By "DB rock" do you mean "DB lock"?
There is no "secondary db", I will consider "secondary node". Yes, the node can read and also even write to the local database while synchronization is taking place. Both on the primary and on the secondary nodes.
Your application will use Node.js on both the primary and secondary nodes?
better-sqlite3 as the wrapper for Node.js. The downside is that it is synchronous, but it solves a lot of problems.
Maybe the "db lock" problem is related to
node-sqlite3? Is it OK to use
better-sqlite3 in your application instead?
With the commercial license your company gets access to our git repository as well as to pre-compiled binaries if you do not want to compile it by yourself.