Nadav Samet's Blog » daily

Catching Up

thesamet — Thu, 19 Jul 2007 22:19:13 +0000

A lot has been going on lately:

1. I participated in an academic workshop in Vrnjačka Banja, Serbia.

2. More or less 20 hours after I returned from Serbia to Israel, I flew to Dublin, Ireland for a day of on-site interviews in Google.

3. I got married!

4. Few days before I got married, I’ve received a job offer from Google EU Headquarters in Dublin, Ireland. I’ll be relocating to Dublin in September!

Productivity Tip: Multitasking slows you down

thesamet — Wed, 11 Apr 2007 10:44:56 +0000

The picture says it all. Multitasking really slows you down. Suppose you have two tasks to do: Task A and Task B. When you perform your tasks alternately (as in the top line) you pay a big overhead cost. Each time you are resuming a task, you have to load all the information related to it into your head and to enter into the state of mind that you had been when you last stopped doing it. This overhead is known in computer science as context switch.

When you work on each task until it is done (bottom line), you save yourself the context switch overhead. And therefore you are able to finish earlier. Each of the tasks on the bottom line is completed before the corresponding task on the first row. By the deadline (finish time), you had completed both tasks and even had time to rest (the blue arrow).

I prefer to manage my work as in the second row. When I work on a software project, I always get into my working room knowing that I am on the task until it is done. After several minutes, my mind enters the world of the project I am doing. I can’t hear or see anything not related to it. I totally live it.

And before I notice, the task is done.

So why do people multitask?

Sometimes there is a need to show progress in two tasks. In that case, you can’t avoid switching between them. Sometimes you just can’t progress on a task until you get additional inputs on it and then it makes sense to switch to the other one.

Some people choose to multitask whenever one of the tasks becomes boring or they just don’t want to do it. It is like doing it in very small steps, where each step is bearable. But then, they spend on each and every step the overhead of switching to the task that they don’t enjoy doing. Quite weird, since with this strategy they end up spending more time on the things they don’t like. The solution is obvious. Allocate enough time and finish with the things you don’t enjoy doing at once!

WordPress MySQL Database Encoding Fun

thesamet — Sun, 08 Apr 2007 11:19:15 +0000

I’ve finished moving thesamet.com to a new web host. The most tedious thing to do was to move the WordPress SQL database to the new server.

It turns out that the database was created with latin1 character set while WordPress pushed utf8 encoded data to it. For those who got stuck in the same problem, here is what I did to transfer the data to a new server.

First, get a sql dump of your database. Use the encoding of the database when doing it (i.e. latin1). Here is how to do it from the command line:

$ mysqldump –default-character-set=latin1 -u db_user -p db_name > mydb.sql

After inspecting the dump, it turned out that this file could be considered as UTF8 encoded. this was to be expected as we had UTF8 data in the database considered as latin1 and we dumped it as latin1.

Python is known to have great support for handling Unicode, and is very comfortable to inspect strings with it. The next thing I did was to load the file with Python, and tried to decode the data as utf8.

>>> s = open(‘mydb.sql’).read()
>>> s.decode(‘utf8′)
Traceback (most recent call last):
File "", line 1, in
File "/usr/lib/python2.5/encodings/utf_8.py", line 16, in decode
return codecs.utf_8_decode(input, errors, True)
UnicodeDecodeError: utf8 codec can’t decode byte \x92 in position 561129: unexpected code byte

Great, so the first trouble comes at index 561129. Let’s see what’s in there:

>>> s[561110:561136]
‘ points of view, it\x92s good’

That \x92 looks suspicious. It turns out that this one is still encoded in latin1, and \x92 in unicode is some kind of ‘ (slanted single-quote or something). To translate it to UTF8, I did:

>>> ‘\x92′.decode(‘latin1′).encode(‘utf8′)
‘\xc2\x92′

Now changing all occurrences of \x92 to \xc2\x92, can change it in places we would not want. So before we do that, we check what the other occurrences of \x92 looks like:

>>> [s[i-5:i+5] for i,ch in enumerate(s) if ch==‘\x92′]
[‘\xd7\x9c\xd7\x95\xd7\x92… ‘, ‘w, it\x92s go’]

We see that the first occurrence of \x92 should not be changed, it is within a UTF8 string. So we are safe to do

>>> s=s.replace(‘it\x92s’, ‘it\xc2\x92s’)
>>> u8=s.decode(‘utf8′)

And this time the decoding succeeded. This means that our data contains valid UTF8. My case was easy, but you might have to repeat the above process several times until you get rid of all latin1 characters in your data. It might be possible that you’ll have latin1 data that looks like utf8, and you’ll need to do even more manual search/replace.

Now write the utf8-encoded string (s, not u8) to a new file:

>>> open(‘/tmp/out.sql’, ‘w’).write(s)

After that, I’ve changed all the CREATE statements in the SQL file from CHARSET=latin1 to CHARSET=latin1.

It is important to add SET NAMES=utf8; at the top of the file.

On the destination server I created the database with UTF8 default encoding:

CREATE DATABASE db_name DEFAULT CHARSET utf8;

and imported the new SQL file into the database:

mysql –default-character-set=utf8 -u db_user -p db_name < /tmp/out.sql

and voila, it works.

Another Way to Stop Bot Registrations

thesamet — Fri, 09 Mar 2007 09:49:51 +0000

Reported by Boris.

Back in December I’ve posted about the technique I use to stop spam on phpBB forums. The following enhancement of this idea appeared today on xkcd webcomic blog:

But it would not work, because even spambots cry at that.

Are You Paying For “Protection” On Your Blog?

thesamet — Thu, 08 Mar 2007 06:42:08 +0000

It is very common to hear stories in which criminals ask restaurant or shop owners to pay them money for the criminal’s “protection services”. Those who dare not to pay them, usually sorry for that few days after, when they find their business burning in flames.

Well, it seems that this phenomenon is now spreading in the blogosphere, as ShoeMoney, one of my favorite bloggers, received a letter asking him to pay protection money for protecting his Adsense income:

Subject: Alarm
From: “dragon dragon”
Date: Wed, March 7, 2007 1:05 pm
To: jeremy@shoemoney.com
————————————————————————–

This is a warning and if you don’t pay attention to it you will suffer from bad turns.
All your income is through Google Adsense and if you do not cooperate with us we will stop this income source. We would like you to pay us the total amount of USD 200 each month. This small amount could be considered as nothing compared to your earnings from Adsense. If you do not pay this amount we will have to close your account by the help of special robots and …! I am not happy to do this but I have to as there is no way out of it and I trust if you were me you would also have to do the same. I am an inventor and I have recently innovated a new design which will be accepted by scientific societies only if I can present a model in advance; and making the model takes money. They will register my new design only after they have checked all aspects of the same. My theory is changing the power into energy. If I succeed many big problems will be solved. All my design specification could be viewed in the following web log:

magnetic-machine.blogspot dot com

The magnets will be bought in installments and the amount you pay is to be paid monthly for the same. After the registration of my design, the entire amount which I received from you will be paid back.

If you collaborate with me, you have helped to the science. And if not, I will have to close your Google AdSense account. I seek your help for the sake of the Science and if you are not prepared to collaborate I will have to close your Google AdSense account

Oh well, at least he promises to pay the money back later.

Girlfriend Discovers a DoS Vulnerability in Gaim

thesamet — Thu, 22 Feb 2007 08:49:36 +0000

It will probably be hard for you to believe, but my girlfriend discovered a DoS vulnerability in Gaim. No, don’t worry. She is not a computer geek (One in a relationship is certainly enough). The story of my girlfriend’s important discovery goes like this:

I was chatting with her some days ago using Gaim (she uses MS Messenger). At some point, she had sent me the following attack vector:

:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(
:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(
:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(
:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(
:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(

As she deeply disliked something I had said to her …

Gaim replaced each “:(” with a sad animated emoticon. From a mysterious reason, a few dozens of sad emoticons made Gaim choke. CPU usage was at 100% and the system felt highly unresponsive. It was impossible to use Gaim at all.

Luckily, I was able to kill Gaim from the command-line. I started it again hoping for the best, however, when I opened the chat window again, the attack vector was still there (retrieved from the logs) and Gaim choked yet again. I had to manually remove the few last lines from the log files, so I’ll be able to speak with her again.

To make a long story short, my girlfriend is now happy again.

Note: This episode of Thesamet.com was recorded 10 days ago, when Gaim developers were notified of this.

Clarification: For some reason, some people consider this to be a chauvinistic post. My girlfriend is a very intelligent person, she is not interested in software security. We were both surprised that she unintentionally discovered this. That’s it.

P.S.: The first paragraph of this post was written by her. She said it will help it to “do well on digg”.

Strangest Hanukkah present from Google

thesamet — Sat, 23 Dec 2006 10:49:40 +0000

Sometimes Google does strange things.

I was told today that this blog shows up on the first page of search results for the term “בלוג” (which is blog spelled in Hebrew). Here is a screenshot for the lazy disbelievers (taken on December 23, 2006):

Hmm. I thought it should be hard to get on the front page of google for such a broad term. Especially, if you do nothing (intentionally, at least) to make it happen.

So at least for the time being, this blog receives tons of highly un-targeted traffic. Any ideas on how to monetize this?

The Curious Incident of the Chameleon in the Night-Time

thesamet — Thu, 21 Dec 2006 10:30:33 +0000

Ok. I’m usually not posting such stupid stuff. But I couldn’t hold myself this time.

I came into my bed room where I had this bed-linen with pictures of lizards, turtles, chameleons and other creatures. Then I saw something quickly moving from the sheet to the blanket. Looks like it came to life from the pictures. Amazing isn’t it?

(click on the picture for a larger version)