Index should fit in RAM or in cache?

[Alaskent19 (Alaskent)]

Hi to all,

the documentation is not very clear if index should fit in WiredTiger cache or in RAM?

Thx

[Prasad_Saya]

Hello @Alaskent19,

Here are some related links from documentation:

• Ensure Indexes Fit in RAM
• How can I see the size of an index?

[Alaskent19 (Alaskent)]

Hello @Prasad_Saya,

but I don’t understand if the documentation refers to the total RAM or only to the WiredTiger RAM.
I have a machine with 8GB of RAM … how much RAM should I consider for index and working set?

Thanks

[Prasad_Saya]

I think the RAM / memory refers to the total physical RAM available on the server (or specific node).

Also, see these articles:

• From the MongoDB blog Performance Best Practices: MongoDB Data Modeling and Memory Sizing see the section Memory Sizing: Ensure your working set fits in RAM

• Atlas Sizing and Tier Selection - Memory

• Discussion on this forum: Working set MUST fit in memory?