What is the content of the segment file in node/0/_state


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?

Hi @verdantyang and welcome!

The index under nodes/0/_state holds the same internal information as in the *.st files in earlier versions, just more efficiently since it uses Lucene. This was introduced in 7.6.0.

Thanks @DavidTurner