Hi Team,

We are experiencing high memory usage on  our Mongodb secondary servers in a 5-node replica set. The memory usage does not align with the configured cache and free heap values, leading to unexpected memory growth. Despite a recent upgrade from MongoDB v7.0.9 to v7.0.14, this issue persists.

MongoDB Version:
7.0.14

Operating System:
Ubuntu 22.04.3 LTS (Jammy Jellyfish)

Issue Details:

1. Current Configuration: MongoDB cache is set to default values.
2. Memory Usage Pattern: Over two days, memory usage on the secondary server increases by around 12 GB, which does not correspond with cache + free heap usage expectations.
3. Observation Post-Upgrade: The issue persisted after upgrading from MongoDB v7.0.9 to 7.0.14.

root@dbserver04-cds:/home/mydbops# free -h 
               total        used        free      shared  buff/cache   available
Mem:           123Gi        65Gi       796Mi       1.0Mi        56Gi        56Gi
Swap:           49Gi       585Mi        49Gi
root@dbserver04-cds:/home/mydbops#

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND                                                                                                                                 
2916728 mongodb   20   0   64.9g  63.3g  36096 S  68.0  61.4 678:07.12 mongod      

Actions Taken So Far:
Upgraded MongoDB to the latest stable version within the 7.x series.

Expected Outcome:
Memory usage should correspond with cache and heap configurations without unaccounted increases over time.

Assistance Required:

Help identify potential causes of excessive memory usage beyond cache + heap limits.
Provide recommendations for further configuration adjustments or diagnostic steps to track down the source of high memory usage.