I searched on this forum, and i do see this question came up before, but I still think this worth mentioning.
I am not here to question why it would current implementation takes that much memory.
My Sync Folder contains about 56632 files, and folders are: 575GB in size. Running on Ubuntu 16.04 and rslsync uses about 9.1 GB RAM. (CPU fluctuates between 5-8% during running)
For a comparison, i also use Dropbox Pro, I have 26602 files and 79GB in size. Dropbox uses about 329MB RA
And still I'll explain it, which may help to find a solution. This has been already explained multiple times on forum, but here it goes.
RAM is taken by database files. Database keeps record of each entry in the sync share - currently present files and the ones that have ever been in the share. Entry - is the file itself, and also each subdir level in its path. Each entry takes up around 2KB of RAM. The bigger folder tree you have, the more nested folders, the more file changes/deletions, the