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Merge pull request #4049 from xiang90/raft_comment

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raft: rework comment for advance interface
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Xiang Li 2016-02-13 10:22:18 -08:00
commit 3d73e72bf6
1 changed files with 28 additions and 2 deletions
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30
raft/node.go
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@ -114,11 +114,37 @@ type Node interface {
ProposeConfChange(ctx context.Context, cc pb.ConfChange) error
// Step advances the state machine using the given message. ctx.Err() will be returned, if any.
Step(ctx context.Context, msg pb.Message) error
// Ready returns a channel that returns the current point-in-time state.
// Users of the Node must call Advance after applying the state returned by Ready.
// Users of the Node must call Advance after retrieving the state returned by Ready.
//
// NOTE: No committed entries from the next Ready may be applied until all committed entries
// and snapshots from the previous one have finished.
Ready() <-chan Ready
// Advance notifies the Node that the application has applied and saved progress up to the last Ready.
// Advance notifies the Node that the application has saved progress up to the last Ready.
// It prepares the node to return the next available Ready.
//
// The application should generally call Advance after it applies the entries in last Ready.
//
// However, as an optimization, the application may call Advance while it is applying the
// commands. For example. when the last Ready contains a snapshot, the application might take
// a long time to apply the snapshot data. To continue receiving Ready without blocking raft
// progress, it can call Advance before finish applying the last ready. To make this optimization
// work safely, when the application receives a Ready with softState.RaftState equal to Candidate
// it MUST apply all pending configuration changes if there is any.
//
// Here is a simple solution that waiting for ALL pending entries to get applied.
// ```
// ...
// rd := <-n.Ready()
// go apply(rd.CommittedEntries) // optimization to apply asynchronously in FIFO order.
// if rd.SoftState.RaftState == StateCandidate {
// waitAllApplied()
// }
// n.Advance()
// ...
//```
Advance()
// ApplyConfChange applies config change to the local node.
// Returns an opaque ConfState protobuf which must be recorded