How does Redis 6.0 use radix tree to do key expiration

[Peter]

Hi, 

The 6.0 RC3 release note indicates that "Now the timeouts have HZ

resolution regardless of the number of connected clinets. New timeouts
are stored in a radix tree and sorted by expire time." 

But I do not understand how Redis store the timeouts info in a radix tree. I found antirez's old posts in twitter. 

Is that how they implemented the radix tree in 6.0? 

Thanks