Harry wrote a really good article all about the performance measurement Time To First Byte. Time To First Byte: What It Is and Why It Matters:
While a good TTFB doesn’t necessarily mean you will have a fast website, a bad TTFB almost certainly guarantees a slow one.
Time To First Byte has been the chink in my armour over at thesession.org, especially on the home page. Every time I ran Lighthouse, or some other performance testing tool, I’d get a high score …with some points deducted for taking too long to get that first byte from the server.
Harry’s proposed solution is to set up some Server Timing headers:
With a little bit of extra work spent implementing the Server Timing API, we can begin to measure and surface intricate timings to the front-end, allowing web developers to identify and debug potential bottlenecks previously obscured from view.
I rememberd that Drew wrote an excellent article on Smashing Magazine last year called Measuring Performance With Server Timing:
The job of Server Timing is not to help you actually time activity on your server. You’ll need to do the timing yourself using whatever toolset your backend platform makes available to you. Rather, the purpose of Server Timing is to specify how those measurements can be communicated to the browser.
He even provides some PHP code, which I was able to take wholesale and drop into the codebase for thesession.org. Then I was able to put start/stop points in my code for measuring how long some operations were taking. Then I could output the results of these measurements into Server Timing headers that I could inspect in the “Network” tab of a browser’s dev tools (Chrome is particularly good for displaying Server Timing, so I used that while I was conducting this experiment).
I started with overall database requests. Sure enough, that was where most of the time in time-to-first-byte was being spent.
Then I got more granular. I put start/stop points around specific database calls. By doing this, I was able to zero in on which operations were particularly costly. Once I had done that, I had to figure out how to make the database calls go faster.
Spoiler: I did it by adding an extra index on one particular table. It’s almost always indexes, in my experience, that make the biggest difference to database performance.
I don’t know why it took me so long to get around to messing with Server Timing headers. It has paid off in spades. I wish I had done it sooner.