Very large entry sizes or a large number of entries can negatively impact server performance during import operations. Both Directory Server settings and operationg system settings can be tuned to improve performance for imports.
10.1. Importing Entries with Large Attributes
nsslapd-cachememsize attribute defines the size allowed for the entry cache.
The import buffer is automatically set to 80% of the cache memory size setting. If the memory cache is 1GB, for example, then the import buffer is 800MB.
When importing a very large database or entries with large attributes (often with values like binary data like certificate chains, CRLs, or images), then set the
nsslapd-cachememsize attribute high enough so that the import buffer has enough memory to process the entries.