Faster and More Responsive Desktop in Linux

Faster Linux Desktop - Changing the scheduling paradigm to increase responsiveness for desktop useage

Came across an interesting article about speeding up the desktop usage in linux by altering the threading and process scheduling algorithm.

More details can be found here : http://blogs.computerworld.com/17371/the_linux_desktop_may_soon_be_a_lot_faster

My question is would this change performance for servers that have no graphical user interface running IE xorg? It looks like it won't!

Postgres unable to start with shmget. SHMMAX too small

Error Starting PostgreSQL, Could not create shared memory segment errors

If you have a large PostgreSQL configuration that supports many concurrent requests, you may find yourself starting it as you have increased the shared_buffers parameter or max_connections parameter, and it fails to start.

The error message will say something like could not create shared memory segment, Failed system call was shmget. This error usually means that PostgreSQL's request for a shared memory segment exceeded your kernel's SHMMAX parameter. You can either reduce the request size or reconfigure the kernel with larger SHMMAX. SHMMAX too small.

Here is the exact error message I got:

debian-testing:~# /etc/init.d/postgresql-8.3 start
Starting PostgreSQL 8.3 database server: mainThe PostgreSQL server failed to start. Please check the log output: 2010-11-17 13:53:34 EST FATAL: could not create shared memory segment: Invalid argument 2010-11-17 13:53:34 EST DETAIL: Failed system call was shmget(key=5432001, size=147382272, 03600). 2010-11-17 13:53:34 EST HINT: This error usually means that PostgreSQL's request for a shared memory segment exceeded your kernel's SHMMAX parameter. You can either reduce the request size or reconfigure the kernel with larger SHMMAX. To reduce the request size (currently 147382272 bytes), reduce PostgreSQL's shared_buffers parameter (currently 16384) and/or its max_connections parameter (currently 503). If the request size is already small, it's possible that it is less than your kernel's SHMMIN parameter, in which case raising the request size or reconfiguring SHMMIN is called for. The PostgreSQL documentation contains more information about shared memory configuration. failed!
 failed!

PostgreSQL Debian increase SHMMAX

In order to increase the maximum amount of shared memory a linux program can access, we need to adjust kernel parameters. Since we are using Debian they are available in /etc/sysctl.conf. This should be similar for many linux distributions.

We simple edit this file:

sudo vim /etc/sysctl.conf

or if you have GNOME running

sudo gedit /etc/sysctl.conf

And either search for the line or add the line (most likely will have to add) :

kernel.shmmax = 147382272

Note the number here is the same as "size" in this system call, shown in my error message above: shmget(key=5432001, size=147382272, 03600)

Now we have to put these settings into effect by running the command

sysctl -p

And now we start PostgreSQL up without the error:

debian-testing:~# /etc/init.d/postgresql-8.3 start
Starting PostgreSQL 8.3 database server: main.
debian-testing:~#

Intel OpenCV Open Source Computer Vision Software

Face Tracking, Motion Tracking, OpenCV - Free Computer Vision Library

Was looking into how to do face tracking and possibly motion tracking. With face tracking I was hoping I could find a way to track facial expressions, ie the eyebrow position, mouth position, as is done with many CG characters nowadays. OpenCV is an open library by Intel that allows you to carry out various computer vision tasks. Facial tracking is one of the demos that comes with OpenCV.

How OpenCV's facial tracking works can be described in great detail

You can find out more about how OpenCV's facial tracking works here : http://www.cognotics.com/opencv/servo_2007_series/part_3/sidebar.html

Check out Intel's OpenCV library - computer vision

Check out the a wiki for more detailed information here : http://opencv.willowgarage.com/wiki/

Face Tracking OpenCV - Cool demo on youtube

http://www.youtube.com/watch?v=AUhFjG-WSPE

Mozilla's HTML 5 Audio API Draft

HTML 5 - Mozilla's Draft for the Audio API

Defining an Enhanced API for Audio (Draft Recommendation) by Mozilla

Was looking into writing a html 5 script that can generate tones given a frequency (ie 440 hz for 'A') . Alas, it seems out of my reach for now as Mozillas Audio Writing API does not appear to work in my version of firefox. Cmon people lets get moving!

https://wiki.mozilla.org/Audio_Data_API

Cool Examples

Toy Piano
Javascript text-to-speech engine

Let me know if any of these work for you, because they don' work for me :(

Site Launch

Sheet-Music-Tabs.com

New site has been launched. Lets watch the SEO value... lots of competition out there

Sheet-Music-Tabs.com

New! Speed of Flow tabs by The Rodeo Carburettor

Load Balancing Web Servers using ldirectord

Web Server Load Balancing

Summary

Using ldirectord to set up load balancing in apache, using debian linux as my distro, should also work on ubuntu or any other distro for that matter (bsd, red hat, etc). See below for links to the documentation. This setup is done using ldirectord's masq mode, which is basically ip masquerading function using iptables.

Let's Begin

Im just going to take a few mins to explain my load balancing set up. What we have is 1 router, the default gateway, connected to the internet, and also connecting to an internal network. Standard set up really.

What we want to do is set up load balancing with 2 (or more, our case we have 4) apache servers.

First step - download ldirectord

http://horms.net/projects/ldirectord/ (ldirectord) is a daemon that will route traffic to a certain host based on whatever load balancing algorithm you choose. Some examples of algorithms are round robin, where it selects the next host every time, or least connections, route to the host with the least number of open connections. There are a few other options that are covered in the ldirectord documentation (man page) and specifically for the algorithms is in the IPVSADM man page under -s (scheduler) located here (http://linux.die.net/man/8/ipvsadm)

Note that ldirectord is now a sub project of linux HA project called Heartbeat. It is available as a part of that package available here http://www.linux-ha.org/wiki/Main_Page

The reason for this is ldirectord is used as a part of that package. It is also useable on its own as I will show you.

Ldirectord set up

What we have to do next is set up ldirectord after we manage to get it compiled. Here is an example of a /etc/ha.d/ldirectord.cf:

# Global Directives
checktimeout=10
checkinterval=2
autoreload=no
logfile="local0"
quiescent=yes

# Virtual Server for HTTP
virtual=10.1.1.10:80
        real=10.1.1.21:80 masq
        real=10.1.1.22:80 masq
        real=10.1.1.23:80 masq
        real=10.1.1.12:80 masq
        service=http
        request="ldirectord.html"
        receive="Test Page"
        scheduler=wlc
        protocol=tcp
        checktype=negotiate

As you can see, we have set this ldirectord program up on the host located at 10.1.1.10 which is a physical machine. Using Heartbeat you can set up a virtual IP address and have 2 or more machines take over that address when the main one goes down, but that is for another article. We are strictly focusing on setting up ldirectord here.

Setting up the load balanced machines

On each of the load balanced machines (10.1.1.21, 22, 23, and 12) we need to set the default gateway to 10.1.1.10 (the ip address of the load balancer) Please adjust accordingly to your network. This can be done using the following command on debian linux and most other types

route add default gw 10.1.1.10

Next we have set up our ldirectord to check each machine by loading the page "ldirectord.html" shown above. So really it will be trying to access the page http://10.1.1.21/ldirectord.html. We have set up a regular expression as well above saying "Test Page". As long as this url returns this string somewhere, the host will be considered "up" by ldirectord. After we have set everything up, it should be good to go.

Running ldirectord

Please make sure your config file is in /etc/ha.d/ldirectord.cf because the script will be searching there for it. Next run ldirectord by typing

/usr/bin/perl /usr/sbin/ldirectord start

You should make a init.d script for this. After you have run ldirectord, typing

ipvsadm -L

should give you some information on its status.

s5:/etc/ha.d# ipvsadm -L
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  s5.np.local:www wlc
  -> s4.np.local:www              Masq    1      6          2245      
  -> s7.np.local:www              Masq    1      5          2275      
  -> s3.np.local:www              Masq    1      4          2563      
  -> s9.np.local:www              Masq    1      6          2074

Here it shows that all hosts are up (their "Weight" is each 1) and have active connections running to them.

Setting up external routing

Now just have your router point all web traffic to 10.1.1.10:80 and you should have full load balancing. Note there are other problems such as how are you going to make sure they are all synchronized. You can use tools such as rsync, or use NFS to mount a share that contains all your files on each of the slave servers (our approach). The NFS approach seems to work nicely, however if you are hosting webservers for file transfers it may become a bottleneck so make sure your internet network is fast (1000 mbit) and tweaking NFS settings to your liking.

Thank you, your comments are welcome!

Parsing Wavefront .obj using Python

Wavefront OBJ File Format Parsing in Python

I thought I would share some simple parsing information about the wavefront .OBJ file format using python. The thing I like about this format is that it is stored in plain text, and easy to use if you are writing simple 3D game engines, or just 3D modeling programs.

You can use this parser to load wavefront files using python, and possibly to view the wavefront obj file.

Overview of the wavefront .OBJ file format

Based on http://en.wikipedia.org/wiki/Obj

Basically, our approach is to go line by line through the file. If the line starts with a "v", we are dealing with a vertex. If the line starts with a "vt" then we are dealing with a texture coordinate (u, v, optionally w). "n" means normal. "f" means its a face index. These are a bit special, but not too difficult to grasp. Our exported models that are from blender will all have normal vectors, and texture coordinates (make sure you specify the texture coordinates in blender or there will be none). The "f" lines will look like this:

f v1/vt1/vn1 v2/vt2/vn2 v3/vt3/vn3

where "v1" is the vertex array index, "vt1" is the texture coordinate index, and "vn1" is the normals array index. This particular face is a triangle. I recommend storing triangles, and quads in 2 different arrays. They can both reference your vertex/texture coordinate/normals array.

Very important note before we begin

The index format in the .OBJ Wavefront file format is 1 based, not 0 based. Thus, we should subtract 1 from the actual number in order to get a 0 based index, and make it compatible with python lists or any array type.

#do the loading of the obj file
def load_obj(filename) :
 V = [] #vertex
 T = [] #texcoords
 N = [] #normals
 F = [] #face indexies

 fh = open(filename)
 for line in fh :
  if line[0] == '#' : continue
 
  line = line.strip().split(' ')
  if line[0] == 'v' : #vertex
   V.append(line[1:])
  elif line[0] == 'vt' : #tex-coord
   T.append(line[1:])
  elif line[0] == 'vn' : #normal vector
   N.append(line[1:])
  elif line[0] == 'f' : #face
   face = line[1:]
   if len(face) != 4 : 
    print line
    #raise Exception('not a quad!')
    continue
   for i in range(0, len(face)) :
    face[i] = face[i].split('/')
    # OBJ indexies are 1 based not 0 based hence the -1
    # convert indexies to integer
    for j in range(0, len(face[i])) : face[i][j] = int(face[i][j]) - 1
   F.append(face)

 return V, T, N, F

Please not this program will give you string representations. You should loop through these arrays again and convert them to the proper format (int, float, etc).

Please leave your comments