How is the ledger kept consistent among differnt peers in blockchain

Question

In a blockchain system like bitcoin, each peer (participate node) keeps a full copy of the ledger. A peer updates its copy of ledger when it receives and validates a newly arrived block. However, the peers are scattered around the globe, and the network latency among these peers varies a lot. Therefore, how the blockchain system guarantees that all the peers have finished updating their copies of ledger after a block has been propagated?

Answer 1

Bitcoin doesn't guarantee that all ledgers become updated at the same time, bitcoin blockchain provides you with consistent ledger following:

1. Proof-of-work to cut new block with set of transactions
2. Longest chain rule

Above guaranties you that if there no more than 51% of the network controlled by one group you will eventually see consistent ledger, e.g. given your ledger at block sequence number 1001 means all nodes in the network will see identical chain of blocks until 1001.

To your question bitcoins use random overlay network to distribute new blocks (pretty similar to gossip algorithm).