Oddities and FAQs

Common questions and head scratchers.

Chain MMR

The chain MMR always lags behind the blockchain by one block because otherwise there would be a cyclic dependency between the chain MMR and the block hash:

• chain MMR contains each block's hash as a leaf
• block hash calculation includes the chain MMR's root

To work-around this the inclusion of a block hash in the chain MMR is delayed by one block. Or put differently, block N is responsible for inserting block N-1 into the chain MMR. This does not break blockchain linkage because the block header (and therefore hash) still includes the previous block's hash.