WT makes use of the system API call sched_yield() through the portability wrapper __wt_yield(). However on Linux this call is non-deterministic unless used with the real-time scheduling policies SCHED_FIFO or SCHED_RR.

WT threads uses the default scheduling policy SCHED_DEFAULT also know as SCHED_OTHER.

The default Linux manual page is scornful of the use of sched_yield with the SCHED_OTHER policy:

sched_yield()  is intended for use with real-time scheduling policies (i.e., SCHED_FIFO or SCHED_RR).  Use of sched_yield() with nondeterministic scheduling policies such as SCHED_OTHER is unspecified and very likely means your application design is broken.

In consideration of this, revisiting the expectations and use of __wt_yield() is merited.

Notes:

• Windows porting layer uses SwitchThread() which has clear semantics.
• The behavior of sched_yield() in the MacOS microkernel should not be assumed to be the same.

This ticket is ambiguous as it involves research and consensus building as a prerequisite to any actual coding required.