PHP

MySQL backup is sometimes very hard to do effectively. MySQL provides various options for backup, but many of them are simply unsuitable for large systems, particularly if they need to remain active during backups. Percona's XtraBackup is an open-source clone of InnoBase's InnoDB Hot Backup utility. So what makes XtraBackup a better solution, and how does it work?

Update: on December 10th 2009, Percona released Xtrabackup 1.0.

Continue reading "MySQL backups with Percona's XtraBackup"

Google's charting API has been around for quite a while now, but I've only just needed to actually look at it. It became immediately obvious that I needed a PHP encoding function, so off to google I went. Though I found several implementations, they were all incomplete or deficient in one way or another (and it didn't help that there was an error in google's extended encoding docs), so I've written my own based on several different ones. Both simple and extended encoders support automatic scaling, inflated maximum and lower-bound truncation, so you can pretty much stuff whatever data you like in, with no particular regard for pre-scaling and you'll get a usable result out. They have an identical interface, so you can use either encoding interchangeably according to the output resolution you need (contrary to popular belief, the encoding to use has very little to do with the range of values you need to graph). By default, the full range of possible values is used as it just seems silly not to. I deliberately omit the 's:' and 'e:' prefixes so that you can call these functions for multiple data series, and I include a function that does just that. You still need to generate your own URLs and other formatting, but that's a different problem. Read on for the code... Continue reading "Google Charts API Simple and Extended Encoders in PHP"

I've just had a slightly tricky time upgrading a subversion repository on sourceforge. They have recently added support for subversion 1.5 at the server end. 1.5 brings major new features for merging, but as it's not backward compatible with older subversion clients, the upgrade is not done automatically. SF have also done a major rearrangement of their documentation while transferring everything to Trac, and it's not always easy to get the right info. Normally to upgrade a subversion repo, you just run the 'svnadmin upgrade /path/to/repo', however, it's not quite so simple on sourceforge as you don't have direct access to the repo, and the instructions they give are slightly wrong at the time of writing. You're likely to get an error like this (it's not obvious that this is a fatal error) when you reload a dump file:

svnadmin: File already exists: filesystem '/svnroot/projectname/db', transaction '443-0', path 'tags' \* adding path : tags ...

This is because load is intended to add files to an existing repo, not to replace those that are already there, so you need to wipe the repo and start from scratch. So, here is a working command sequence that needs to be run from a project login shell on sourceforge (it applies to the project you're logged in through, substitute your project's name for projectname):

adminrepo --checkout svn svnadmin dump /svnroot/projectname > svn.dump rm -rf /svnroot/projectname/\* svnadmin create /svnroot/projectname svnadmin load /svnroot/projectname < svn.dump adminrepo --save svn

Yes, you do need to delete the whole thing and re-import it, but it's quick and easy, and you have a backup in the dump file you take at the start. After the upgrade, make sure you get a new checkout of your project to ensure that you're using 1.5 all the way through. Now you'll find that commands like 'svn merge --reintegrate' work.

When you're developing web stuff, working with projects in path names (i.e. not at the top level of a domain) can be difficult (gets in the way of absolute links, rewrite rules etc), so you often need to set up a local apache virtual host, stick an entry in DNS and create an SSL certificate before you can get on with the serious business of doing some real work. This can get to be a drag when you do it a lot, but there is an extremely elegant solution that means you'll never have to do it again... Continue reading "The web developer's holy vhost trinity"

Someone at AMEE pointed out to me that there's been a flurry of activity around so-called "Web Hooks" when I referred to the concept. This is quite heartening as I thought of this a couple of years ago and implemented this in Smartmessages early last year! I call them callbacks, but the idea is the same - it's essentially a distributed observer pattern. I couldn't figure out why nobody seemed to understand what I was on about... When I get some interesting event (e.g. a message open, mailshot completion, clickthrough etc), I ping a user-supplied URL with the appropriate event data, pretty much the one-liner that Jeff alludes to. The reason we do it is that sync with external systems (usually CRM) is something that were always running into, and there seems to be no sensible, generic way of dealing with it other than this, so I'm surprised it has not been discussed in this context before. There's one downside as far as I can see - it is highly dependent on the receiver to be able to handle the event in a timely fashion. This isn't an issue if you're connecting say, Yahoo! to Google, but it could be a big problem if you connect Google to your Wordpress blog... My experience of CRM systems is that they are simply too slow to cope with the high rates of traffic that we are likely to generate, for example, if we point a stream of ~200 events per second at a CRM system, it will probably just bog down and fail (I'm thinking of the SalesForce API here which typically takes 1-2 sec to deal with a single SOAP API call). Retrying will only make this worse. I have two solutions for this: limit events to those that don't happen so often (kind of lame!), or alternatively, use an outbound message queue to rate-limit the sending (Amazon SQS and Memcacheq spring to mind). Queueing works, but you lose some of the real-time aspect. Ideally clients would implement their own incoming queue in order to allow them to process events at their leisure, but this is mostly beyond the vast majority of web authors (or at least those that host the CRM systems that we hear from!). Anyway, it's nice to know that I'm not completely barking...

From this truly excellent conference, I took away some good memories, some new ideas and a nasty bout of conference flu. There's nothing quite like being in close proximity to a few hundred people to really spread things around... Highlight for me was Aral Balkan's keynote. It's always nice to see someone showing plain enthusiasm, and I couldn't agree more with him about the "lost magic" of computing. Had a chat with him afterwards about AMEE and other things. He also seems to have put together some odd but dull things that I had noticed a need for - EU VAT codings and ISO language references as web services! I didn't really enjoy David Soria Parra's talk on sharding. It all came across as very negative and many of the ways of doing it and coping with the fallout were not really discussed. No mention of MySQL 5.1's partitioning (which is limited, but is at least a start), or more radical approaches like Sequoia. David Axmark's talk on Drizzle was more interesting than I expected, nice to see effort being put into this direction. Microsoft really does seem to be trying a bit harder these days - their CSS test suite for IE8 is very welcome, and the effort they are putting into PHP, apache and other projects benefits many people. It has to be said that while it's not a mainstream product, Surface is really pretty cool to play with. Chris Shiflett's talk was excellent too; his demos and examples were particularly good, and entertaining. The post-conference social was great fun, I met lots of nice new people. After our move to France I suspect it will be harder to get to events like this, so I should make the most of them while I can! I've had several ideas for talks that I'd like to do (I get sick of email sometimes!), so I guess I need to get a bit more proactive on actually submitting them to a call for papers.

This article on highscalability.com is a really excellent rundown of some of the options available for scaling a site to the heights of Digg. Ironically enough, at the time of writing the highscalabilitycom web server shows this error:

Unable to connect to database server The MySQL error was: User highscal_admin already has more than 'max_user_connections' active connections.

I can point them at this really good article on how to avoid problems like this... oh, wait...

I finally got my 'Genius' rank in PHP on Experts Exchange today. It's taken about 3 years and in that time I've answered over 1,000 questions and participated in over 500 others, making about 3,300 posts. I think I've helped a lot of people, but I've learned a lot too. And I get a free T-shirt. Now why did I choose such a silly user name?