Continuing the outlook for wait events which are out of place comes a post about the mystery behind the "GV$: slave acquisition retry wait time" wait event I have encountered on 12c. My MOS research found two articles which are on point, but neither of which makes a whole lot of sense:
WAITEVENT: "GV$: slave acquisition retry wait" - Note ID 371117.1
This document talks about a list of instances, and thinking there is a configuration change in process until it no longer thinks the configuration change is going on. This was something I could not understand because nothing seemed to be reconfiguring, and the document did not point me to a specific thing I could look at to see if it was reconfiguring. After a few weeks of this being very low on our wait event alert, it eventually went away.
Wait Event GV$ Slave Acquisition High With CURSOR_SHARING To FORCE - Note ID 1589592.1
This article was referring to the parameter (in gv$parameter) cursor_sharing being set to FORCE, which we did not have it set to, and leading to a buffer value needing to be changed. There was no changing the value before it went away, and we even had the value higher than the recommendation!
Since it went away, and we could not narrow down what was going on, I am sure I will see it again in the future and when I nail this one down there will be an update here. :}