Lifescaler

Smart trick to check some bottlenecks in your DB

Bogdan — Tue, 07 Oct 2008 09:20:52 +0000

There’s a nice tool called iostat to check the HDD related info, like number of reads/writes, amount of data processed, etc. It’s a must have for any good sysadmin, as it allows you to identify some of the bottlenecks in the DB.

Together with the vmstat tool - allows a user to see statistics for the virtual memory usage - form a powerful duo to use, especially when your DB is running very slow, but the processors are not fully used.

The tools have enough explanations on the man pages.

So, the only thing remaining is to start them up:

Open 2 terminal windows. The first one would run something like iostat -dx 10 (will display the device extended report, refreshed every 10 seconds - you can increase/decrease this number to suite your needs - too small is not very good, as it’s better to have stats over a longer period). The second one should run vmstat 10.

Last but not least, to get them you need to install the sysstat package (vmstat is in the procps package, installed by default). For ubuntu, type: sudo apt-get install sysstat.

Database sharding unraveled - part III

Bogdan — Mon, 16 Jun 2008 16:56:24 +0000

Before continuing, please read the first parts of the database sharding adventure:
Database sharding unraveled - part I
Database sharding unraveled - part II

Chapter 1. The small guys

Before really diving into high scalability principles, I want to take a moment to talk about why database sharding has an important role even in small startups or medium sized web-sites (5 - 30k unique visitors/day).

It is equally important and benefic for a smaller web business to prepare itself from the beginning to tackle large amounts of users cheap. If it’s not obvious enough, think about what happens to a web-page that gets some plain old Digg attention. The server quickly collapses and the user experience immediately turns from positive to mega negative.
As I’ve explained before, the whole purpose of sharding is to be able to use an unlimited number of cheap machines topped by an open-source database. As experience taught me, the web server will rarely die. Instead, the DB server will choke easily when having to deal with many simultaneous connections.
The database doesn’t even have to be very big.

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Cool trick to extract only what you need using regular expressions

Bogdan — Thu, 29 May 2008 08:22:14 +0000

I have a lot of article drafts sitting unused in my WP DB and I’ve decided to release them even though I don’t have very much time to get into details.
Here’s one of them.
I always comment the code I write like:

// Bogdan -> initializing dispatcher
$this->dispatcher->init();
//-

Very often I’m required to extract the parts of the code I wrote, even though they are not full functions or classes, but just simple variables, or…

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Symfony quickies 1

Bogdan — Sat, 24 May 2008 13:31:48 +0000

When issuing symfony-propel-build-model and using sfGuardPlugin, some errors might appear.
Error: Attempt to set foreign key to nonexistent table, sf_guard_user!

Solution: The solution is very simple and involves changing the name of the database in the schema.xml to propel. Don’t worry, the database name will remain the one set in propel.ini, this is just to leverage the different xml files so that foreign keys can be processed.
The whole line should be:

If that doesn’t work, try changing the package from lib.model to plugins.sfGuardPlugin.lib.model (not recommended but if it does the work, why not…;)).

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Is SEO going to die?

Bogdan — Wed, 21 May 2008 15:27:38 +0000

These days there’s a lot of talk about the slow but steady decrease in importance of the whole SEO phenomenon in the search engine world. So, the question on everyone’s lips is: Is SEO going to die?
The answer, no.
The discussion must first start with spam, because that’s the main reason why something needed to change. Search engines play a key role in a site’s traffic and that implies that Google’s or Yahoo’s or …’s job is to continuously try to give the user the best results possible. The strategy they were relying on was to measure the number of links and also the quantity and quality of keywords, but all these can be easily faked. There are tons of Black-Hat techniques out there (if you’re really looking for hardcore dummy content, checkout website generators and stuff like that), but that’s beyond the purpose of this analysis.

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IE Object required error and other common coding mistakes

Bogdan — Wed, 07 May 2008 13:38:53 +0000

Been having a lot of work on customizing Dokeos for a client, so didn’t really have any spare time to write. This post is about common mistakes or overlooks when developing RIAs with JavaScript.
First of all, something to always keep in mind when working with Internet Explorer: it will never ever act like you wish from the first time.

Pay extra attention especially when dealing with DOM elements, as it tends to throw errors that FF doesn’t - I’m not talking about the fact that IE is not DOM compliant and methods that work in Mozilla family browsers don’t exist in IE or have different names.
Here’s a list of things to remember:

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Simulating mouse clicks in JavaScript

Bogdan — Tue, 22 Apr 2008 10:10:22 +0000

There might be times when you would like to simulate a mouse click on an DOM Node and don’t know how (for instance, submitting a form when in multi-frame environment).
Furthermore, it would be nice if the functionality could extend the DOM, so as to be able to use it combined with other pre-existing features.
Here’s the script bellow, just added and use it as you please (Ex. document.getElementById(”my_element”).click();)

HTMLElement.prototype.click = function() {
var evt = this.ownerDocument.createEvent('MouseEvents');
evt.initMouseEvent('click', true, true, this.ownerDocument.defaultView, 1, 0, 0, 0, 0, false, false, false, false, 0, null);
this.dispatchEvent(evt);
}
}

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Flex Camp Bucharest 2008

Bogdan — Thu, 17 Apr 2008 22:40:19 +0000

On Thursday I’ve attended the Flex Camp in Bucharest. It was mainly for showcasing the latest release. I’m just going to quickly go through some pros and cons, as I owe them for the cool t-shirt.
Pros:

the tremendous work the Romanian team put into the flex builder; only someone who has worked on something like that knows the complexity of such a project
the nice location
the good educational talks about building RIAs
the passionate speakers

Cons

I really disliked the sense of superiority in the atmosphere, both from most of the Adobe team and from the audience. What they’ve accomplished in Romania is admittedly unique, but… Ehh,.. maybe it’s just me.

All in all it was a pleasant afternoon, so kudos to that!

The begining of the end for Second Life

Bogdan — Wed, 16 Apr 2008 17:37:12 +0000

I’ve been reading a very interesting post about why is second life a dead end. I guess I kind of knew it a while ago from now. The reason is very simple: it collapses under its own weight.
As hard as I try to envision a way in which it could rise from its ashes, I can’t. Every service in the internet-world will fail sooner or later if it gets to complicated. I’m sure you are wondering why is Second Life complicated. Well, it’s simply too big. I mean, I’ve setup an account, played around a little and soon got bored. It’s too big, too real-life like. I’ve got my own life, I don’t want another one. If you come up with something, you’d better at least try to make it different.
Over on the marketing side, the whole project started wrong. In order to be able to monetize your business, you must have the capacity to easily reach your target audience with some sort of publicity. Not only that, but you must also be able to concentrate your visitors in groups so that any form of commercial you send to them have maximum of efficiency. Only then is when people will pay.

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Database sharding unraveled - part II

Bogdan — Tue, 15 Apr 2008 21:22:04 +0000

After understanding how to pick the correct dividing logic we continue our journey into database sharding. Many say that sharding is partitioning and they are right, but keep in mind that it’s the most complex form of all. In order to better grasp the concept, think about a field of flowers. In a normal situation (database), the flowers are all together.

What if you want to pick only the red flowers? In this case you would have to check every flower and see which one has the desired color, than pick it up, but that would take to long.

Instead, why not plant all the flowers based on their color. So, if you’d like to get the red ones only, it would be easy as pie.
The only problem which could appear would be if you wanted only the flowers which had 5 petals. That is why you must carefully think things over before starting to split your data.

Alright then, we’ve setup the logic, what next? It’s time to implement it.Now, the implementation is the tricky part.

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