Out of sync but this session needed a posting of it’s own - a quick 35 minute session by Steve Souders (Chief Performance Yahoo!) from Yahoo about YSlow. Funnily enough I was catching up with the ColdFusion Weekly PodCast 2.26 on my commute into town on the very subject.
We’ve all seen YSlow I’m sure so don’t need to go into much detail but the short story is that our webserver performance may only account for around 5% of the total time of their ‘visit’ with other external factors coming into account - their tool YSlow highlights such things. He ran through the 14 rules/guidelines published by Yahoo - one of note was to move script files to the bottom of the page as they’d block other stuff running - don’t they need to be in the head? He also spoke about a big in Firebug on the NET tab that shows asset load responses. In a new version of YSlow (out Friday apparently) it will have a option in the options menu to patch Firebug so that the NET panel does not include locally cached objects. If you inspect a page with Firebug it will show all the objects irrespective of if they’ve come out of cache - whilst Live Headers will show the request was never made. This apparently has caused some confusion and something that Yahoo will be addressing in their next YSlow release.
And yes, even in this session someone asked what a CDN is. I’m attending a 4 hour workshop by Steve on Friday so will have much more detailed notes after that session.
October 3rd, 2007 at 8:04 pm
One thing to be aware of is that the ySlow extension forces a second execution of the page being viewed in order to do its analysis. Normally this is not an issue, but occasionally with cf, you might be stopping execution of an update template while debugging to track down some issue. If you do this, you will see any queries that were run in the template execute a second time. If you don’t realize that ySlow is running, you can be chasing some strange red herrings for a while until you figure out what is causing the strange behavior.