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- ---
- order: 6
- ---
-
- # Fast Sync
-
- In a proof of work blockchain, syncing with the chain is the same
- process as staying up-to-date with the consensus: download blocks, and
- look for the one with the most total work. In proof-of-stake, the
- consensus process is more complex, as it involves rounds of
- communication between the nodes to determine what block should be
- committed next. Using this process to sync up with the blockchain from
- scratch can take a very long time. It's much faster to just download
- blocks and check the merkle tree of validators than to run the real-time
- consensus gossip protocol.
-
- ## Using Fast Sync
-
- To support faster syncing, tendermint offers a `fast-sync` mode, which
- is enabled by default, and can be toggled in the `config.toml` or via
- `--fast_sync=false`.
-
- In this mode, the tendermint daemon will sync hundreds of times faster
- than if it used the real-time consensus process. Once caught up, the
- daemon will switch out of fast sync and into the normal consensus mode.
- After running for some time, the node is considered `caught up` if it
- has at least one peer and it's height is at least as high as the max
- reported peer height. See [the IsCaughtUp
- method](https://github.com/tendermint/tendermint/blob/b467515719e686e4678e6da4e102f32a491b85a0/blockchain/pool.go#L128).
-
- If we're lagging sufficiently, we should go back to fast syncing, but
- this is an [open issue](https://github.com/tendermint/tendermint/issues/129).
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