Elasticsearch gradually occupy the memory and free it suddenly

Elastic Stack Elasticsearch
1

Hi, there I have missed a new issue: elasticsearch occupy and free the memory regularly.
Just like the image:

que.png1330×344 207 KB

Can anyone tell me the reason? Thanks very much.

2

That kind of thing is normal. Unless you are seeing problems then I
wouldn't think about that. JVM heap usage usually saw tooths, raising
slowly and dropping quickly. I don't know what you are graphing there but
it looks to raise quickly and drop slowly. Available heap? Some other kind
of memory?

3

Thanks for you reply me. On this machine,I installed only ELK softwares . The graph there shows the available memory on this machine. The green area means the available memory.So, it looks to raise slowly and drop quickly. About 22 hours is a cycle.