Topic: Apache 2.2 non-php memory leak

[dbnex14]

Hi Experts,

I am using Apache 2.2, mod_winnt, no php involved, no website. This is on Windows machine.

I am using a custom .so module acting as a server for number of devices (barcode scanners). Devices send request to this server, and this server talks to database.

Each device can send 4-8 requests to do something on database (insert, update, delete, query). There could be any number of device but already at around 10 devices, I start seeing constant memory increase and within 5-10 min, 2GB cap is reached. FastMM reports no memory leak.

I wrote a PowerShell script to stop httpd process and stop and start Apache service when memo reaches 1GB but that causes lots of restarts resulting in devices loosing connection.

Much appreciated,

[James Blond]

If you don't start and stop the windows service but restart apache by httpd -k restart it does a graceful restart on windows. See http://httpd.apache.org/docs/2.2/en/stopping.html#graceful

Of cause that is just a workaround. I guess you should check of you can change the code of your custom module and free the memory after allocating is not longer needed and or a request finished.

[dbnex14]

Hi James and thank you for the reply. To clarify, I am using FastMM to detect memory leaks. FastMM is not reporting any leaks, if I intentionally introduce one, I can see a leak being cought by FastMM. That tells me that Apache is not releasing memory to OS and this happens under certain circumstances only. If I have 1-2 devices only, then this issue is not happening. So, my guess is that it is caused by high number of requests sent to Apache.

Also, my PowerShell script is doing this to stop apache process and service and to start it (if memory has reached ca 0.8GB):

//below is PowerShell code
# If working set of httpd or httpd#1 is greather than threshold, stop and start
if($procobj.workingset -gt $Threshold)
{
# $ProcName is name of process reported by PowerShell (as httpd, httpd#1, httpd#2, ...)
echo $("Memory for " + $ProcName + " exceeds Threshold");

# Stop httpd process
stop-process -name $MyHTTPD -force

# Stop service $ServiceName (this is name of service in Windows->Services)
echo $("---> Stopping service: " + $ServiceName);
stop-Service $ServiceName;

# Start service $ServiceName (this is name of service in Windows->Services)
echo $("---> Starting service: " + $ServiceName);
start-Service $ServiceName;
}

As you can see, I am stopping httpd process, then stopping Apache service, then starting the service which will spawn new httpd process. Are you saying this is not good way of doing it?

Also, here are the Apache settings I am using:

#Commented out these 3
#KeepAlive On
#MaxKeepAliveRequests 0
#KeepAliveTimeout 3000

#these are in mod_mpm
# WinNT MPM
<IfModule mpm_winnt_module>
ThreadsPerChild 300
#MaxRequestsPerChild 0
MaxRequestsPerChild 50
#According to Apache documentation, if you get "An operation was
#attempted on something that is not a socket), you should use this to
#disable AcceptEx() WinSock v2 API. See:
# http://httpd.apache.org/docs/2.2/mod/mpm_winnt.html
Win32DisableAcceptEx
</IfModule>

I agree with you that recycling process should be temporary solution but right now, the problem is that I can not detect any leaks although Task Manager shows constant growth in memory. Anything you could suggest based on above?

btw, I dont know how to issue httpd -k from PowerShell

Much Appreciated,

[James Blond]

it is just the path to the binary.

Instead of
stop-process -name $MyHTTPD -force
and
stop-Service $ServiceName;
and
start-Service $ServiceName;

you do a one liner

[James Blond]

It doesn't necessarily that the memory leak go to the OS, but pumping up the httpd process.The winnt mpm has a number of threads.

[dbnex14]

[dbnex14]

[James Blond]

The docs are explaining it. Don't be fooled by the -k graceful. A restart under windows is always graceful.

http://httpd.apache.org/docs/2.2/en/stopping.html#graceful

if you still have a question please ask again.

[dbnex14]

[James Blond]

That last notice is ok. It is only a notice, not an error or a warning.
It is only because of the windows socket system. Apache was desinged to run under linux first and later came windows in the focus. You can get rid of that if you can upgrade to 2.4. Apache 2.2 is almost EOL.

Your module doesn't free the memory. That is for sure else the memory usage won't grow until there is no more memory left. I don't know your module, but it seems that at least the apache process doesn't leak. Since winnt mpm is using threads you can restart apache without killing the child process. It just creates new threads and kills the old ones.

[dbnex14]

And I do that by the command you posted earlier?

[James Blond]

Yes the -k restart does a graceful restart. On linux it is a bit different, but a restart on Windows is always graceful.

[dbnex14]

[James Blond]

Yes the max request thing does the same.

[dbnex14]