44 lines
2.5 KiB
Markdown
44 lines
2.5 KiB
Markdown
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# Epoch
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The main purpose of the `epoch` in `frostfs` environment is to manipulate `netmap`.
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Each new epoch, `ir` service trigger revision content of the `netmap` by adding or removing nodes to or from it.
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`node` service trigger few internal processes each new epoch - for example, running GC.
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Epoch also used in an object lifecycle.
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At the startup, `ir` service initializes an epoch timer which handles new epoch tick.
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Epoch timer is a block timer - which means that this timer ticks each block or set of blocks.
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The epoch duration stores in the configurable parameter `EpochDuration` in the blockchain.
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It is possible to get it via `frostfs-adm`:
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```shell
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> frostfs-adm morph dump-config -c config.yml -r http://morph-chain.frostfs.devenv:30333
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...
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EpochDuration: 240 (int)
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...
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>
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```
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Once epoch timer ticks, `ir` service call method [NewEpoch](https://git.frostfs.info/TrueCloudLab/frostfs-contract/src/commit/a1b61d3949581f4d65b0d32a33d98ba9c193dc2a/netmap/netmap_contract.go#L238)
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of the `netmap` contract. Each `ir` instance can do this at the same time, but it is not an issue,
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because multiple call of this method with the same set of parameters will give us the same result.
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Utility `frostfs-adm` have a command to trigger new epoch:
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```shell
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> frostfs-adm morph force-new-epoch -c config.yml -r http://morph-chain.frostfs.devenv:30333
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```
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Command goes directly to the `netmap` contract and call method `NewEpoch`.
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Method checks alphabet witness and stores candidates nodes which are not in the `OFFLINE` state as a current netmap.
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Then executes method `NewEpoch` in `balance` and `container` contracts.
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At the end it produces notification `NewEpoch` which is handled by `node` and `ir` services.
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`ir` handler for `NewEpoch` updates internal state of the netmap, if it is necessary, updates state of the nodes or
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marks for exclusion from netmap in the blockchain.
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`node` handler for `NewEpoch` executes method `addPeer` of the `netmap` contract.
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This method do nothing, but produces notification which handled by `ir` service.
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`ir` in handler for `AddPeer` may update node state in the netmap if it is necessary.
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At the startup, node bootstraps with state `ONLINE`. From the online state, it is possible to move to `MAINTENANCE` or `OFFLINE`.
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Node moved to `OFFLINE` state automatically, when there is no bootstrap request from it for a number of epochs.
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This number stored in the `ir` config `netmap_cleaner.threshold`.
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From `OFFLINE` state node, once it bootstrapped, moves to `ONLINE`.
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`MAINTENANCE` state persists even if node rebooted or unavailable for a few epochs.
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