A Twisted app I have was constantly getting killed due to memory problems. The program grew in size, consuming all of the system's memory before being shut down by the os. Restart and repeat.
This is on a virtual server, so I doubled the memory, and the issue resolved - the daemon stabilized at around 1.25GB of memory
Does anyone have advice on how I can best profile this to tell what/where all the memory is getting sucked up into ?
If info on the app helps, I'm using the twisted reactor and internet.timer.TimerService to poll a database for items to update through three 'services'. the items to process are pushed into a twisted.internet.defer.DeferredList , and their processing occurs in a deferToThread block. In the deferred process there are a handful of blocking operations ( fetching web pages, etc ) and a lot of HTML parsing ( beautiful soup and other libraries ). I've suggested the reactor.threadpool size to be 10 and each 'service' defers to thread using a SemaphoreService that has 10 tokens. I really expected this daemon to max out at around 400MB of memory, not 3x that.
This is more of a generic share of thoughts how I debug memory leak/usage problems in my twisted applications.
Twisted has a ssh server support, and is something which I add in to almost all of my projects in development.
The ssh provides a interactive python interpreter access to the method which has python garbage collector available and a number of helper functions which allow me to a) inspect count of the instances from a same class, b) start and stop inspection of changes of that count over time and c) to get all references of that class. The nice thing with the interactive interpreter is that it allows ad-hoc introspection of offending instances, their relation to other objects and the state of process they are in. This so far has always proven a valuable instrument to pinpoint exact location where I have forgot / unforseen the ref release problems in my projects.
Related
I am using Windows Azure SDK 2.2 and have created an Azure cloud service that uses an in-role cache.
I have 2 instances of the service running under normal conditions.
When the services scales (up to 3 instances, or back down to 2 instances), I get lots of DataCacheExceptions. These are often accompanied by Azure db connection failures from the process going in inside the cache. (If I don't find the entry I want in the cache, I get it from the db and put it into the cache. All standard stuff.)
I have implemented retry processes on the cache gets and puts, and use the ReliableSqlConnection object with a retry process for db connection using the Transient Fault Handling application block.
The retry process uses a fixed interval retrying every second for 5 tries.
The failures are typically;
Microsoft.ApplicationServer.Caching.DataCacheException: ErrorCode:SubStatus:There is a temporary failure. Please retry later
Any idea why the scaling might cause these exceptions?
Should I try a less aggressive retry policy?
Any help appreciated.
I have also noticed that I am getting a high percentage (> 70%) cache miss rate and when the system is struggling, there is high cpu utilisation (> 80%).
Well, I haven't been able to find out any reason for the errors I am seeing, but I have 'fixed' the problem, sort of!
When looking at the last few days processing stats, it is clear the high cpu usage corresponds with the cloud service having 'problems'. I have changed the service to use two medium instances instead of two small instances.
This seems to have solved the problem, and the service has been running quite happily, low cpu usage, low memory usage, no exceptions.
So, whilst still not discovering what the source of the problems were, I seem to have overcome them by providing a bigger environment for the service to run in.
--Late news!!! I noticed this morning that from about 06:30, the cpu usage started to climb, along with the time taken for the service to process as it should. Errors started appearing and I had to restart the service at 10:30 to get things back to 'normal'. Also, when restarting the service, the OnRoleRun process threw loads of DataCacheExceptions before it started running again, 45 minutes later.
Now all seems well again, and I will monitor for the next hours/days...
There seems to be no explanation for this, remote desktop to the instances show no exceptions in the event log, other logging is not showing application problems, so I am still stumped.
I have written a WCF service which is hosted as a windows service in a machine running windows server 2008 R2.
My problem is that within 24 hrs of operation the service starts consuming 100% cpu as seen in the task manager.
Now, I am trying to get to the bottom of this problem.
I have tried in vain:
Logging for errors in all loops(try,catch etc.) and service methods.
Reading Resource monitor from task manager.
Running performance monitor on my service.
Running database activity monitor in the Microsoft SQL server(to see if any locks are causing issues)
Neither of the approach has yielded a clear understanding of what is causing 100% cpu utilization.
Please show me a way in which I can debug this successfully.
Thanks in Advance !!!
I ran into this problem a bit last year with the web service basically behaving like it had a memory leak, slowly working it's way to 100% in memory and CPU usage.
One problem we found was that I was that each instance of my ServiceHost obj (one for each request) was using a common shared variable (db connection, I think) it borrowed from the executable program running my web service, which we have running as a Windows service. That shared variable prevented some of the memory from being released. Once we eliminated the shared variable, some of the memory and CPU problems went away.
The other thing we did was make the class used for our ServiceHost iDisposable so that we could put it into a Using statement, which theoretically should unload the object entirely from memory when End Using is hit.
So the combination of those two things made the difference for us, so hopefully, maybe it will work for you.
Another thing you might try is making your ServiceHost a singleton class, or changing your concurrencymode.
<ServiceBehavior(ConcurrencyMode:=ConcurrencyMode.Multiple,
InstanceContextMode:=InstanceContextMode.PerCall)>
In our case, we run multiple and instance our context percall, but you can change the settings and see if your problem goes away.
I implemented a web application to start the Tomcat service works very quickly, but spending hours and when more users are entering is getting slow (up to 15 users approx.).
Checking RAM usage statistics (20%), CPU (25%)
Server Features:
RAM 8GB
Processor i7
Windows Server 2008 64bit
Tomcat 7
MySql 5.0
Struts2
-Xms1024m
-Xmx1024m
PermGen = 1024
MaxPernGen = 1024
I do not use Web server, we publish directly on Tomcat.
Entering midnight slowness is still maintained (only 1 user online)
The solution I have is to restart the Tomcat service and response time is again excellent.
Is there anyone who has experienced this issue? Any clue would be appreciated.
Not enough details provided. Need more information :(
Use htop or top to find memory and CPU usage per process & per thread.
CPU
A constant 25% CPU usage in a 4 cores system can indicate that a single-core application/thread is running 100% CPU on the only core it is able to use.
Which application is eating the CPU ?
Memory
20% memory is ~1.6GB. It is a bit more than I expect for an idle server running only tomcat + mysql. The -Xms1024 tells tomcat to preallocate 1GB memory so that explains it.
Change tomcat settings to -Xms512 and -Xmx2048. Watch tomcat memory usage while you throw some users at it. If it keeps growing until it reaches 2GB... then freezes, that can indicate a memory leak.
Disk
Use df -h to check disk usage. A full partition can make the issues you are experiencing.
Filesystem Size Used Avail Usage% Mounted on
/cygdrive/c 149G 149G 414M 100% /
(If you just discovered in this example that my laptop is running out of space. You're doing it right :D)
Logs
Logs are awesome. Yet they have a bad habit to fill up the disk. Check logs disk usage. Are logs being written/erased/rotated properly when new users connect ? Does erasing logs fix the issue ? (copy them somewhere for future analysis before you erase them)
If not. Logs are STILL awesome. They have the good habit to help you track bugs. Check tomcat logs. You may want to set logging level to debug. What happens last when the website die ? Any useful error message ? Do user connections are still received and accepted by tomcat ?
Application
I suppose that the 25% CPU goes to tomcat (and not mysql). Tomcat doesn't fail by itself. The application running on it must be failing. Try removing the application from tomcat (you can eventually put an hello world instead). Can tomcat keep working overnight without your application ? It probably can, in which case the fault is on the application.
Enable full debug logging in your application and try to track the issue. Run it straight from eclipse in debug mode and throw users at it. Does it fail consistently in the same way ?
If yes, hit "pause" in the eclipse debugger and check what the application is doing. Look at the piece of code each thread is currently running + its call stack. Repeat that a few times. If there is a deadlock, an infinite loop, or similar, you can find it this way.
You will have found the issue by now if you are lucky. If not, you're unfortunate and it's a tricky bug that might be deep inside the application. That can get tricky to trace. Determination will lead to success. Good luck =)
For performance related issue, we need to follow the given rules:
You can equalize and emphasize the size of xms and xmx for effectiveness.
-Xms2048m
-Xmx2048m
You can also enable the PermGen to be garbage collected.
-XX:+UseConcMarkSweepGC -XX:+CMSPermGenSweepingEnabled -XX:+CMSClassUnloadingEnabled
If the page changes too frequently to make this option logical, try temporarily caching the dynamic content, so that it doesn't need to be regenerated over and over again. Any techniques you can use to cache work that's already been done instead of doing it again should be used - this is the key to achieving the best Tomcat performance.
If there any database related issue, then can follow sql query perfomance tuning
rotating the Catalina.out log file, without restarting Tomcat.
In details,There are two ways.
The first, which is more direct, is that you can rotate Catalina.out by adding a simple pipe to the log rotation tool of your choice in Catalina's startup shell script. This will look something like:
"$CATALINA_BASE"/logs/catalina.out WeaponOfChoice 2>&1 &
Simply replace "WeaponOfChoice" with your favorite log rotation tool.
The second way is less direct, but ultimately better. The best way to handle the rotation of Catalina.out is to make sure it never needs to rotate. Simply set the "swallowOutput" property to true for all Contexts in "server.xml".
This will route System.err and System.out to whatever Logging implementation you have configured, or JULI, if you haven't configured.
See more at: Tomcat Catalina Out
I experienced a very slow stock Tomcat dashboard on a clean Centos7 install and found the following cause and solution:
Slow start up times for Tomcat are often related to Java's
SecureRandom implementation. By default, it uses /dev/random as an
entropy source. This can be slow as it uses system events to gather
entropy (e.g. disk reads, key presses, etc). As the urandom manpage
states:
When the entropy pool is empty, reads from /dev/random will block until additional environmental noise is gathered.
Source: https://www.digitalocean.com/community/questions/tomcat-8-5-9-restart-is-really-slow-on-my-centos-7-2-droplet
Fix it by adding the following configuration option to your tomcat.conf or (preferred) a custom file into /tomcat/conf/conf.d/:
JAVA_OPTS="-Djava.security.egd=file:/dev/./urandom"
We encountered a similar problem, the cause was "catalina.out". It is the standard destination log file for "System.out" and "System.err". It's size kept on increasing thus slowing things down and ultimately tomcat crashed. This problem was solved by rotating "catalina.out". We were using redhat so we made a shell script to rotate "catalina.out".
Here are some links:-
Mulesoft article on catalina (also contains two methods of rotating):
Tomcat Catalina Introduction
If "catalina.out" is not the problem then try this instead:-
Mulesoft article on optimizing tomcat:
Tuning Tomcat Performance For Optimum Speed
We had a problem, which looks similar to yours. Tomcat was slow to respond, but access log showed just milliseconds for answer. The problem was streaming responses. One of our services returned real-time data that user could subscribe to. EPOLL were becoming bloated. Network requests couldn't get to the Tomcat. And whats more interesting, CPU was mostly idle (since no one could ask server to do anything) and acceptor/poller threads were sitting in WAIT, not RUNNING or IN_NATIVE.
At the time we just limited amount of such requests and everything became normal.
What is the best way to check memory usage in an ASP.NET MVC3 application?
I have been told by my hosting provider to recyle the IIS application pool every so often to improve the speed of the site. Is this what is 'recommended practice'? Surely I shouldn't need to restart my application every so often? I'd much rather find out if it is an issue with memory usage in my application and correct it. So any tips & best practices you use would be quite helpful too.
The application is based on ASP.NET MVC3, C# and EF Code First. Any guidance, links appreciated.
EDIT:
I found this page after I posted, which is quite useful. But I'd still like to hear any other views.
ASP.NET MVC and EF Code First Memory Usage
Thank you
I have a site that never recycles (until the machine is rebooted weekly)
Your application generally should keep performing fine. If it doesn't, there is some leak.
This can occur because
Cache never expires
Cache never expires
Session storage keeps growing and never times out
ObjectContexts are never disposed and kept in the session, etc
Objects that should be disposed aren't
Objects that are created via a dependency injection container aren't setup to release after each request, and thus potentially have internal collections that keep growing.
There are more causes - but these are a few main ones.
So the question really is 'there is no best practice - it depends on your app'
If you are worried about current sessions during a restart, keep in mind a restart can be quick and current requests are allowed to finish (sometimes) and forms authentication tokens will survive the restart, however sessions will not unless you configure an out of process state server.
If your memory usage keeps growing, then setup a restart schedule, otherwise do once a week or never - or setup once memory goes to XYZ then reset. ASP.NET will restart automatically once a certain threshold is reached as well based on what the hoster has setup on memoryLimit:
http://msdn.microsoft.com/en-us/library/7w2sway1.aspx
By default IIS recycles the application pool automatically at an interval (I think is 29 hours or so) but that is surely set by the host, no matter how little or how much memory you're the process is using. THe recycling trigger can be a time interval or when the process hits a certain memory usage limit. I'm sure any shared host has both of them set.
About memory usage, you can use the GC.GetTotalMemory method which will give you an approximate usage. Even when using Perfmon the readings aren't very accurate but it gives you an idea.
//global.asax.cs
void Application_EndRequest(object o,EventArgs a)
{
var ctype=Context.Response.Headers["Content-Type"];
if (ctype == null || !ctype.Contains("text/html")) return;
Context.Response.Write(string.format("<p>Memory usage: {0}</p>",GC.GetTotalMemory(false)));
}
Be aware that you'll see the usage increasing increasing until the GC kicks in and the usage will drop to a more 'realistic' value.
If you have the money I recommend a specialized tool such as the Memory profiler
Other things you can do to at least be ready if the application has memory or performance problems:
Proper layering of the application, means you can refactor the more inefficient parts without affecting the others.
The Repository pattern will be very helpful, because you can start using EF , find out that EF uses to much memory (like in the link you've found), but then you could switch the repository implementation to use PetaPoco or Dapper.net.
In general an OR\M is more of a heavy library, if the application doesn't need ORM features but just a quick way to work with a db, use from the beginning a mico-Orm like those mentioned above.
Always dispose objects implementing IDisposable.
When dealing with large db records, use pagination. It's good for both server resources usage and user experience
Apply the YAGNI (You Aint Gonna Need It) principle as much as possible, this somehow implies a bit of TDD :)
I'm working on a consumer web app that needs to do a long running background process that is tied to each customer request. By long running, I mean anywhere between 1 and 3 minutes.
Here is an example flow. The object/widget doesn't really matter.
Customer comes to the site and specifies object/widget they are looking for.
We search/clean/filter for widgets matching some initial criteria. <-- long running process
Customer further configures more detail about the widget they are looking for.
When the long running process is complete the customer is able to complete the last few steps before conversion.
Steps 3 and 4 aren't really important. I just mention them because we can buy some time while we are doing the long running process.
The environment we are working in is a LAMP stack-- currently using PHP. It doesn't seem like a good design to have the long running process take up an apache thread in mod_php (or fastcgi process). The apache layer of our app should be focused on serving up content and not data processing IMO.
A few questions:
Is our thinking right in that we should separate this "long running" part out of the apache/web app layer?
Is there a standard/typical way to break this out under Linux/Apache/MySQL/PHP (we're open to using a different language for the processing if appropriate)?
Any suggestions on how to go about breaking it out? E.g. do we create a deamon that churns through a FIFO queue?
Edit: Just to clarify, only about 1/4 of the long running process is database centric. We're working on optimizing that part. There is some work that we could potentially do, but we are limited in the amount we can do right now.
Thanks!
Consider providing the search results via AJAX from a web service instead of your application. Presumably you could offload this to another server and let you web application deal with the content as you desire.
Just curious: 1-3 minutes seems like a long time for a lookup query. Have you looked at indexes on the columns you are querying to improve the speed? Or do you need to do some algorithmic process -- perhaps you could perform some of this offline and prepopulate some common searches with hints?
As Jonnii suggested, you can start a child process to carry out background processing. However, this needs to be done with some care:
Make sure that any parameters passed through are escaped correctly
Ensure that more than one copy of the process does not run at once
If several copies of the process run, there's nothing stopping a (not even malicious, just impatient) user from hitting reload on the page which kicks it off, eventually starting so many copies that the machine runs out of ram and grinds to a halt.
So you can use a subprocess, but do it carefully, in a controlled manner, and test it properly.
Another option is to have a daemon permanently running waiting for requests, which processes them and then records the results somewhere (perhaps in a database)
This is the poor man's solution:
exec ("/usr/bin/php long_running_process.php > /dev/null &");
Alternatively you could:
Insert a row into your database with details of the background request, which a daemon can then read and process.
Write a message to a message queue which a daemon then read and processed.
Here's some discussion on the Java version of this problem.
See java: what are the best techniques for communicating with a batch server
Two important things you might do:
Switch to Java and use JMS.
Read up on JMS but use another queue manager. Unix named pipes, for instance, might be an acceptable implementation.
Java servlets can do background processing. You could do something similar to this technology in a web technology with threading support. I don't know about PHP though.
Not a complete answer but I would think using AJAX and passing the 2nd step to something thats faster then PHP (C, C++, C#) then a PHP function pick the results off of some stack most likely just a database.