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- # WAL
-
- Consensus module writes every message to the WAL (write-ahead log).
-
- It also issues fsync syscall through
- [File#Sync](https://golang.org/pkg/os/#File.Sync) for messages signed by this
- node (to prevent double signing).
-
- Under the hood, it uses
- [autofile.Group](https://godoc.org/github.com/tendermint/tmlibs/autofile#Group),
- which rotates files when those get too big (> 10MB).
-
- The total maximum size is 1GB. We only need the latest block and the block before it,
- but if the former is dragging on across many rounds, we want all those rounds.
-
- ## Replay
-
- Consensus module will replay all the messages of the last height written to WAL
- before a crash (if such occurs).
-
- The private validator may try to sign messages during replay because it runs
- somewhat autonomously and does not know about replay process.
-
- For example, if we got all the way to precommit in the WAL and then crash,
- after we replay the proposal message, the private validator will try to sign a
- prevote. But it will fail. That's ok because we’ll see the prevote later in the
- WAL. Then it will go to precommit, and that time it will work because the
- private validator contains the `LastSignBytes` and then we’ll replay the
- precommit from the WAL.
-
- Make sure to read about [WAL corruption](../../tendermint-core/running-in-production.md#wal-corruption)
- and recovery strategies.
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