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core: round robin should ignore name resolution error for channel state change when there are READY subchannels (#7595) 

Round robin is keeping use of READY subchannels even if there is name resolution error. However, it moves Channel state to TRANSIENT_ERROR.

In hierarchical load balancers, the upstream LB policy may need to aggregate pickers from multiple downstream round_robin LB policy while filtering out non-ready subchannels. It cannot infer if the subchannel can be used just from the SubchannelPicker interface. It relies on the state that the round_robin intends to set channel to.

So the change is to match the readiness of the picker/subchannel with the state that round_robin tries to update. It will completely ignore name resolution error if there are READY subchannels.
This commit is contained in:
Chengyuan Zhang 2020-11-04 14:36:12 -08:00 committed by GitHub
parent 8020a735f9
commit 10dc41af74
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2 changed files with 4 additions and 5 deletions
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6
core/src/main/java/io/grpc/util/RoundRobinLoadBalancer.java
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@ -130,9 +130,9 @@ final class RoundRobinLoadBalancer extends LoadBalancer {
@Override @Override
public void handleNameResolutionError(Status error) { public void handleNameResolutionError(Status error) {
// ready pickers aren't affected by status changes if (currentState != READY) {
updateBalancingState(TRANSIENT_FAILURE, updateBalancingState(TRANSIENT_FAILURE, new EmptyPicker(error));
currentPicker instanceof ReadyPicker ? currentPicker : new EmptyPicker(error)); }
} }
private void processSubchannelState(Subchannel subchannel, ConnectivityStateInfo stateInfo) { private void processSubchannelState(Subchannel subchannel, ConnectivityStateInfo stateInfo) {

3
core/src/test/java/io/grpc/util/RoundRobinLoadBalancerTest.java
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@ -381,13 +381,12 @@ public class RoundRobinLoadBalancerTest {
loadBalancer.handleNameResolutionError(Status.NOT_FOUND.withDescription("nameResolutionError")); loadBalancer.handleNameResolutionError(Status.NOT_FOUND.withDescription("nameResolutionError"));
verify(mockHelper, times(3)).createSubchannel(any(CreateSubchannelArgs.class)); verify(mockHelper, times(3)).createSubchannel(any(CreateSubchannelArgs.class));
verify(mockHelper, times(3)) verify(mockHelper, times(2))
.updateBalancingState(stateCaptor.capture(), pickerCaptor.capture()); .updateBalancingState(stateCaptor.capture(), pickerCaptor.capture());
Iterator<ConnectivityState> stateIterator = stateCaptor.getAllValues().iterator(); Iterator<ConnectivityState> stateIterator = stateCaptor.getAllValues().iterator();
assertEquals(CONNECTING, stateIterator.next()); assertEquals(CONNECTING, stateIterator.next());
assertEquals(READY, stateIterator.next()); assertEquals(READY, stateIterator.next());
assertEquals(TRANSIENT_FAILURE, stateIterator.next());
LoadBalancer.PickResult pickResult = pickerCaptor.getValue().pickSubchannel(mockArgs); LoadBalancer.PickResult pickResult = pickerCaptor.getValue().pickSubchannel(mockArgs);
assertEquals(readySubchannel, pickResult.getSubchannel()); assertEquals(readySubchannel, pickResult.getSubchannel());