Partitioning

Rebalance Hash

Hash rebalance changes the modulus and recomputes moved keys.

highlighted = computed this step

Hash rebalance changes the modulus

Hash rebalance in this exact model adds one partition. That changes the modulus, so many keys may route to different names. Note: this is not consistent hashing.

hash modulus changes\text{hash modulus changes}

Moved keys after modulus change

The old modulus has 3 partitions and the new modulus has 4. The compiled moved-key count is 5.

old partitions=3,new partitions=4,moved=5\text{old partitions}=3,\quad \text{new partitions}=4,\quad \text{moved}=5

Range and hash sharding are exact routing functions on tiny pinned key sets; real sharding adds consistent hashing, skew, hot partitions, and rebalancing cost, which are empirical and operational concerns beyond this model - no product claims.

Hash rebalance - moved: 3,4,5,6,7; stayed: 0,1,2keyfromtostatus0P0P0stayed1P1P1stayed2P2P2stayed3P0P3moved4P1P0moved5P2P1moved6P0P2moved7P1P3moved

Summary

Hash rebalance is still exact: compare old remainder route with new remainder route for each key. Note: operational migration plans are outside this model.

old route versus new route\text{old route versus new route}