In the example below, database writes are concurrent at the points in time t1 and t2 and happen before a sync can communicate the changes. However, writes at times t4 and t6 are not concurrent as a sync happened in between.

Time CRDB Instance1 CRDB Instance2
t1 SET key1 "a"
t2 SET key1 "b"
t3 — Sync — — Sync —
t4 SET key1 "c"
t5 — Sync — — Sync —
t6 SET key1 "d"