What is the chatLengthEstimator.cmsketch file located in the Library/Suggestions folder? (Mac OSX) I stumbled upon the Suggestions folder /Users/zezuz/Library/Suggestions  while browsing through my MacBook Pro, running High Sierra. (which btw, I never knew even existed) 

In the folder is a file named chatLengthEstimator.cmsketch. I tried to view it but no program I have can open a .cmsketch file. Clicking the "search App Store" option resulted in nothing. 

A google search also returned little, but it seems that it's some sort of sample or database file, possibly related to TIDB?

My questions are: 


What is a .cmsketch file? 
What is, specifically, the chatLengthEstimator.cmsketch file and why is it being "suggested" to me? 


Thank you in advance for your help!
The files in ~/Library/Suggestions are used internally to support some of macOS's machine learning features, like Spotlight Suggestions, Suggested Contacts, and data detectors. These files are not being suggested to you.

A .cmSketch file probably contains a count-min sketch data structure. It does not contain any human-readable data. Given the name of this file, it is probably used to estimate how often, or for how long, you chat with your contacts on iMessage.