I am running a simple server app to receive uploads from a fine-uploader web client. It is based on the fine-uploader Java example and is running in Tomcat6 with Apache sitting in front of it and using ProxyPass to route the requests. I am running into an occasional problem where the upload gets to 100% but ultimately fails. In the server logs, as well as on the client, I can see that Apache is timing out on the proxy with a 502 error.
After trying and seeing this myself, I realized the problem occurs with really large files. The Java server app was taking longer than 30 seconds to reassemble the chunks into a single file and so Apache would kill the connection and stop waiting. I have increased Apache Timeout to 300 seconds which should largely correct the problem but the potential remains.
Any ideas on other ways to handle this so that the connection between Apache and Tomcat is not killed while the app is assembling the chunks on the server? I am currently using 2 MB chunks and was thinking maybe I should use a larger chunk size. Perhaps with fewer chunks to assemble the server code could do it faster. I could test that but unless the speedup is dramatic it seems like the potential for problems remain and will just be waiting for a large enough upload to come along to trigger them.
It seems like you have two options:
Remove the timeout in Apache.
Delegate the chunk-combination effort to a separate thread, and return a response to the request as soon as possible.
With the latter approach, you will not be able to let Fine Uploader know if the chunk combination operation failed, but perhaps you can perform a few quick sanity checks before responding, such as determining if all chunks are accessible.
There's nothing Fine Uploader can do here, the issue is server side. After Fine Uploader sends the request, its job is done until your server responds.
As you mentioned, it may be reasonable to increase the chunk size or make other changes to speed up the chunk combination operation to lessen the chance of a timeout (if #1 or #2 above are not desirable).
Related
Is it possible that setting the IIS root to the same directory to the project root will cause a slow performance?
I have an ASP.NET Web Application that handles some SQL commands to GET/POST records on the local SQL database. Recently I have came up with an idea that I no longer have to start debugging each time to test the code by changing the root of IIS from the default (C:\inetpub\wwwroot) to the root of the web-application project folder.
However, after that, I have encountered a problem where some manipulation on the web GUI, especially which include POST requests get extremely slow. For example, adding a new document or rewriting an existing one on the database now take about a minute whereas they did less than 20 seconds. Also, it seems that repeating POST commands make themselves slower (restarting the computer reset the situation). So I guess some read/write process may leave garbage and it conflicts with other processes.
Could anyone suggest any core issue about this phenomenon? Also please let me kwno if my explanation isn't enough clear to show the problem.
I have encountered a problem where some manipulation >on the web GUI, especially which include POST requests >get extremely slow
Changing the root directory is very unlikely to cause this issue.Your application was already performing very slow(20 seconds also is slow).
So no phenomenon in my opinion,You have to debug your application to find out where the delay is.To find out the root cause,you can use any profiler like perfview or a tool like debugdiag.
In case of debugdiag,choose the second option in the above link to capture a memory dump.Once you have a memory dump,simply double click the dump file and debugdiag will do an automated analysis and tell you where the problem is in your application code. E.g it can tell you your DB call is taking time .If you are not able to find,please post the analysis result updated with the question
I am using CentOS 5 + Webmin and Apache server. Sometimes it happen that some Apache process leave open connection and it use 100%. That can increase load average for +1. If sometimes happen more then one, there is a problem with load average, it's increased for 1-2-3.
Is it possible to add automatically kill Apache PID if it use 100% ? Or if is live longer then some time?
After manually terminate that PID, everything is back to normal, I would just like to find automatically way to terminate it in case it happen.
You should use monit or some similar solution, that allows you to monitor a process and take an action when CPU or memory usage is above any threshold.
I am using CloudFront with mod_pagespeed running on the server.
When updating a CSS or flushing the cache I see problematic behavior, first refresh on the browser returns the original css (this is fine). When I refresh a second time I get the correct manipulated CSS file name but the content of the file from CloudFront is still the original and not the correct manipulated content.
Why would this happen?
Any idea how to fix this?
Update:
For some reason it just stopped happening... I don't know why.
SimonW, since your original post there has been a feature added to pagespeed (in March 2013 in version 1.2.24.1) to deal with this issue directly. The directive is enabled via the following:
Apache:
ModPagespeedRewriteDeadlinePerFlushMs deadline_value_in_milliseconds
Nginx:
pagespeed RewriteDeadlinePerFlushMs deadline_value_in_milliseconds;
The docs describe the directive as follows (emphasis mine):
When PageSpeed attempts to rewrite an uncached (or expired) resource
it will wait for up to 10ms per flush window (by default) for it to
finish and return the optimized resource if it's available. If it has
not completed within that time the original (unoptimized) resource is
returned and the optimizer is moved to the background for future
requests. The following directive can be applied to change the
deadline. Increasing this value will increase page latency, but might
reduce load time (for instance on a bandwidth-constrained link where
it's worth waiting for image compression to complete). Note that a
value less than or equal to zero will cause PageSpeed to wait
indefinitely.
So, if you specify a value of 0 for deadline_value_in_milliseconds you should always get the fully optimized page. I would caution that the latency can be high on this in some cases. I my case, I really wanted this behavior, even with the latency concern, because the content was to be cached on my CDN's edge servers and, thus, I wanted the most optimized version possible to be served to the CDN for caching.
This could happen if you have multiple backend servers and CloudFront is hitting a different one than the HTML request went through. In that case the resource was rewritten on the HTML server, but not on the other server. There is a short timeout and if the other server doesn't finish the rewrite in that time, it will just serve the original content with Cache-Control: private,max-age=300. It's possible CloudFront caches that for a little while (even though obviously it shouldn't), but then eventually re-requests the resource from your backend and gets the correctly rewritten version this time.
If the logs file like access.log or error.log gets very large, will the large-size problem impact the performance of Apache running or user accessing? From my understanding, Apache doesn't read entire logs into memory, but just make use of filehandle to write. Right? If so, I don't have to remove the logs manually every time when it's large enough except for the filesystem issue. Please help and correct me if I'm wrong. Or is there any Apache Log I/O issue I'm supposed to take care when running it?
Thx very much
Well, i totally agree with you. Per my understanding apache access the log files using handlers and just append the new message at the end of the file. That's way a huge log file will not make the difference when has to do with writing to the file. But may be if you want to access the file or open it with a kind of logging monitoring tool then the huge size will slowdown the process of reading the file.
So i would suggest you to use log rotation to have an overall better end result.
This suggestion is directly form the apche web site.
Log Rotation
On even a moderately busy server, the quantity of information stored in the log files is very large. The access log file typically grows 1 MB or more per 10,000 requests. It will consequently be necessary to periodically rotate the log files by moving or deleting the existing logs. This cannot be done while the server is running, because Apache will continue writing to the old log file as long as it holds the file open. Instead, the server must be restarted after the log files are moved or deleted so that it will open new log files.
From the Apache Software Foundation site
How does Apache (most popular version nowadays, i guess) handle a connection to a script when this script is already being executed for another connection?
My guess has always been - upon receipt of a request to a script, script's contents are copied-to-memory/compiled/executed, and IF during this process there's another request to this script - same things happen (assuming Apache does not lock the script file, and simply gives another share of memory/cpu for another compilation/memory-storage/execution)
Or is there a queuing/waiting mechanism involved?
Assuming this additional connection is afforded enough memory, cpu, and does not pass maximum connections setting.
The quickly (and easy) answer is every request is processes by a new process.
Apache listens in some port and for each request create a new process that handles that request. That means no shared memory.
Also take a look to processes with "ps" command, you will see one "http" process for each request.
Take a look here for more complex working: http://httpd.apache.org/docs/2.0/mod/worker.html
and look at google too :) http://docstore.mik.ua/orelly/weblinux2/apache/ch01_02.htm