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clientv3: clarify "WithRequireLeader" for network partition #9872

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Jun 20, 2018
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clientv3: clarify "WithRequireLeader" for network partition #9872

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20 changes: 13 additions & 7 deletions clientv3/watch.go
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Original file line number Diff line number Diff line change
Expand Up @@ -50,13 +50,19 @@ type Watcher interface {
// and "WatchResponse" from this closed channel has zero events and nil "Err()".
// The context "ctx" MUST be canceled, as soon as watcher is no longer being used,
// to release the associated resources.
// If the context is "context.Background/TODO", returned "WatchChan" will not be closed
// and wait until events happen, except when server returns a non-recoverable error.
// For example, when context passed with "WithRequireLeader" and the connected server
// has no leader, error "etcdserver: no leader" is returned, and then "WatchChan" is
// closed with non-nil "Err()".
// Otherwise, as long as the context has not been canceled or timed out, watch will
// retry on other recoverable errors forever until reconnected.
//
// If the context is "context.Background/TODO", returned "WatchChan" will
// not be closed and block until event is triggered, except when server
// returns a non-recoverable error (e.g. ErrCompacted).
// For example, when context passed with "WithRequireLeader" and the
// connected server has no leader (e.g. due to network partition),
// error "etcdserver: no leader" (ErrNoLeader) will be returned,
// and then "WatchChan" is closed with non-nil "Err()".
// In order to prevent a watch stream being stuck in a partitioned node,
// make sure to wrap context with "WithRequireLeader".
//
// Otherwise, as long as the context has not been canceled or timed out,
// watch will retry on other recoverable errors forever until reconnected.
//
// TODO: explicitly set context error in the last "WatchResponse" message and close channel?
// Currently, client contexts are overwritten with "valCtx" that never closes.
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