ES 6.* only stores .st files in the /nodes/0/_state directory to record node status information.
But under the ES 7.12 version, I found segment-related file in /nodes/0/_state directory, such as segment_N and .si.
In my opinion, the segment-related files only exist in the indexes directory of the index.
I am curious about what is stored in the segment file in the /nodes/0/_state directory,
and which version started to introduce this design . Can someone help me with this doubt?