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58 lines
2.6 KiB
Markdown
58 lines
2.6 KiB
Markdown
---
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order: 10
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---
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# Block Sync
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*Formerly known as Fast Sync*
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In a proof of work blockchain, syncing with the chain is the same
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process as staying up-to-date with the consensus: download blocks, and
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look for the one with the most total work. In proof-of-stake, the
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consensus process is more complex, as it involves rounds of
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communication between the nodes to determine what block should be
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committed next. Using this process to sync up with the blockchain from
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scratch can take a very long time. It's much faster to just download
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blocks and check the merkle tree of validators than to run the real-time
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consensus gossip protocol.
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## Using Block Sync
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To support faster syncing, Tendermint offers a `fast-sync` mode, which
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is enabled by default, and can be toggled in the `config.toml` or via
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`--fast_sync=false`.
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In this mode, the Tendermint daemon will sync hundreds of times faster
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than if it used the real-time consensus process. Once caught up, the
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daemon will switch out of Block Sync and into the normal consensus mode.
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After running for some time, the node is considered `caught up` if it
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has at least one peer and it's height is at least as high as the max
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reported peer height. See [the IsCaughtUp
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method](https://github.com/tendermint/tendermint/blob/b467515719e686e4678e6da4e102f32a491b85a0/blockchain/pool.go#L128).
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Note: There are two versions of Block Sync. We recommend using v0 as v2 is still in beta.
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If you would like to use a different version you can do so by changing the version in the `config.toml`:
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```toml
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#######################################################
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### Block Sync Configuration Connections ###
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#######################################################
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[fastsync]
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# Block Sync version to use:
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# 1) "v0" (default) - the legacy Block Sync implementation
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# 2) "v2" - complete redesign of v0, optimized for testability & readability
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version = "v0"
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```
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If we're lagging sufficiently, we should go back to block syncing, but
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this is an [open issue](https://github.com/tendermint/tendermint/issues/129).
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## The Block Sync event
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When the tendermint blockchain core launches, it might switch to the `block-sync`
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mode to catch up the states to the current network best height. the core will emits
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a fast-sync event to expose the current status and the sync height. Once it catched
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the network best height, it will switches to the state sync mechanism and then emit
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another event for exposing the fast-sync `complete` status and the state `height`.
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The user can query the events by subscribing `EventQueryBlockSyncStatus`
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Please check [types](https://pkg.go.dev/github.com/tendermint/tendermint/types?utm_source=godoc#pkg-constants) for the details. |