[yk]

With most software, well most software is pretty inefficent and profits from HT. However there are a lot of reasons for that, writing in something interpreted because it is faster to develop and the software does not need to be very efficient in the first place would be one application. (Not to say that all Python/JS/etc is inefficient, just that software that needs to be efficient is precisely the kind were one would consider an unmanaged language.) Additionally, things like webservers or dbs often just don't know which piece of data they need next, simply because they don't know the next query, have a tendency to profit from HT, even though the software is hardly known for being inefficient.

[paulirwin]

FWIW, you mention databases, but even some database workloads can have better performance with HT turned off. I first learned this from a DBA at a former job when I was curious as to why they turned HT off. A member of the SQL Server team back in 2005 ran some experiments and found that you can get a 10% performance improvement in some workloads with HT off [1]. I don't know how much of that is still true today, however, as nearly all of my recent experience is PaaS in the cloud.

[1]: https://blogs.msdn.microsoft.com/slavao/2005/11/12/be-aware-...