More fsync and write Reduction

As you may or may not be aware, my personal mission as of late is to reduce the number of writes and fsyncs that Firefox makes, and move the ones that we do have to make off of the main thread. The primary target here has been Places, and the work is still continuing.

The Firefox team has been focusing on code sprints to get some small well scoped things done for Firefox 3.1 since we’ve got a bit more time. My latest sprint can be found over in bug 480211, where I’ve removed a write and fsync that we used to do after every page visited. If we had enough pages in history that were old enough, we would remove them from history. We now do this off of the main thread, asynchronously at the same time we flush data from our temporary tables to our permanent ones. The net result is the same number of writes and one less fsync. Additionally, the write is no longer done on the main thread.

Sadly, I couldn’t measure any real-world performance gains with my DTrace scripts – in fact I saw no change during several different runs of Tp3 with various places.sqlite files. It’s quite possible I did not have the conditions setup correctly to have pages expiring, and I could have spent a few more hours generating just the right places.sqlite file to demonstrate wins in the real world, but the theory behind the patch is pretty simple. The gain is pretty obvious.

Just another drop in the bucket of performance wins for Firefox. Stay tuned, as there is more to come!

By Shawn Wilsher

The man behind the site.