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Backoff on reestablishing watches when Unavailable errors are encountered #9840

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merged 1 commit into from
Jun 14, 2018
Merged

Backoff on reestablishing watches when Unavailable errors are encountered #9840

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14 changes: 14 additions & 0 deletions clientv3/client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -527,6 +527,20 @@ func isHaltErr(ctx context.Context, err error) bool {
return ev.Code() != codes.Unavailable && ev.Code() != codes.Internal
}

// isUnavailableErr returns true if the given error is an unavailable error
func isUnavailableErr(ctx context.Context, err error) bool {
if ctx != nil && ctx.Err() != nil {
return false
}
if err == nil {
return false
}
ev, _ := status.FromError(err)
// Unavailable codes mean the system will be right back.
// (e.g., can't connect, lost leader)
return ev.Code() == codes.Unavailable
}

func toErr(ctx context.Context, err error) error {
if err == nil {
return nil
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14 changes: 14 additions & 0 deletions clientv3/watch.go
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Original file line number Diff line number Diff line change
Expand Up @@ -830,10 +830,13 @@ func (w *watchGrpcStream) joinSubstreams() {
}
}

var maxBackoff = 100 * time.Millisecond

// openWatchClient retries opening a watch client until success or halt.
// manually retry in case "ws==nil && err==nil"
// TODO: remove FailFast=false
func (w *watchGrpcStream) openWatchClient() (ws pb.Watch_WatchClient, err error) {
backoff := time.Millisecond
for {
select {
case <-w.ctx.Done():
Expand All @@ -849,6 +852,17 @@ func (w *watchGrpcStream) openWatchClient() (ws pb.Watch_WatchClient, err error)
if isHaltErr(w.ctx, err) {
return nil, v3rpc.Error(err)
}
if isUnavailableErr(w.ctx, err) {
// retry, but backoff
if backoff < maxBackoff {
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abstract this out as a retry func with test?

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I'd probably save abstracting it for if we wanted to use this elsewhere... it sounded like there were more systemic retry improvements in progress, so it's possible this will get dropped in the future. I was mostly looking for something minimal we could pick to 3.2.x and 3.3.x streams to alleviate this specific hotloop.

// 25% backoff factor
backoff = backoff + backoff/4
if backoff > maxBackoff {
backoff = maxBackoff
}
}
time.Sleep(backoff)
}
}
return ws, nil
}
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