Recent Xcode 7.3 Performance regressions

We recently discovered some changes that have resulted in many of you experiencing a regression in the performance of your builds that use our xcode7.3 OS X build environment image. I wanted to share with you why this performance decrease occurred.

After reports from multiple users about an increase in their build times under Xcode 7.3, we investigated and we discovered that the Xcode 7.3 GA release image we published on March 24th was accidentally published with four virtual cores, which is not the correct value we intended to have, based on our current OS X infrastructure.

Since we rolled out a new and improved OS X infrastructure last year, we’ve provided OS X virtual machines with one virtual core and 4GB of RAM. However, when we published an update to our Xcode 7.3 image with xctool 0.2.9 on Apr 19 at 19:15 PST, this new image was correctly setup with one virtual core. This resulted in a performance regression for any users of the 7.3 image.

I am sorry for the confusion this has resulted in. We are aware that providing more cores is very beneficial to performance, especially with the recent Xcode 7.x releases. However, the infrastructure costs of our OS X virtual machines is significantly more than similar sized Linux virtual machines, so adding more capacity to support increasing the base size of the OS X virtual machines is something we’re still in the research and testing phase on. We hope to have more news on the future of this in Q3 of 2016.

If you have any further questions about this, please email