I think I never cared about these – but the way David Baron from Mozilla describes these, I think I will now.
The points he was making started seeming so crucial that I jotted them down as if taking notes – something I never did with previous videos.

The things which I picked up from this video are…

From fetching the DOM over the wire to displaying it, following steps take place in order…
(1) Compute => (2) Compute Style => (3) Construct the DOM frame => (4) Layout => (5) Paint

The further Left (towards (1)) you push the browser’s rendering engine via your DOM/JS/CSS, the slower the browser would get.

Hence…

Use as specific CSS tags as possible. The more generic tag, the higher performance hit while searching the DOM. For example, a “#some-id {}” is way way faster than “body > div p {}” – as in the second tag, a larger portion of DOM is parsed to check which elements are affected by the selector. You push the browser to start from stage (2).

“:hover” style hits the browser pretty badly – as it pushes the browser back to stage (2). Coupled with the above mentioned CSS selectors problem, it can lead to real slow computation. Use it with CSS selectors which are very very specific in nature.

Programmatic scrolling of tags (some of which might have overflow property) via javascript – as that does not causes re-computation of style (stage 2). While if you do it with CSS magic, you push your browser back to stage (2).

Mozilla’s rendering tree, while building itself – does not takes any element with with CSS property “display:none” into account – it just skips it. So when this property is flipped, it triggers a full re-computation of the tree – which is expensive. However if we use the style “visibility:hidden” – the rendering tree picks up the related element while building itself. Hence when visibility is flipped, its much faster as there is no re-calculation of the rendering tree.

An old one – when javascripts are being downloaded, the browser stops itself from any other processing and waits for the script to download and execute (as script can modify the DOM anyhow it likes). During this time, the precious time is lost – which could have been used in downloading other content – like images, DOM, CSS, etc. Hence – keep the javascripts as further in the DOM as possible. Use caching is possible.

Learn more about speeding up your website at – Yahoo’s best practices (YSlow stuff) – some of which we regularly follow at AdoMado.com

Related posts:

1. OMG! Chrome-4.0 is nearly 59% and 76% faster than Firefox-3.7a1pre on my T61 (Ubuntu Jaunty) Okay, to start off – I really wanted Firefox to...
2. Getting around the dreaded Operation Aborted error in Internet Explorer with Ruby on Rails If you have ever experienced this… …you know how painful...

Related posts brought to you by Yet Another Related Posts Plugin.

NetBeans code modification suggestion

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.

Here is a great tip – after deploying which, I did felt the response time for cold startup and the UrlBar get better.

And here are the results…

-rw-r–r– 1 makuchaku makuchaku 7.0K 2009-07-05 11:37 content-prefs.sqlite [BEFORE]
-rw-r–r– 1 makuchaku makuchaku 7.0K 2009-07-23 00:30 content-prefs.sqlite [AFTER]

-rw-r–r– 1 makuchaku makuchaku 553K 2009-07-23 00:25 cookies.sqlite
-rw-r–r– 1 makuchaku makuchaku 376K 2009-07-23 00:30 cookies.sqlite

-rw-r–r– 1 makuchaku makuchaku 97K 2009-07-23 00:15 downloads.sqlite
-rw-r–r– 1 makuchaku makuchaku 4.0K 2009-07-23 00:30 downloads.sqlite

-rw-r–r– 1 makuchaku makuchaku 257K 2009-07-23 00:20 formhistory.sqlite
-rw-r–r– 1 makuchaku makuchaku 251K 2009-07-23 00:30 formhistory.sqlite

-rw-r–r– 1 makuchaku makuchaku 2.0K 2009-07-11 13:51 permissions.sqlite
-rw-r–r– 1 makuchaku makuchaku 2.0K 2009-07-23 00:30 permissions.sqlite

-rw-r–r– 1 makuchaku makuchaku 18M 2009-07-23 00:26 places.sqlite
-rw-r–r– 1 makuchaku makuchaku 12M 2009-07-23 00:30 places.sqlite

-rw-r–r– 1 makuchaku makuchaku 2.0K 2009-06-05 21:09 search.sqlite
-rw-r–r– 1 makuchaku makuchaku 2.0K 2009-07-23 00:30 search.sqlite

-rw-r–r– 1 makuchaku makuchaku 11K 2008-11-04 22:02 signons.sqlite
-rw-r–r– 1 makuchaku makuchaku 11K 2009-07-23 00:30 signons.sqlite

-rw-r–r– 1 makuchaku makuchaku 3.0K 2009-05-31 02:03 sqlinjectionDB.sqlite
-rw-r–r– 1 makuchaku makuchaku 3.0K 2009-07-23 00:30 sqlinjectionDB.sqlite

-rw-r–r– 1 makuchaku makuchaku 303K 2009-07-09 23:41 ubiquity_ann.sqlite
-rw-r–r– 1 makuchaku makuchaku 294K 2009-07-23 00:30 ubiquity_ann.sqlite

-rw-r–r– 1 makuchaku makuchaku 2.0K 2009-07-05 11:39 ubiquity_skin_memory.sqlite
-rw-r–r– 1 makuchaku makuchaku 2.0K 2009-07-23 00:30 ubiquity_skin_memory.sqlite

-rw-r–r– 1 makuchaku makuchaku 2.0K 2009-07-11 10:36 ubiquity_suggestion_memory.sqlite
-rw-r–r– 1 makuchaku makuchaku 2.0K 2009-07-23 00:30 ubiquity_suggestion_memory.sqlite

-rw-r–r– 1 makuchaku makuchaku 287K 2008-11-23 21:09 urlclassifier2.sqlite
-rw-r–r– 1 makuchaku makuchaku 142K 2009-07-23 00:30 urlclassifier2.sqlite

-rw-r–r– 1 makuchaku makuchaku 19M 2009-07-23 00:28 urlclassifier3.sqlite
-rw-r–r– 1 makuchaku makuchaku 19M 2009-07-23 00:30 urlclassifier3.sqlite

-rw-r–r– 1 makuchaku makuchaku 2.0K 2009-06-13 00:10 webappsstore.sqlite
-rw-r–r– 1 makuchaku makuchaku 2.0K 2009-07-23 00:30 webappsstore.sqlite

I did not measure the cold startup time before and after the changes, but I can certainly see ff coming up more fast now. Fast enough – to make me sit and write this blog entry in the middle of coding a rails app.

More explanation about SQLite’s VACUUM and REINDEX operations.

Enjoy

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.

As finding friends/partners is to Speed Dating, finding investors/future-employees is to Startup Lunch.

Startup Lunch is an initiative on the lines of (and by) Proto.in and in concept, is very similar to speed dating.

The startup founders are seated on one side and the candidates get to say hello and have a quick conversation to talk about what the background of the founder is, why he started the company and what sort of person he is looking for, while asking questions to the candidate about the reason to join a startup and what his/her passions are and ten minutes later the same process continues with the next founder. Within an hour, you would have met/spoken to most of the startups, and by the end of the day would know whom to get in touch with for your first/next job.

The event, at present is organized across India – in Bangalore, Chennai, Mumbai, Delhi, Pune and Hyderabad.

Luckily, Pune’t meet has been clubbed with Open Coffee Club Meet. More details about the startup lunch are here

Its an unique opportunity for me – I’ve never met another budding entrepreneur in person – specially when he/she has a business plan in his/her hands. It would be awesome to see what all my peer fellas are upto. And specially important to see how ApnaBill.com is received amongst them.

Oh yes, I’ll be giving a short intro about ApnaBill.com at the Startup Lunch. More about it later…

Can’t really wait till Friday! Can you?

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.

Different scenarios which we thought could have been possible

• User A and User B both attack the same coupon at same time
• User B tries to lock a coupon which was previously locked by User A
• User A tries to lock multiple coupons at time – knowingly!
• User A accidentally locks multiple coupons at a time

More problems arise specially when you have no control over the payment gateway pages (ie. when you are using a redirect to a payment gateway).

• When does the timeout occurs
• What happens if a timeout occurs
• What if the transaction was _killed_ midway
• How to deal with timeouts and locking/unlocking mechanism, etc

The newest addition to ApnaBill.com code in the payment gateway interaction arsenal

Luckily, almost all problems were solved for ApnaBill – All we expect from the user is to follow what’s shown on screen. Even otherwise, he should be good! For everything else – as they say – is the dear support staff

Like that alert box? Try http://www.bioneural.net/2006/04/01/create-a-valid-css-alert-message/

Hmm, I think, we should profile all the user displayable messages before we launch. I want to make sure that all have the same tone.

PS: Me and Sandy have never brainstormed more on any other issue than concurrency handling.

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.

Keeping everything in mind together and working towards a solution is interesting. It made me think pretty nicely to come up with a solution which satisfies all scenarios (except the ones, over which I have no control).

Scenario

Your website X uses a Payment Gateway (PG). When a user Z initiates a transaction (Tx) – a Tx ID and amount value (minimalistic variables) are sent to the payment gateway. On the shopping cart side, the product which Z is buying, is locked inside the database so that some other user should not buy the same product. If the user makes a successful Tx with PG, your shopping cart is notified of the status & everyone is happy!

Problem Statement

Issues arise when the shopping cart is dependent on timeout values from the PG. There can be two worst cases in this scenario…

1. The user Z closes the browser (before completing the Tx) after he successfully opens the PG. By doing so, your shopping cart locks the product in your DB but is never able to unlock it back (because you will never receive a timeout communication from the PG) – until unless you run a separate thread or a cron job which keeps on freeing up locked products based on timeout value. If you have a large online store, doing 10000Tx simultaneously, this problem would lock 10000 of your products for the entire timeout value (in case an attacker launches an intelligent DoS on your store).
2. The user Z just keeps the browser window with PG open. A timeout has to occur before it is communicated back to the shopping cart.

Solution

Note – I have not yet implemented this in any of my products – this is just a theory!

In the first scenario, open up the payment gateway as a frame inside your website – with you controlling the top header like frame & the PG controlling the other frame. Further, create a constant pingback AJAX connection to your shopping cart through the top frame. Once the AJAX connection dies, you have an almost sure shot way of knowing that the browser is no more alive, or Z’s is no longer connected. Your cart logic can then take appropriate actions of unlocking your product. – This solves problem scenario 1

The second scenario is the worst of the worsts! Browser has not been closed, and the user Z can make the Tx anytime before PG expires his Tx. What we can try here is put up a javascript clock which keeps ticking like a timer – again, we can use our top frame as thats the only part that we control when a PG is displayed. This will keep informing the user about the urgency to finish the Tx. This timer can change colors from green to yellow to red, signifying increasing priority, etc. Moreover, on the server side – one can either have a separate thread/cron-job to unlock the locked products – or – before any new access is made to the locked up DB, the cart logic an check up which all Tx’s are in a stale state & free them up. This will surely slow down the system a bit, but this would almost render the DoS attack useless. That solves problem scenario 2.

This is just my maiden attempt at Payment Gateways. If you think, I can improve my idea, feel free to add your suggestions in the comments section.

ApnaBill.com would be definitely using some (if not all) of these concepts.

Related posts:

1. An interesting problem to solve when migrating wordpress blog to a new URL Problem Scenario I migrated my blog from makuchaku.info to makuchaku.in...

Related posts brought to you by Yet Another Related Posts Plugin.