Package org.apache.flink.kubernetes.highavailability

Class KubernetesStateHandleStore<T extends Serializable>

java.lang.Object
org.apache.flink.kubernetes.highavailability.KubernetesStateHandleStore<T>
Type Parameters:
T - Type of the state we're storing.
All Implemented Interfaces:
org.apache.flink.runtime.persistence.StateHandleStore<T,org.apache.flink.runtime.persistence.StringResourceVersion>
public class KubernetesStateHandleStore<T extends Serializable> extends Object implements org.apache.flink.runtime.persistence.StateHandleStore<T,org.apache.flink.runtime.persistence.StringResourceVersion>
Class which stores state via the provided RetrievableStateStorageHelper and writes the returned state handle to ConfigMap.

Added state is persisted via RetrievableStateHandles, which in turn are written to ConfigMap. This level of indirection is necessary to keep the amount of data in ConfigMap small. ConfigMap is build for data less than 1MB whereas state can grow to multiple MBs and GBs.

This is a very different implementation with ZooKeeperStateHandleStore. Benefit from the FlinkKubeClient.checkAndUpdateConfigMap(java.lang.String, java.util.function.Function<org.apache.flink.kubernetes.kubeclient.resources.KubernetesConfigMap, java.util.Optional<org.apache.flink.kubernetes.kubeclient.resources.KubernetesConfigMap>>) transactional operation, we could guarantee that only the leader could update the store. Then we will completely get rid of the lock-and-release in Zookeeper implementation.

  • Nested Class Summary

    Nested classes/interfaces inherited from interface org.apache.flink.runtime.persistence.StateHandleStore

    org.apache.flink.runtime.persistence.StateHandleStore.AlreadyExistException, org.apache.flink.runtime.persistence.StateHandleStore.NotExistException

  • Constructor Summary

    Constructors
    Constructor
    Description
    KubernetesStateHandleStore(FlinkKubeClient kubeClient, String configMapName, org.apache.flink.runtime.persistence.RetrievableStateStorageHelper<T> storage, Predicate<String> configMapKeyFilter, String lockIdentity)
    Creates a KubernetesStateHandleStore.

  • Method Summary

    Modifier and Type
    Method
    Description
    org.apache.flink.runtime.state.RetrievableStateHandle<T>
    addAndLock(String key, T state)
    Creates a state handle, stores it in ConfigMap.
    void
    clearEntries()
    Remove all the filtered keys in the ConfigMap.
    org.apache.flink.runtime.persistence.StringResourceVersion
    exists(String key)
    Returns the resource version of the ConfigMap.
    List<org.apache.flink.api.java.tuple.Tuple2<org.apache.flink.runtime.state.RetrievableStateHandle<T>,String>>
    getAllAndLock()
    Gets all available state handles from Kubernetes.
    Collection<String>
    getAllHandles()
    Return a list of all valid keys for state handles.
    org.apache.flink.runtime.state.RetrievableStateHandle<T>
    getAndLock(String key)
    Gets the RetrievableStateHandle stored in the given ConfigMap.
    void
    release(String name)
     
    void
    releaseAll()
     
    boolean
    releaseAndTryRemove(String key)
    Remove the key in state config map.
    void
    replace(String key, org.apache.flink.runtime.persistence.StringResourceVersion resourceVersion, T state)
    Replaces a state handle in ConfigMap and discards the old state handle.
    String
    toString()
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

  • Constructor Details

    • KubernetesStateHandleStore

      public KubernetesStateHandleStore(FlinkKubeClient kubeClient, String configMapName, org.apache.flink.runtime.persistence.RetrievableStateStorageHelper<T> storage, Predicate<String> configMapKeyFilter, @Nullable String lockIdentity)
      Creates a KubernetesStateHandleStore.
      Parameters:
      kubeClient - The Kubernetes client.
      storage - To persist the actual state and whose returned state handle is then written to ConfigMap
      configMapName - ConfigMap to store the state handle store pointer
      configMapKeyFilter - filter to get the expected keys for state handle
      lockIdentity - lock identity of current HA service

  • Method Details

    • addAndLock

      public org.apache.flink.runtime.state.RetrievableStateHandle<T> addAndLock(String key, T state) throws org.apache.flink.runtime.persistence.PossibleInconsistentStateException, Exception
      Creates a state handle, stores it in ConfigMap. We could guarantee that only the leader could update the ConfigMap. Since “Get(check the leader)-and-Update(write back to the ConfigMap)” is a transactional operation.
      Specified by:
      addAndLock in interface org.apache.flink.runtime.persistence.StateHandleStore<T extends Serializable,org.apache.flink.runtime.persistence.StringResourceVersion>
      Parameters:
      key - Key in ConfigMap
      state - State to be added
      Throws:
      org.apache.flink.runtime.persistence.StateHandleStore.AlreadyExistException - if the name already exists
      org.apache.flink.runtime.persistence.PossibleInconsistentStateException - if the write-to-Kubernetes operation failed. This indicates that it's not clear whether the new state was successfully written to Kubernetes or not. No state was discarded. Proper error handling has to be applied on the caller's side.
      Exception - if persisting state or writing state handle failed

    • replace

      public void replace(String key, org.apache.flink.runtime.persistence.StringResourceVersion resourceVersion, T state) throws Exception
      Replaces a state handle in ConfigMap and discards the old state handle. Wo do not lock resource version and then replace in Kubernetes. Since the ConfigMap is periodically updated by leader, the resource version changes very fast. We use a "check-existence and update" transactional operation instead.
      Specified by:
      replace in interface org.apache.flink.runtime.persistence.StateHandleStore<T extends Serializable,org.apache.flink.runtime.persistence.StringResourceVersion>
      Parameters:
      key - Key in ConfigMap
      resourceVersion - resource version when checking existence via exists(java.lang.String).
      state - State to be added
      Throws:
      org.apache.flink.runtime.persistence.StateHandleStore.NotExistException - if the name does not exist
      org.apache.flink.runtime.persistence.PossibleInconsistentStateException - if a failure occurred during the update operation. It's unclear whether the operation actually succeeded or not. No state was discarded. The method's caller should handle this case properly.
      Exception - if persisting state or writing state handle failed

    • exists

      public org.apache.flink.runtime.persistence.StringResourceVersion exists(String key) throws Exception
      Returns the resource version of the ConfigMap.
      Specified by:
      exists in interface org.apache.flink.runtime.persistence.StateHandleStore<T extends Serializable,org.apache.flink.runtime.persistence.StringResourceVersion>
      Parameters:
      key - Key in ConfigMap
      Returns:
      resource version in StringResourceVersion format.
      Throws:
      Exception - if the check existence operation failed

    • getAndLock

      public org.apache.flink.runtime.state.RetrievableStateHandle<T> getAndLock(String key) throws Exception
      Gets the RetrievableStateHandle stored in the given ConfigMap.
      Specified by:
      getAndLock in interface org.apache.flink.runtime.persistence.StateHandleStore<T extends Serializable,org.apache.flink.runtime.persistence.StringResourceVersion>
      Parameters:
      key - Key in ConfigMap
      Returns:
      The retrieved state handle from the specified ConfigMap and key
      Throws:
      IOException - if the method failed to deserialize the stored state handle
      org.apache.flink.runtime.persistence.StateHandleStore.NotExistException - when the name does not exist
      Exception - if get state handle from ConfigMap failed

    • getAllAndLock

      public List<org.apache.flink.api.java.tuple.Tuple2<org.apache.flink.runtime.state.RetrievableStateHandle<T>,String>> getAllAndLock()
      Gets all available state handles from Kubernetes.
      Specified by:
      getAllAndLock in interface org.apache.flink.runtime.persistence.StateHandleStore<T extends Serializable,org.apache.flink.runtime.persistence.StringResourceVersion>
      Returns:
      All state handles from ConfigMap.

    • getAllHandles

      public Collection<String> getAllHandles() throws Exception
      Return a list of all valid keys for state handles.
      Specified by:
      getAllHandles in interface org.apache.flink.runtime.persistence.StateHandleStore<T extends Serializable,org.apache.flink.runtime.persistence.StringResourceVersion>
      Returns:
      List of valid state handle keys in Kubernetes ConfigMap
      Throws:
      Exception - if get state handle names from ConfigMap failed.

    • releaseAndTryRemove

      public boolean releaseAndTryRemove(String key) throws Exception
      Remove the key in state config map. As well as the state on external storage will be removed. It returns the RetrievableStateHandle stored under the given state node if any.
      Specified by:
      releaseAndTryRemove in interface org.apache.flink.runtime.persistence.StateHandleStore<T extends Serializable,org.apache.flink.runtime.persistence.StringResourceVersion>
      Parameters:
      key - Key to be removed from ConfigMap
      Returns:
      True if the state handle isn't listed anymore.
      Throws:
      Exception - if removing the key or discarding the state failed

    • clearEntries

      public void clearEntries() throws Exception
      Remove all the filtered keys in the ConfigMap.
      Specified by:
      clearEntries in interface org.apache.flink.runtime.persistence.StateHandleStore<T extends Serializable,org.apache.flink.runtime.persistence.StringResourceVersion>
      Throws:
      Exception - when removing the keys failed

    • release

      public void release(String name)
      Specified by:
      release in interface org.apache.flink.runtime.persistence.StateHandleStore<T extends Serializable,org.apache.flink.runtime.persistence.StringResourceVersion>

    • releaseAll

      public void releaseAll()
      Specified by:
      releaseAll in interface org.apache.flink.runtime.persistence.StateHandleStore<T extends Serializable,org.apache.flink.runtime.persistence.StringResourceVersion>

    • toString

      public String toString()
      Overrides:
      toString in class Object