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- ---
- order: 10
- ---
-
- # 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).
-
- Note: There are three versions of fast sync. We recommend using v0 as v2 is still in beta.
- If you would like to use a different version you can do so by changing the version in the `config.toml`:
-
- ```toml
- #######################################################
- ### Fast Sync Configuration Connections ###
- #######################################################
- [fastsync]
-
- # Fast Sync version to use:
- # 1) "v0" (default) - the legacy fast sync implementation
- # 2) "v2" - complete redesign of v0, optimized for testability & readability
- version = "v0"
- ```
-
- 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).
-
- ## The Fast Sync event
- When the tendermint blockchain core launches, it might switch to the `fast-sync`
- mode to catch up the states to the current network best height. the core will emits
- a fast-sync event to expose the current status and the sync height. Once it catched
- the network best height, it will switches to the state sync mechanism and then emit
- another event for exposing the fast-sync `complete` status and the state `height`.
-
- The user can query the events by subscribing `EventQueryFastSyncStatus`
- Please check [types](https://pkg.go.dev/github.com/tendermint/tendermint/types?utm_source=godoc#pkg-constants) for the details.
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