good idea for teh solution.
I went deeper in the code and found that some of the methods were not closing the database connection. I had assumed all of them were doing that, but looking at each method, I found I was wrong.
So, although it sounds obvious, check connections are being closed (or managed, as Chrispinus says) properly.
Related
I have been developing Standard Logic Apps with SQL Server successfully for some time, but suddenly can no longer connect. I'm using Azure AD Integrated as my Authentication Type, which I know is OK as I use the same credentials in SSMS. If I try to create a new credential, it is apparently successful but on save the Logic App says "The API connection reference XXX is missing or not valid". Something has changed, but I don't know what ... help!
per above, this was submitted to M/S and has been resolved as follows: the root cause is if a Logic App Parameter name includes an embedded space the problem with SQL connections is triggered. This is a pernicious problem, as the error message is quite unrelated to the root cause. Further, since embedded spaces are supported in Logic Apps e.g. in Step Names, it is easy to assume the same applies across the board.
The specific action we are trying to performe is to create a charge request with Stripe:
Charge charge = Charge.create(params);
Using Stripe's Java implementation (version 5.35.1) we encounter a APIConnectionException when running the application on the deployed App Engine server. Interestingly, the issue does not occur using App Engine's local dev server.
We contacted Stripe and they said everything is fine on their side. They explained that "this error indicates that your server is not able to contact our API and that it ends up timing out waiting for an answer. Usually, this is due to something misconfigured on your server such as a DNS not redirecting to Stripe properly."
We were wondering if there are some configuration settings on App Engine which cause the problem. However, since there is no specific error message we cound not figure out what might cause the connection problem.
Similar problems which did not provide enough help to resolve this issue: https://issuetracker.google.com/35901039
Thanks for your help!
The problem seems to have solved itself. It occured for a couple of days and since a few hours the exact same code is working fine. Just like in https://issuetracker.google.com/issues/35901039 the problem is suddenly gone for some reason.
When running my PHPUnit tests, I get the following error
PDOException: SQLSTATE[08004] [1040] Too many connections
I am running a lot of tests, but I am afraid this could happen in a not-test situation as well.
My tests are doing guzzle requests to my Lumen 5.2 API. The Lumen API basically gets a request and checks the oAuth token (connecting to the oAuth DB). If it is correct it connects to a different database (this is done by setting the $connection variable in the Model) and uses the Model to retrieve data.
Is the model not closing the connection?
Any idea? Is there any information I should provide, to help solve this problem?
I think it was actually due to PHPUnit being one huge script. Apparently Laravel/Lumen disconnects when the script finishes, but all testscases seem to count as one script. Adding \DB::disconnect(); in the tearDown solved my issue.
I'm trying to add timeouts to GWT sessions, by using the following code to check if a session is alive:
public boolean isSessionAlive() {
return System.currentTimeMillis() - getThreadLocalRequest().getSession()
.getLastAccessedTime() < timeout;
}
I based this code on many examples I saw on web for GWT sessions, such as this.
The above code works great while running on a local web server, but after deploying the project to App Engine it doesn't. The following always returns 0 on App Engine:
getThreadLocalRequest().getSession().getLastAccessedTime()
As far as I understand, the last accessed time is updated on each RPC call.
I made several calls, but this value still remains zero and incorrect result is returned.
Does anybody know how to fix this issue?
Things will change after deployed on GAE
Just today attended the session on app engine by #roman irani .
remember that App Engine is a distributed architecture so a difference from Java EE is that you are never guaranteed the same application server instance during request processing as the previous request. While the object is being serialized correctly in memcache, you still have to call setAttribute() every time due to the fact that memory is not shared.
Clear cut picture here to handle the session
I have found a workaround. Adding the following code in war/WEB-INF/web.xml will cause the session to expire after 30 minutes:
<!-- timeout in minutes -->
<session-config>
<session-timeout>30</session-timeout>
</session-config>
Reference: Session Timeouts with GWT RPC calls.
I got an assignment to do and for that I could use any www technology like HTML, JavaScript, PHP etc. I'm really sorry to say that I haven't studied any of these technologies. Therefore I took few tutorials and skimmed through them searching for answers.
I found solutions for many problems but one problem yet unsolved. It is this:
I want two clients to communicate through a server for this assignment. One send a message, server processes it and forwards it to the next.
None of PHP tutorials showed me anyway of doing this. All of them talked of communication between one client with a server.
Please help. Show me a way to do this. Thanks.
Currently, without reverting to cutting-edge (and possibly hacky/unreliable) techniques, your PHP server cannot initiate communications with a page you've already loaded into a web browser. This is a result of the way the HTTP protocol works.
One way to solve this would be polling on the "receiving" end for data. Something like a publish-subscribe pattern.
One way to do this would be:
One client sends data to the server using an HTTP request (XHR aka AJAX) specifying the target for this data (the other client).
The server stores this data in a persistent storage (local file, database, etc).
The second client periodically sends a request to the server asking if there's any new data for it to consume. This can be done using setInterval and XHR in JavaScript.
I would suggest you take a look at:
http://en.wikipedia.org/wiki/Publish/subscribe
And also, for a cutting edge way to do this, check out Socket.IO:
http://socket.io
You might want to Google on "php chat server." Building a chat server is a simple way to get started.
http://net.tutsplus.com/tutorials/javascript-ajax/how-to-create-a-simple-web-based-chat-application/
http://code.jenseng.com/jenChat/