Moment of Inertia [ Hiran ]

Remains of a chair

I had earlier posted about, how I am responsible for breaking chairs in my office. Well, few days back, I was again bang on target. Well the chair was already broken, which I realized, when I sat on it. When Kumaresan, sat on it, it broke into pieces, making a loud noise. Well, since I was sitting on it earlier, I became the culprit.

the chair broke in an unrepairable condition. Look at these.

May the chair rest in peace.

Reading Binary Data in Ruby

Reading binary data is not that easy in Ruby. The `Pragmatic Programmers - Programming Ruby` guide, has documented `pack', `unpack' methods for `String' class, with which we can convert data (integer, float etc.) into binary format and vice-versa. But the problem was, everytime, I will have to refer the documentation, and see, things into details. In C/C++, assigning the data to a type specific pointer variable, and accessing the value, will do (which is so easy). In Java, they have made it more easier. `DataInputStream' class, defines specific methods for that.

Well, that was my inspiration. Moreover, referring the documentation for unpacking a binary stream, was like looking into logarithms. I came up with this.

Not a good piece of code, but it works, and is gone in production.

free page cache and dentries

I am using a large instance of EC2 (2 Dual Core AMD Opteron(tm) Processor 270, 7.5GB RAM), which is up since June 29th and showing availability of only 500MB of memory, in `top'. I had known the mathematics behind the RAM usage, that shows up in `top', but could not recollect.

Then, I thought that, since it had something to do with memory, why not look up `/proc/' entries. That's when I looked up the man page for `proc'. On detailed reading, I remembered the mathematics.

The used memory constitute of the `kernel buffers' and the `page cache'. See the output of `free'. Now my EC2 instance was showing almost 7GB memory used, out of which 5.5 GB was cached.

Now, I ran a small command on the shell:

echo 3 > /proc/sys/vm/drop_caches

Now, writing `3' to `/proc/sys/vm/drop_caches', clears the pagecache and dentries. To learn more, read manual page for `proc'.

When the cache was cleared, I had 6.5 GB of memory available. Usually, the cache is cleared by the Kernel, only on demand. So, if I run a program, which simply tries to use huge amount of memory, the Kernel, will clear the cache and make it available for the program to use.