Q. If upsert is a delayed operation, how long can it potentially take for the results to appear, and what does it depend on? (2016)
A. The results will appear in Tarantool immediately. The operation is called delayed in terms of LSM tree-based algorithms. Upsert puts a ‘tombstone’ in the top tree (C0), similarly to deletion.
When you’re searching for the results later, Tarantool will check all the trees and find what needs to be done - upsert a new tuple or apply upsert to an existing one.