You can now subscribe to a tag (or set of tags) and get an email when new questions arrive.

To begin, visit the Tag Sets page on stackexchange.com, and either create a new tag set, or find a cool tag set someone else already put together.

Click on a tag set to browse the questions, then look on the sidebar for the email option:

Once you click subscribe, you can indicate which email address you want to use, and how often you want questions to be emailed to you — every 15 minutes, every 3 hours, or every day.

Once you click subscribe, you’ll automatically get emailed when new questions with those tags appear on any of our sites.

We already supported emailing new answers to questions you own, but we’ve intentionally avoided a lot of email notifications because, well, I hate email. That said, I do think interacting with our sites through email can make sense in some circumstances:

1. When you’re active in tags that are not getting a lot of regular activity, so there is never a steady stream of questions. Even if you visited the site all the time, you never know when the occasional new question will appear.
2. When you’re following one tag across multiple Stack Exchange sites, it can be simpler to have all the questions rolled up in an email summary rather than visiting many sites individually.
3. When you are an expert in a niche topic, but you don’t want to spend a lot of time browsing around related disciplines. You want to be notified when anything is going on in your specific area of interest, only.

Fundamentally it’s the classic divide between push (we notify you when there are new questions, at the risk of bugging you) and pull (you visit the site whenever you like and see for yourself if there are new questions, at the risk of missing some things). Of course, we still support RSS everywhere, as we always have.

We’re thinking of adding a simple one click “subscribe” option on the websites proper to make it easier to subscribe to a tag or set of tags. But until then, we’d like to gather data on what types of tag sets are getting actively used. So, as ever, visit the Tag Sets page, try it out, and let us know what you think!

One of the more popular Stack Exchange beta sites just came out of beta with a final public design:

programmers.stackexchange.com

Now watch closely as I read your mind.

I don’t get it! What’s the difference between Programmers and Stack Overflow?

I’m so glad you asked!

In a nutshell, Stack Overflow is for when you’re front of your compiler or editor working through code issues. Programmers is for when you’re in front of a whiteboard working through higher level conceptual programming issues. Hence the (awesome) whiteboard inspired design!

Stated another way, Stack Overflow questions almost all have actual source code in the questions or answers. It’s much rarer (though certainly OK) for a Programmers question to contain source code.

Remember, these are just guidelines, not hard and fast arbitrary rules; refer to the first few paragraphs of the FAQ if you want specifics about what Programmers is for:

Programmers – Stack Exchange is for expert programmers who are interested in subjective discussions on software development.

This can include topics such as:

• Software engineering
• Developer testing
• Developer tools and techniques
• Practical algorithms and data structures
• Design patterns
• Architecture
• Development methodologies
• Quality assurance
• Software law
• Code golf & programming puzzles
• Freelancing and business concerns

Although I fully supported this site when it was just a baby Area 51 site proposal, we’ve endured a lot of angst over it — mainly because it veered so heavily into the realm of the subjective. It forced us to think deeply about what makes a useful subjective question, which we formalized into a set of 6 guidelines in Good Subjective, Bad Subjective. Constructive subjective questions …

1. inspire answers that explain “why” and “how”.
2. tend to have long, not short, answers.
3. have a constructive, fair, and impartial tone.
4. invite sharing experiences over opinions.
5. insist that opinion be backed up with facts and references.
6. are more than just mindless social fun.

Ultimately, with a little extra discipline and moderation, I think the site turned out great. So, go forth and ask your subjective whiteboard questions on programmers.stackexchange.com! Just make sure they’re professional and constructive, please.

As we approach the end of the year, I thought I’d roll up some statistics that people occasionally ask about.

As a baseline — per Quantcast, the Stack Exchange Network is ranked #364 in overall USA network traffic, and Stack Overflow itself is ranked #598.

These numbers are from Google Analytics for the period of January 1, 2010 to December 14, 2010.

Where in the world do Stack Overflow users come from?

Compared to last year’s numbers, the trend here is basic globalization 101 — more and more traffic from outside the USA over time, where the US dropped from 36% to just 30% of the total in a single year. The top 10 countries only account for 66% of traffic overall, down from 71% last year.

How do Stack Overflow users find the site?

No, Google isn’t a monopoly, they just play one on the internet. Just kidding! please don’t hurt me mister googles

What web browsers do Stack Overflow users use?

Note that within Internet Explorer, the breakdown is 60% IE8, 26% IE7, and 13.5% IE6. The Firefox breakdown is primarily 3.5 and 3.6, with a smattering of older versions. Chrome is … all over the map, probably because by the time you read this, they’ve incremented the version again.

The big news here relative to last year is the huge jump for Chrome, mostly coming at the expense of IE and Firefox.

What operating systems do Stack Overflow users use?

We didn’t report these stats for last year, but I doubt they are terribly surprising to anyone.

What screen resolutions do Stack Overflow users have?

This is very good news compared to last year! What I mainly look at here is the horizontal width. We design for a fixed minimum width of 1024 px and that stat declined from 12% to 8% over the last year.

So there you have it — a profile of the average 2010 Stack Overflow user, at least for these metrics! I think this covers most of the questions I see asked on meta about our analytics, but if there are any other metrics you think might be useful to share, make a case for them in the comments.

Since we launched the Stack Exchange Data Explorer in June, we’ve been actively maintaining it and making small improvements to it. But there is one big change — as of today, the site has permanently moved from odata.stackexchange.com to

data.stackexchange.com

If you’re wondering what the heck this thing is, do read the introductory blog post, but in summary:

Stack Exchange Data Explorer is a web tool for sharing, querying, and analyzing the Creative Commons data from every website in the Stack Exchange network. It’s also useful as for learning SQL and sharing SQL queries as a ‘reference database’.

We are redirecting all old links to the new path, so everything should work as before. Why did we make this change?

Mostly because we decided to move off the Windows Azure platform. While Microsoft generously offered us free Azure hosting in exchange for odata support and a small “runs on Azure” logo in the footer, it ultimately did not offer the level of control that we needed. I’ll let Sam Saffron, the principal developer of SEDE, explain:

Teething issues

When we first started working with Azure, tooling was very rough. Tooling for Visual Studio and .NET 4.0 support only appeared a month after we started development. Remote access to Azure instances was only granted a few weeks ago together with the ability to run non-user processes.

There are still plenty of teething issues left, for example: on the SQL Azure side we can’t run cross database queries, add full-text indexes or backup our dbs using the BACKUP command. I am sure these will eventually be worked out. There’s also the 30 minute deploy cycle. Found a typo on the website? Correcting it is going to take 30 minutes, minimum.

Due to many of these teething issues, debugging problems with our Azure instances quickly became a nightmare. I spent days trying to work out why we were having uptime issues, which since have been mostly sorted.

It is important to note that these issues are by no means specific to Azure; similar teething issues affect other Platform-As-A-Service providers such as Google App Engine and Heroku. When you are using a PAAS you are giving up a lot of control to the service provider. The service provider chooses which applications you can run and imposes a series of restrictions.

The life cycle of a data dump

Whenever there is a new data dump, I would log on to my Rackspace instance, download the data dump, decompress it, rename a bunch of folders, run my database importer, and wait an hour for it to load. If there were any new sites, I would open up a SQL window and hack that into the DB. This process was time consuming and fairly tricky to automate. It could be automated, but it would require lots of work from our side.

Now that we migrated to servers we control, the process is almost simple — all we do is select a bunch of data from export views (containing public data) and insert them into a fresh DB. We are not stuck coordinating work between 4 machines across 3 different geographical locations.

Did I mention we are control freaks?

At Stack Overflow we take pride in our servers. We spend weeks tweaking our hardware and software to ensure we get the best performance and in turn you, the end user, get the most awesome experience.

It was disorienting moving to a platform where we had no idea what kind of hardware was running our app. Giving up control of basic tools and processes we use to tune our environment was extremely painful.

We thank Microsoft for letting us try out Azure; based on our experience, we’ve given them a bunch of hopefully constructive feedback. In the long run, we think a self-hosted solution will be much simpler for us to maintain, tune and automate.

There’s also few other bits (nibbles?) of data news:

• We won’t be producing a data dump for the month of December 2010, but you can definitely expect one just after the new year. We apologize for the delay.
• SEDE will continue to be updated monthly as a matter of policy to keep it in sync with the monthly data dumps.

Remember, SEDE is fully open source, so if you want to help us hack on it, please do!

code.google.com/p/stack-exchange-data-explorer

And as usual, if you have any bugs or feedback for us, leave it in in the [data-explorer] tag on meta, too.

Our core functionality, as always, is Q&A — asking great questions and providing great answers. You could certainly go months or years without ever needing to visit anything beyond the main site. But that’d be a shame.

Chat – Our Third Place

Did you know that real time web chat is a standard “out of the box” feature on every Q&A site we launch? Not just any old generic web chat, either — we built our third place from scratch to be a best-of-breed next generation chat system. We now have what is, in my not so humble opinion, the best web chat software I’ve ever seen or used. Really! You should check it out.

To visit chat, simply click on the chat link in the header:

Or, on some sites, we have a live preview of two chat rooms in the sidebar; click through to visit and start chatting.

But it doesn’t matter what I think. Everyone should check chat out for themselves and decide if it’s worthy or not. That’s why we introduced the Talkative badge.

Posted 10 messages, with 1 or more starred, in chat

To earn this badge, you’ll need to post 10 chat messages in a room — and one of them must be starred by another fellow chat user user. Go be interesting!

Area 51 – Our New Site Creation Zone

Did you know that the reputation you earn on a Stack Exchange site is good for more than additional privileges on the site? That’s right. The more reputation you have in our network, the more weight you also carry on Area 51 — our new Q&A site creation zone. The democratic, open community process defined at Area 51 is the only way to create new sites on our engine — just like it says in the FAQ.

The success of this community process depends, as they all do, on participation. We’ve also found that our Q&A sites work best when they are led by experienced users with reputation in one or more existing Stack Exchange sites. That’s why commitments by experienced users are weighted so heavily on Area 51, and why we introduced the Precognitive badge.

Followed the Area 51 proposal for this site before it entered the commitment phase

This badge, like Area 51 itself, is all about the future. To achieve this badge, you’ll have to follow an early Area 51 site proposal that eventually succeeds and go to beta — hopefully with your active assistance. In other words, the only way to earn the Precognitive badge on a site is … before the site even exists! Spooky, right?

Enjoy these new badges — as always, we welcome feedback on chat and feedback on Area 51, but you’ll need to find them first!