Nguyen Tien Huy

Monday, December 16, 2013

handle close event of browser in flash

Tuning the network

Meticulous configuration of Nginx and Node.js would be futile without first understanding and optimising the transport mechanism over which traffic data is sent. Most commonly, NginX will be connected to your web clients and your upstream applications via TCP sockets.

Your system imposes a variety of thresholds and limits on TCP traffic, dictated by its kernel parameter configuration. The default settings are designed for accommodating generic networking use. They are not necessarily geared up for high-volumes of short-lived connections handled by a web server.

The parameters listed here are the main candidates for tuning TCP throughput of a server. To have these take effect, you can drop them in your /etc/sysctl.conf file, or a new config file such as /etc/sysctl.d/99-tuning.conf and run sysctl -p to have the kernel pick them up. We use a syctl-cookbook to do the hard work.

Please note the following values are guidelines, and you should be able to use them safely, but you are encouraged to research what each one means so you can choose a value appropriate for your workload, hardware and use-case.

net.ipv4.ip_local_port_range='1024 65000'
net.ipv4.tcp_tw_reuse='1'
net.ipv4.tcp_fin_timeout='15'
net.core.netdev_max_backlog='4096'
net.core.rmem_max='16777216'
net.core.somaxconn='4096'
net.core.wmem_max='16777216'
net.ipv4.tcp_max_syn_backlog='20480'
net.ipv4.tcp_max_tw_buckets='400000'
net.ipv4.tcp_no_metrics_save='1'
net.ipv4.tcp_rmem='4096 87380 16777216'
net.ipv4.tcp_syn_retries='2'
net.ipv4.tcp_synack_retries='2'
net.ipv4.tcp_wmem='4096 65536 16777216'
vm.min_free_kbytes='65536'

Higlighting a few of the important ones…

net.ipv4.ip_local_port_range

To serve a client request via an upstream application, NginX must open 2 TCP connections; one for the client, one for the connection to the upstream. If the server receives many connections, this can rapidly saturate the system’s available port capacity. The net.ipv4.ip_local_port_range directive increases the range to much larger than the default, so we have room for more allocated ports. If you’re seeing errors in your /var/log/syslog such as: “possible SYN flooding on port 80. Sending cookies” it might mean the system can’t find an available port for the pending connection. Increasing the capacity will help alleviate this symptom.

net.ipv4.tcp_tw_reuse

When the server has to cycle through a high volume of TCP connections, it can build up a large number of connections in TIME_WAIT state. TIME_WAIT means a connection is closed but the allocated resources are yet to be released. Setting this directive to 1 will tell the kernel to try to recycle the allocation for a new connection when safe to do so. This is cheaper than setting up a new connection from scratch.

net.ipv4.tcp_fin_timeout

The minimum number of seconds that must elapse before a connection in TIME_WAIT state can be recycled. Lowering this value will mean allocations will be recycled faster.

How to check connection status

Using netstat:

netstat -tan | awk '{print $6}' | sort | uniq -c

Using ss:

ss -s

https://engineering.gosquared.com/optimising-nginx-node-js-and-networking-for-heavy-workloads

http://www.cyberciti.biz/files/linux-kernel/Documentation/networking/ip-sysctl.txt

http://www.cyberciti.biz/faq/linux-tcp-tuning/

How to fix the "LANGUAGE = (unset)" perl errors on Debian

First try two commands:

$export LC_ALL=C.UTF-8

$sudo update-locale

If it does not work try:

Add two lines into /etc/environment file

$vi /etc/enviroment

LANG=en_US.UTF-8

LC_ALL=en_US.UTF-8

If it does not work try:

Posting this because I couldn't find a solution posted for a non-interactive way to fix this ...

THE PROBLEM: Perl gives LANGUAGE = unset errors.

perl: warning: Setting locale failed. perl: warning: Please check that your locale settings: LANGUAGE = (unset), LC_ALL = (unset), LANG = "en_US.UTF-8" are supported and installed on your system. perl: warning: Falling back to the standard locale ("C"). locale: Cannot set LC_CTYPE to default locale: No such file

INTERACTIVELY FIX (debian):

# dpkg-reconfigure locales
(Select your language and hit "OK")

PROGRAMTICALLY FIX (debian):

# sed -i "s/^# en_US/en_US/" /etc/locale.gen # grep -v "^#" /etc/locale.gen en_US ISO-8859-1 en_US.ISO-8859-15 ISO-8859-15 en_US.UTF-8 UTF-8
#localedef -v -c -i en_US -f UTF-8 en_US.UTF-8 # /usr/sbin/locale-gen Generating locales (this might take a while)... en_US.ISO-8859-1... done en_US.ISO-8859-15... done en_US.UTF-8... done Generation complete. # update-locale LANG=en_US.UTF-8
===========================================================================
Answering myself: I've managed to solve the problem by adding

Code:

LANGUAGE = en_US.UTF-8
LC_ALL = en_US.UTF-8
LANG = en_US.UTF-8
LC_TYPE=en_US.UTF-8

to /etc/environment and rebooting.

If it does not work try:

add following to /etc/default/locate

LC_CTYPE=en_US.UTF-8

LC_ALL=en_US.UTF-8

LANG=en_US.UTF-8

run sudo dpkg-reconfigure locales

select locate en_US.UTF-8 in the "Locates to be generated" tab.

select en_US.UTF-8 in the "Default locate for the system environment" tab.

run sudo reboot

VC++ Error Link 2019: unresolved external symbol "declspec(dllimport) public: static char* edecl ..."

Set Properties->C/C++->Language->Treat wchar_t As Built-in Type = No(/Zc:wchar_t-)

Sunday, December 15, 2013

Unix Nohup: Run a Command or Shell-Script Even after You Logout

When you execute a Unix job in the background ( using &, bg command), and logout from the session, your process will get killed. You can avoid this using several methods — executing the job with nohup, or making it as batch job using at, batch or cron command.

This quick tip is for beginners. If you’ve been using nohup for a while, leave us a comment and tell us under what situations you use nohup.

In this quick tip, let us review how to make your process running even after you logout, using nohup.

Nohup stands for no hang up, which can be executed as shown below.

nohup syntax:

# nohup command-with-options &

http://linux.101hacks.com/unix/nohup-command/

Wednesday, May 30, 2007

Processing a BufferedImage

To convert a color image to grayscale, you can use ColorConvertOp as follows:

import java.awt.image.*;
import java.awt.color.*;

ColorConvertOp op = new ColorConvertOp(ColorSpace.getInstance(CS_GRAY), null);
BufferedImage grayImage = op.filter(sourceImage, null);

To invert the colors in an image (producing a photographic negative effect), you might use a RescaleOp as follows:

RescaleOp op = new RescaleOp(-1.0f, 255f, null);
BufferedImage negative = op.filter(sourceImage, null);

To brighten an image, you can use a RescaleOp to linearly increase the intensity of each color value. More realistic brightening effects require a nonlinear transform, however. For example, you can use a LookupOp to handle brightening based on the square-root function, which boosts midrange colors more than colors that are dark or bright:

byte[] data = new byte[256];
for(int i = 0; i < 256; i++)
 data[i] = (byte)(Math.sqrt((float)i/255.0) * 255);
ByteLookupTable table = new ByteLookupTable(0, data);
LookupOp op = new LookupOp(table, null);
BufferedImage brighterImage = op.filter(sourceImage, null);

You can blur an image using a ConvolveOp. When processing an image by convolution, a pixel value in the destination image is computed from the corresponding pixel value in the source image and the pixels that surround that pixel. A matrix of numbers known as the kernel is used to specify the contribution of each source pixel to the destination pixel. To perform a simple blurring operation, you might use a kernel like this to specify that the destination pixel is the average of the source pixel and the eight pixels that surround that source pixel:

0.1111  0.1111  0.1111
0.1111  0.1111  0.1111
0.1111  0.1111  0.1111

Note that the sum of the values in this kernel is 1.0, which means that the destination image has the same brightness as the source image. To perform a simple blur, use code like this:

Kernel k = new Kernel(3, 3, new float[] { .1111f, .1111f, .1111f,
                                         .1111f, .1111f, .1111f,
                                         .1111f, .1111f, .1111f });
ConvolveOp op = new ConvolveOp(k);
BufferedImage blurry = op.filter(sourceImage, null);