Friday, 11 December 2009

A question of prudence

Some time ago (and by “some time”, I mean “roughly eleven years”), I came up with an idea for a strategy game that would be grander in scope than all other strategy games. I don’t recall if it was to be multiplayer (though I doubt it), but I recently realised that, using social platforms like Facebook, MySpace, OpenSocial, &c., it’s quite doable, and with a gentle nod to the strategy games of yesteryear.

Now, I’ve forgotten, in the intervening decade, a lot of the detail. I seem to recall that the original version was supposed to include a first-person mode, which I’m uncertain if I’d be able to create even now. I knew I couldn’t then, and I doubt, highly, that with a social platform, first- or third-person view would even be an option. I’m not exactly what you might call “proficient” with applications like Flash or Silverlight.

I’ve started to write some of the plans down about how the game mechanics might work. I’ve found that, with the proper planning, it could allow players to control not only vast empires, but even small parcels of land, or even just groups of AIs. Players could govern each other under the right circumstances, and a player whose empire was governed by another could feasibly rise up against his former master.

It almost wouldn’t be a game, as much as it would be a simulation, on a grand scale, of the development of intelligent civilization (and yes, I know, there’s already a popular franchise of strategy games with that name… this game would be, in general, a step removed from the necessary micromanagement that I find Mr Meier’s game espouses). The difficulty that I have is that I want to talk about it, but I don’t want to have my ideas stolen by a programmer with more time, or (more likely) a team of subordinates to do the work. Any suggestions for how I could discuss this notion? I'm afraid that if I let my momentum flag, it’ll be another ten years before anything gets done on this!

Thursday, 5 November 2009

In which the author learns that any great Web application developer needs to be half DBA

The latest section of study in my database tuning class has focused on transactions and crash recovery. As with table indices, I’ve been aware of transactions on, shall we say, a theoretical level: I knew what they were, and I knew that they were useful for grouping queries together for atomicity. However, it somehow didn’t occur to me how spectacularly important they are if you’re writing a web application that has relation constraints, in order to maintain database consistency.

Perhaps it was merely that my previous argument had been, “but each request will be executed in less than a second!” That doesn’t matter when you’re trying to serve content to, say, more than ten thousand requests in an hour. On average, that’s one request every 0.36 seconds. But we all know that it doesn’t work out like...

  1. 0:00.00: Request
  2. 0:00.36: Request
  3. 0:00.72: Request
  4. 0:01.04: Request
  5. 0:01.40: Request
  6. &c

That just doesn’t happen. At ten thousand requests per hour, you will almost certainly see overlap in your requests. This means, of course, that if you have an application that involves relational constraints, foreign keys, and really, anything where you have to reflect a change in table A in table B in such a way that every request is consistent, that change has to be applied to both tables before another request is allowed to query either. This is why you need transactions.

I never really thought about it in terms of even modest usage patterns like that. The textbook went over it in more depth, more in a context of what considerations a DBMS programmer has to be aware of, but it was a great reminder. Just two concurrent transactions, one writing two tables, and another reading those two, can display errors in the data if the read transaction reads table A after it’s been changed, but reads table B before its change has been applied.

It retrospect, it’s so obvious. Unfortunately, I haven’t ever—and I mean ever, in my entire professional career—met a web application programmer who actually used transactions, and didn’t just blithely let their database autocommit every update as soon as the query was completed. Nobody does this, and why? At a guess, because it takes extra programmer time. Only one PHP framework I know of forces transactions by default (hint: It’s not Zend… something else I need to add in to my Still Unnamed Project), but what about developers making their own frameworks? Not using frameworks? Using a framework that relies on the programmer to specifically start transactions? It won’t happen, because so much emphasis is put on reducing programmer time that no one really, properly, considers taking the extra hour, or day, or even, at worst, week, to plan things ahead and properly insulate against failure from step one.

But it does go to show how important proper planning is to being able to do this kind of work properly. Proper analysis of your tools and knowledge on the programmer’s part of what needs to go in to the software is what makes for better software in the long run. Seriously, take the little bit of extra time to do it right, and improve your product’s performance. How much does a day or two cost—once—relative to how much an extra server costs every month to compensate for inefficient code?

Thursday, 19 March 2009

You learn something new every day

I’m willing to admit when I’ve been wrong, mistaken, or just poorly informed about something. I’m always happy to learn new tricks, and useful ways to improve my productivity, and my code’s efficiency… but a lesson I just learned last night takes the cake for things I wish I’d known years ago.

After more than two years spent outside of studying, I’ve finally started to get things back in gear to complete my B.C.Sc. degree (Brief explanatory digression: I had to suspend my studies a year before they were finished due to lack of funds, and then a series of layoffs after moving to Toronto has consistently interrupted my ability to resume). I’m currently taking two courses by correspondence: Small Business Management and Distributed Database Systems and Database Tuning. The first topic in the DB Tuning course is a brief analysis of difference database indexing methods, in terms of how the DBMS manages the pages and records under certain structures. I’ve been seeing indexing options for years now, fiddling with phpMySQLAdmin, but I’ve never really been clear on how the indexing worked, from an internal point of view. Never looked into it, just as I never looked into JOINing tables instead of relying on the WHERE clause… and when the light went on, reading the textbook, it nearly blinded me.

I’m not going to get into the details of it here, primarily because I don’t feel 100% confident in my correct understanding of the mechanisms used, but I realise now that I’ve been treating my databases as magical blackboxes a little bit too much. It’s a pretty rich statement, coming from the guy who says he does his work better when he has a more thorough understand of the whole system, from top to bottom. This kind of thing certainly demonstrates how true that is, though. For, literally, years, I’ve been treating DBMSes as though they just magically know how to organise my data to be able to get at the records I need quickly. I’ve strongly espoused letting the database do the hard work of returning a specific set of tuples, instead of pulling back a huge range of candidate tuples, and letting the host language (PHP, in my case) decided yea or nay about each record, on the grounds that the DBMS has been designed to do that kind of thing, and really well. And I’d like to think that’s still true, but man alive, it’s clearer than ever that I still have a lot to learn about writing database driven applications.

On that note, I unfortunately have to admit that my Zend enhancement/application template has stalled. But don’t worry, I already have an excuse lined up and ready to go: between my new job, going back to school and a play that’s been in rehearsal since the beginning of the year, I’ve had precious little time to work on my own, personal projects, which is unfortunately what that project is. Educational, certainly. Valuable to the wider community? Possibly. An interesting problem to work, most certainly. But also something that is simply not my highest priority, and my time feels pretty stretched most days. Besides, I’m still stuck at the logging functionality and integrating it better as a Model, and in turn, redesigning my Model superclass. I've been debating whether or not I should create an Object superclass as well, for better adherence to MVC, or whether that would just be unnecessarily reinventing the wheel (unlike the project, which I feel is a fairly necessary reinvention of the wheel).

Wednesday, 14 January 2009

Sometimes, reinventing the wheel becomes necessary.

I believe I’ve found that a previous entry, A Model! A Model! My kingdom for a Model!, was written, perhaps, a little hastily. Some further analysis, and review of another Zend-based project, has revealed that the Zend_Db functions do provide some Model functionality, with the Zend_Db_Table and Zend_Db_Tablerow classes.

However, I maintain that they’re ineffective as a Model, if for no other reason than it restricts to user to thinking of Models as extensions of the database. This is simply not true. The Model should just exist as an abstract, and if the application requires for the majority of the Models to be stored in a database, then by all means, it should put them there. But the framework shouldn't necessarily require it.

I’ve come to that opinion while working on my own ZF application template. I realised over the Christmas holidays that my own Model class is somewhat restrictive… because it requires the database! I've since forgotten how I came up with the idea—I think it had something to do with storing uploaded images in the filesystem, rather than as binary blobs in a database, that I realised that a Model should really be more like an interface, with find(), set(), write(), &c. methods that need to be implemented by, say, a triad of DatabaseModel, FileModel and MemoryModel classes. Perhaps even a SessionModel or CookieModel, but I think that might be pushing it.

I’ve been giving this same notion a little bit of thought over my recent hacking runs as a solution to a problem I’ve been running into. What's happening is that I want to implement a combination flash messenger and logger. Why? Well, it’s (I hope) fairly simple.

During a given execution of the application, any number of messages may need to be delivered to the user. Say, for example, a user wants to upload five images to the application. Four of them work, and we want to tell the user this, but one of them failed, and we want to tell the user this, as well. ZF’s FlashMessenger can kind of do that, but either all the messages have to appear in the same context, or the messages have to be rendered on the way into the messenger. This isn’t ideal, for the simple reason that it’s putting View logic into a Model. Thanks, but no.

So, I thought that, since I’m already using Zend_Log to capture runtime information that I might want displayed in a debugging situation, maybe I could pull the logged information out of that in the layout. No such luck; Zend_Log doesn’t let me access its writers. After that, maybe I can write my own Zend_Log to write to a Zend_View’s placeholder, right?

If only it were actually that simple. I don’t really want to think about how much extra effort that’s going to involve, wading through the verbose, but less-than-useful ZF Reference Guide, the less-verbose, sometimes-useful ZF APIs, and just digging through the actual code to figure out how all this stuff fits together.

Or, I could just go the route I’ve already been going with my Model and Database classes, and roll my own functionality that does what I need it to do. Part of the point of this project was to identify the parts of ZF that fall short of what I, and possibly other programmers, need, and fill in what’s missing. To have a skeleton of an application pre-built that offers a lot of highly-useful, rarely-requested features.

I’m starting to think that as time goes on, I might wind up having to replace some more core elements of any MVC framework so that things in my own stuff work together more smoothly. God knows, I might even wind up building my own framework out of this!

How that affects my desire to move away from PHP and towards Python is, as yet, unknown, but it might help. It’ll certainly provide a hell of a groundwork for a first project in a new language!