LettuceConnectionProvider getConnection hang forever

[heoYH]

We use spring-data-redis and lettuce to access the redis cluster.

I don't know the cause, but there was a problem that the connection could not be initialization complete
As a result, sharedConnection could not be inited and fell into a waiting state forever
And after that, all requests became blocking.

###thread dump

"lettuce-epollEventLoop-5-6" tid=0x3f native=false suspended=false
   java.lang.Thread.State: WAITING
	at jdk.internal.misc.Unsafe.park(java.base@11.0.9.1/Native Method)
	at java.util.concurrent.locks.LockSupport.park(java.base@11.0.9.1/LockSupport.java:194)
	at java.util.concurrent.CompletableFuture$Signaller.block(java.base@11.0.9.1/CompletableFuture.java:1796)
	at java.util.concurrent.ForkJoinPool.managedBlock(java.base@11.0.9.1/ForkJoinPool.java:3128)
	at java.util.concurrent.CompletableFuture.waitingGet(java.base@11.0.9.1/CompletableFuture.java:1823)
	at java.util.concurrent.CompletableFuture.get(java.base@11.0.9.1/CompletableFuture.java:1998)
	at io.lettuce.core.cluster.RedisClusterClient.get(RedisClusterClient.java:937)
	at io.lettuce.core.cluster.RedisClusterClient.getPartitions(RedisClusterClient.java:329)
	at org.springframework.data.redis.connection.lettuce.ClusterConnectionProvider.getConnectionAsync(ClusterConnectionProvider.java:92)
	at org.springframework.data.redis.connection.lettuce.ClusterConnectionProvider.getConnectionAsync(ClusterConnectionProvider.java:40)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionProvider.getConnection(LettuceConnectionProvider.java:53)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory$ExceptionTranslatingConnectionProvider.getConnection(LettuceConnectionFactory.java:1527)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory$SharedConnection.getNativeConnection(LettuceConnectionFactory.java:1315)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory$SharedConnection.getConnection(LettuceConnectionFactory.java:1298)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getSharedReactiveConnection(LettuceConnectionFactory.java:1049)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getReactiveClusterConnection(LettuceConnectionFactory.java:481)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getReactiveConnection(LettuceConnectionFactory.java:457)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getReactiveConnection(LettuceConnectionFactory.java:101)
	at org.springframework.data.redis.core.ReactiveRedisTemplate.lambda$doInConnection$0(ReactiveRedisTemplate.java:198)
	at org.springframework.data.redis.core.ReactiveRedisTemplate$$Lambda$1725/0x0000000100cadc40.get(Unknown Source)
	at reactor.core.publisher.MonoSupplier.call(MonoSupplier.java:85)

"lettuce-epollEventLoop-5-5" tid=0x3e native=false suspended=false
   java.lang.Thread.State: BLOCKED
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory$SharedConnection.getConnection(LettuceConnectionFactory.java:1297)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getSharedReactiveConnection(LettuceConnectionFactory.java:1049)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getReactiveClusterConnection(LettuceConnectionFactory.java:481)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getReactiveConnection(LettuceConnectionFactory.java:457)
	at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getReactiveConnection(LettuceConnectionFactory.java:101)
	at org.springframework.data.redis.core.ReactiveRedisTemplate.lambda$doInConnection$0(ReactiveRedisTemplate.java:198)
	at org.springframework.data.redis.core.ReactiveRedisTemplate$$Lambda$1725/0x0000000100cadc40.get(Unknown Source)
	at reactor.core.publisher.MonoSupplier.call(MonoSupplier.java:85)
	at reactor.core.publisher.FluxUsingWhen.subscribe(FluxUsingWhen.java:80)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:236)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onComplete(MonoIgnoreThen.java:203)
	at org.springframework.cloud.sleuth.instrument.reactor.ScopePassingSpanSubscriber.onComplete(ScopePassingSpanSubscriber.java:102)
	at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onComplete(FluxSwitchIfEmpty.java:84)
	at org.springframework.cloud.sleuth.instrument.reactor.ScopePassingSpanSubscriber.onComplete(ScopePassingSpanSubscriber.java:102)
	at reactor.core.publisher.MonoIgnoreElements$IgnoreElementsSubscriber.onComplete(MonoIgnoreElements.java:88)
	at reactor.core.publisher.MonoIgnoreElements$IgnoreElementsSubscriber.onComplete(MonoIgnoreElements.java:88)
	at reactor.core.publisher.Operators.complete(Operators.java:136)

We are looking for the cause of the connection failing to connect.
My guess is that getConnection should have a timeout.

spring-data-redis/src/main/java/org/springframework/data/redis/connection/lettuce/LettuceConnectionProvider.java

Line 53 in d2cae75

return LettuceFutureUtils.join(getConnectionAsync(connectionType));

spring-data-redis/src/main/java/org/springframework/data/redis/connection/lettuce/LettuceFutureUtils.java

Line 68 in d2cae75

return future.toCompletableFuture().join();

This is because it should not "hang" when sharedConnection init fails for various reasons.

[mp911de]

This is a known issue and we plan to address it. Meanwhile, you can enable eager connection initialization to initialize the connection early on.

[heoYH]

@mp911de
Could you please explain this issue if possible?
(I wonder what is causing the problem.)

[mp911de]

Sure. SharedConnection synchronizes access to a single shared connection to ensure that we create only a single connection. With one or more event loop threads being blocked, they wait both for completion. They cannot complete because they wait for each other and then you end up with a sort of dead lock.

[TomHaughton]

Any updates on this? I'm experiencing what I believe to be the same/similar problem and I'm unable to send any commands through the shared connection. I've tried enabling eager initialization to no avail.

[123jiehao]

@mp911de is there any configuration to avoid this BLOCKED? or only restart redis?

[remnov]

Proposed workaround works.

To enable eager connection:
public void setEagerInitialization(boolean eagerInitialization)
have to be set to true before afterPropertiesSet()

Example:

LettuceConnectionFactory connectionFactory = new LettuceConnectionFactory(redisConfig, clientConfig);
connectionFactory.setEagerInitialization(true);
connectionFactory.afterPropertiesSet();

[roshansinghkande]

@mp911de Has there been a permanent fix for this? We are also facing this issue and in turn a lot of consequent issues.

[mp911de]

The fix is to enable eager connection initialization and not to use connection validation.