I am trying to build a web service on top of hbase, so the code looks roughly like:
#GET
#Path("/blabla")
#Override
public List<String> getEvents($$$params$$$) {
......
//calling hbase query the events
......
}
When Hbase service is down, the hbase Java API keeps retrying to connect to Hbase region server util eventually it times out and throws a RT Exception:
NoServerForRegionException: Unable to find region for event,,99999999999999 after 10 tries.
The logic has no problem, my issue here is that the HttpClient times out way before hbase times out the retries. Then my web service API consumer gets no response, ugly.
Question -
What's the best practice here if you have server's timeout potentially longer than the http connection itself? How to have the web service respond to client gracefully in this case?
set the cashing for you scan object to some reasonable value. another thing, since you are using a web service to show the results to your users, i am assuming that you must be showing only a few rows(or records) at a time. you can use Hbase PageFilter so that you get only a specified no of rows each time and don't have to wait to get all the rows in one shot.
Related
We have a Reactive REST API using Spring Data Neo4j (SpringBoot v2.7.5) deployed to Kubernetes. When running a stress test to determine the breaking point, once the volume of requests that the service can handle has been breached, the service does not auto-recover, even after the load has dropped to a level at which the service can handle.
After the service has fallen over the Neo4J health indicator shows:
“org.neo4j.driver.exceptions.ClientException: Unable to acquire connection from the pool within configured maximum time of 60000ms”
With respect to connection/configuration settings we are using defaults configured by SDN.
Observations:
Up until the point at which the service breaks only a small number of connections are utilised, at the point at which it breaks the connections in use jumps up to the max pool size and the above mentioned error is observed. No matter how much time passes (even well beyond the max connection lifetime) the service is unable to acquire a connection from the pool. Upon manually shutting down and restarting the service/pod the service returns to a healthy state.
As an interim solution we now check the Neo4J health indicator, if the mentioned error is present the liveness state is set to down which triggers Kubernetes to restart the service automatically. However, I’m wondering if there is an underlying issue with the connections in the pool not getting ‘cleaned up’?
You can take a look at this discussion https://github.com/spring-projects/spring-data-neo4j/issues/2632
I had the same issue. The problem is that either Spring Framework or Neo4j reactive transaction manager doesn't close connections in a complex reactive flow e.g. when there are a lot of inner calls/mappings and somewhere inside an exception is thrown.
So as a workaround you can add #Transactional in such places to avoid multiple transactions to be created.
We're developing warehouse app for picking items which sends requests to a web service on every item scan, e. g. to update the quantity scanned in DB. From the log files I saw thet every now and then the connection on android scanners is lost and that leads to item quantity not being updated or in worst case an app crash.
What would be the best way to handle such connection failures so that I can ensure that the call to web method was successul before continuing code execution? Should I define some variable which accepts response from the web method and repeat the call until success is returned? Or is there some smarter way?
I have a web service that is made using spring, hibernate and c3p0. I also have a service wide cache(which has the results of requests ever made to the service) which can be used to return results when the service isn't able to return(due to whatever reason). The cache might return stale results when the database is out but that's ok.
I recently faced a database outage and my service came to a crashing halt.
I want the clients of my service to survive database outages happening ever again in future.
For that, I need my service to:
Handle new incoming requests like this: quickly say that the database is down and throw some exception(fast-fail).
Requests already being processed: Don't last longer than x seconds. How do I make the thread handling the request be interrupted somehow.
Cache the whole database in memory for read-only purposes(Is this insane?).
There are some observations that I made:
If there is one or more connection(s) with status ESTABLISHED, then an attempt to checkout a new connection is not made. Seems like any one connection with status ESTABLISED is handed over to the thread receiving the request. Now, this thread just hangs till the time the database comes back up.
I would want to make this request fast-fail by knowing before handling over a connection to a thread whether db is up or not. If no, the service should throw exception instead of hanging up.
If there's no connection with status ESTABLISHED, then the request fails in 10 secs with the exception that "Could not checkout a new connection". This is due to my checkout timeout being set for 10s.
If the service was processing some request, now the db goes and then the service makes a call to db, the thread making the call to db gets stuck forever. It resumes execution only after the db comes back.
I would like to interrupt the thread after say x seconds whether or not it was able to complete the request.
Are there ways to accomplish what I seek?
Thanks in advance.
I have a Java web app hosted on Google App Engine (GAE). The User clicks on a button and he gets a data table with 100 rows. At the bottom of the page, there is a "Make Web service calls" button. Clicking on that, the application will take one row at a time and make a third party web-service call using the URLConnection class. That part is working fine.
However, since there is a 60 second limit to the HttpRequest/Response cycle, all the 100 transactions don't go through as the timeout happens around row 50 or so.
How do I create a loop and send the Web service calls without the User having to click on the 'Make Webservice calls' more than once?
Is there a way to stop the loop before 60 seconds and then start again without committing the HttpResponse? (I don't want to use asynchronous Google backend).
Also, does GAE support file upload (to get the 100 rows from a file instead of a database)
Thank you.
Adding some code as per the comments:
URL url = new URL(urlString);
HttpURLConnection connection = (HttpURLConnection) url
.openConnection();
connection.setDoOutput(true);
connection.setRequestMethod("POST");
connection.setConnectTimeout(35000);
connection.setRequestProperty("Accept-Language", "en-US,en;q=0.5");
connection.setRequestProperty("Authorization", encodedCredentials);
// Send post request
DataOutputStream wr = new DataOutputStream(
connection.getOutputStream());
wr.writeBytes(submitRequest);
It all depends on what happens with the results of these calls.
If results are not returned to a UI, there is no need to block it. You can use Tasks API to create 100 tasks and return a response to a user. This will take a few seconds at most. The additional benefit is that you can make up to 10 calls in parallel by using tasks.
If results have to be returned to a user, you can still use up to 10 threads to process as many requests in parallel as possible. Hopefully, this will bring your time under 1 minute, but you cannot guarantee it since you depend on responses from third-party resources which maybe unavailable at the moment. You will have to implement your own retry mechanism.
Also note that users are not accustomed to waiting for several minutes for a website to respond. You may consider a different approach when a user is notified after the last request is processed without blocking your client code.
And yes, you can load data from files on App Engine.
Try using asynchronous urlfetch calls:
LinkedList<Future<HttpResponse>> futures;
// Start all the request
for (Url url : urls) {
HttpRequest request = new HttpRequest(url, HTTPMethod.POST);
request.setPayload(...)
futures.add(urlfetchservice.fetchAsync(request);
}
// Collect all the results
for (Future<HttpResponse> future : futures) {
HttpResponse response = future.get()
// Do something with future
}
I'm running an embedded jetty server (jetty 6.1.24) inside my application like this:
Handler handler=new AbstractHandler()
{
#Override
public void handle(String target, HttpServletRequest request,
HttpServletResponse response, int dispatch)
throws IOException, ServletException {
//this can take a long time
doSomething();
}
};
Server server = new Server(8080);
Connector connector = new org.mortbay.jetty.nio.SelectChannelConnector();
server.addConnector(connector);
server.setHandler(handler);
server.start();
I would like to set a timeout value (2 seconds) so that if handler.handle() method takes more than 2 seconds, jetty server will timeout and response to the client with 408 http code (request timeout).
This is to guarantee that my application will not hold the client request for a long time and always response within 2 seconds.
I did some research and tested it with "connector.setMaxIdleTime(2000);" but it doesn't work.
Take a look at the API for SelectChannelConnector (Jetty):
http://download.eclipse.org/jetty/7.6.17.v20150415/apidocs/org/eclipse/jetty/server/nio/SelectChannelConnector.html
I've tried to locate any timeout features of the channel (which controls incoming connections): setMaxIdleTime(), setLowResourceMaxIdleTime() and setSoLingerTime() are available it appears.
NOTE: the reason for your timeout feature not to work has to do with the nature of the socket on your operating system. Perhaps even the nature of Jetty (i've read about it somewhere, but cannot remember where it was).
NOTE2: i'm not sure why you try to limit the timeout, perhaps a better approach is limiting the buffer sizes? If you're trying to prevent denial of service...
Yes, this is possible. You could do this using DosFilter of Jetty. This filter is generally used to configure a DOS attack prevention mechanism for your Jetty web server. A property of this filter called 'MaxRequestMs' provides what you are looking for.
For more details, check this.
https://www.eclipse.org/jetty/javadoc/jetty-9/org/eclipse/jetty/servlets/DoSFilter.html