Indeed Engineering Blog is the company blog of the job site's engineers, covering Java, Linux, CI, and infrastructure performance.
HN commenters cite its detailed posts on CPU throttling fixes in the Linux kernel and on its LSM-tree architecture.
I'm not aware of any effort to retire tiered compilation. It was even promoted to be the default in Java 8 (2014). http://www.oracle.com/technetwork/articles/java/architect-evans-pt1-2266278.html
The only downside I'm aware of is that it increases the pressure on the code cache. If your code cache is not large enough, it will thrash as methods are discarded then recompiled. We had significant performance problems with a server and it took quite awhile until we realized that was the cause. A cache of 256 mb was more than enough for us running a 2 million LOC monolith under Tomcat, so the absolute memory use isn't that significant. (Reference we found while researching: http://engineering.indeedblog.com/blog/2016/09/job-search-web-app-java-8-migration/).
Once you know this is an issue, it's easy to monitor, but it is one more thing that can go wrong in the JVM.
"Contract won't or shouldn't change" seems unrealistically idealistic to me. Java migration - or any platform for that matter - is not just migrating its language features but also its ecosystem - runtime, VM, GC, frameworks.
There are many examples of migration problems for any platform - just have to google it. When information that can challenge our assumptions is just a google search away, I don't see why one should hold on to blind faith in idealistic assumptions. Here's one writeup of a system whose performance suffered simply by migrating to Java 8 without involving any code changes [1].
[1]: http://engineering.indeedblog.com/blog/2016/09/job-search-web-app-java-8-migration/
> https://engineering.indeedblog.com/blog/2019/12/unthrottled-fixing-cpu-limits-in-the-cloud/
This is a more detailed post on the same thing - part two indicates changes have been back-ported to a number of kernel versions:
Linux-stable: 4.14.154+, 4.19.84+, 5.3.9+
Ubuntu: 4.15.0-67+, 5.3.0-24+
Redhat Enterprise Linux:
RHEL 7: 3.10.0-1062.8.1.el7+
RHEL 8: 4.18.0-147.2.1.el8_1+
CoreOS: v4.19.84+
Indeed published a pair of blog posts back in 2013 on how they evolved their architecture to use LSM trees.
Part 1: https://engineering.indeedblog.com/talks/1-1-billion-evolution-document-serving-system/
Part 2: https://engineering.indeedblog.com/blog/2013/10/serving-over-1-billion-documents-per-day-with-docstore-v2/