Thursday, June 21, 2007

Snoop on Solaris and Ethereal

I am a big fan of Ethereal tool and use it frequently for analysis of network traffic.
The GUI is great and we can decode HTTP traffic from the TCP packet frames.

Recently I had to capture the traffic on a remote production box running on Solaris and did not have the time to install Ethereal there. I knew about the 'snoop' command on Solaris and had used it in the past to capture network calls.
But I did not know that the snoop command can write all captured network packets to a file that is RFC 1761- compliant. What that means is that I can write the packets to a file and then open that file anywhere in Ethereal :)

This was just what I needed for my scenario. Quick listing of snoop commands:

- To capture packets to a file and only those on port 9080
snoop -o fileName.cap port 9080

- To format a captured file in ASCII
snoop -i fileName.cap -x0

Time complexity and Space complexity of algorithms

I had just downloaded the SAP Memory Analyser and was impressed with its performance.
More information on this tool can be found here. Going thru their wiki, I read how they had taken pains to make critical operations have a time complexity of O(1).

Time complexity and Space complexity are terms used when dealing with algorithms. If the input size (problem size) for a algorithm increases, then how does it affect the time taken for the algorithm to complete and how how much more memory does it take?

If the time consumed by the algorithm is independant of the input size then the algorithm is said to be a complexity of O(1); i.e. a constant-time method. If the time taken is linear then it is known as linear-time method - O(n).

More information can be found at the following links:

Tuesday, June 05, 2007

Generating GUIDs on the client side web browser

If your application requires that a GUID be created to identify the client, then we have 2 options:

- If we are sure that the end users use only IE, then we can use the ActiveX function:
return new ActiveXObject("Scriptlet.TypeLib").
For other browsers, we can write a JS function as shown here.
Basically the function uses the random numbers and padding to generate a unique number.
Snippet of the JS function:
function generateGuid()
var result, i, j;
result = '';
for(j=0; j<32; j++)
if( j == 8 || j == 12|| j == 16|| j == 20)
result = result + '-';
i = Math.floor(Math.random()*16).
result = result + i;
return result

Friday, June 01, 2007

4 GB memory limitation for 32 bit machines

What is the maximum heap size that U can allocate to a JVM or a .NET runtime?
The answer is dependant on the operating system and hardware. On a 32-bit machine, the CPU can use only 32 bits to refer to a memory pointer. Hence 2^32 = 4 gb.

Out of this, 2gb is reserved for the kernel and 2 gb for the applications. Hence we can allocate only 2gb memory to an application. More info on this can be found here.

For a JVM, if we need to allocate more than 2 gb of heap, then we need to install the 64 bit version of the JDK. Also on a solaris box, start the java process with the -d64 option.