Hi,

A memory-mapped cache is a segment of virtual memory that has been assigned a correlation with some portion of a resource.

LDB cache is on disk, meaning: an I/OS is required to retrieve the data.

Basically:

The nss_sss memory-mapped cache is consulted first (extremely fast).

If not found in nss_sss cache the request is passed to the sssd_nss module.

Then sssd_nss checks the SSSD on-disk LDB cache. If the data is present in the cache and valid, the nss responder returns it.

If the data is not present in the LDB cache or it is expired, it connects to the remote server and runs the search.

I think this nice article will give you the concise answer:

http://www.ateam-oracle.com/part-1-of-4-sssd-linux-authentication-introduction-and-architecture/

Regards,

Dusan Baljevic (amateur radio VK2COT)