RAM increases and decreases irregularly and tends to increase gradually

[Thanh_Nguyen_Van]

I use mongodb version 4.0.28.
Search engine: WiredTiger
Oplog Size: 750Gb
Server configuration: 64CPUs, 496Gb RAM.

I’m experiencing a situation where RAM keeps increasing and then suddenly decreasing. Over time, the RAM peak increases.
Why does this phenomenon occur? I can handle it.

[Peter_Hubbard]

Hi Thanh, this looks like the cache filling up. When it reaches a certain level, some background threads will automatically start evicting older data in the cache. Can you correlate the memory usage with your query usage?