All Superinterfaces:

java.lang.AutoCloseable, ReaderGroupNotificationListener
```
public interface ReaderGroup
extends ReaderGroupNotificationListener, java.lang.AutoCloseable
```
A reader group is a collection of readers that collectively read all the events in the stream. The events are distributed among the readers in the group such that each event goes to only one reader. The readers in the group may change over time. Readers are added to the group by calling EventStreamClientFactory.createReader(String, String, Serializer, ReaderConfig) and are removed by calling readerOffline(String, Position)

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`close()`	Closes the reader group, freeing any resources associated with it.
`java.util.concurrent.CompletableFuture<java.util.Map<Stream,StreamCut>>`	`generateStreamCuts(java.util.concurrent.ScheduledExecutorService backgroundExecutor)`	Generates a `StreamCut` after co-ordinating with all the readers using `StateSynchronizer`.
`java.lang.String`	`getGroupName()`	Returns the name of the group.
`ReaderGroupMetrics`	`getMetrics()`	Returns metrics for this reader group.
`java.util.Set<java.lang.String>`	`getOnlineReaders()`	Returns a set of readerIds for the readers that are considered to be online by the group.
`ReaderSegmentDistribution`	`getReaderSegmentDistribution()`	Returns current distribution of number of segments assigned to each reader in the reader group.
`java.lang.String`	`getScope()`	Returns the scope of the stream which the group is associated with.
`java.util.Map<Stream,StreamCut>`	`getStreamCuts()`	Returns a `StreamCut` for each stream that this reader group is reading from.
`java.util.Set<java.lang.String>`	`getStreamNames()`	Returns the set of scoped stream names which was used to configure this group.
`java.util.concurrent.CompletableFuture<Checkpoint>`	`initiateCheckpoint(java.lang.String checkpointName, java.util.concurrent.ScheduledExecutorService backgroundExecutor)`	Initiate a checkpoint.
`void`	`readerOffline(java.lang.String readerId, Position lastPosition)`	Invoked when a reader that was added to the group is no longer consuming events.
`void`	`resetReaderGroup(ReaderGroupConfig config)`	Reset a reader group with the provided `ReaderGroupConfig`.
`void`	`updateRetentionStreamCut(java.util.Map<Stream,StreamCut> streamCuts)`	Update Retention Stream-Cut for Streams in this Reader Group.

Methods inherited from interface io.pravega.client.stream.notifications.ReaderGroupNotificationListener
getEndOfDataNotifier, getSegmentNotifier

- Method Detail
  - getMetrics
```
ReaderGroupMetrics getMetrics()
```
    Returns metrics for this reader group.
    
    Returns:
    
    a ReaderGroupMetrics object for this reader group.
  - getScope
```
java.lang.String getScope()
```
    Returns the scope of the stream which the group is associated with.
    
    Returns:
    
    A scope string
  - getGroupName
```
java.lang.String getGroupName()
```
    Returns the name of the group.
    
    Returns:
    
    Reader group name
  - initiateCheckpoint
```
java.util.concurrent.CompletableFuture<Checkpoint> initiateCheckpoint(java.lang.String checkpointName,
                                                                      java.util.concurrent.ScheduledExecutorService backgroundExecutor)
```
    Initiate a checkpoint. This causes all readers in the group to receive a special EventRead that contains the provided checkpoint name. This can be used to provide an indication to them that they should persist their state. Once all of the readers have received the notification and resumed reading the future will return a Checkpoint object which contains the StreamCut of the reader group at the time they received the checkpoint. This can be used to reset the group to this point in the stream by calling resetReaderGroup(ReaderGroupConfig) if the checkpoint fails or the result cannot be obtained an exception will be set on the future. This method can be called and a new checkpoint can be initiated while another is still in progress if they have different names. If this method is is called again before the checkpoint has completed with the same name the future returned to the second caller will refer to the same checkpoint object as the first.
    
    Parameters:
    
    checkpointName - The name of the checkpoint (For identification purposes)
    
    backgroundExecutor - A threadPool that can be used to poll for the completion of the checkpoint.
    
    Returns:
    
    A future Checkpoint object that can be used to restore the reader group to this position.
  - resetReaderGroup
```
void resetReaderGroup(ReaderGroupConfig config)
```
    Reset a reader group with the provided ReaderGroupConfig.
    - The stream(s) that are part of the reader group can be specified using ReaderGroupConfig.ReaderGroupConfigBuilder.stream(String), ReaderGroupConfig.ReaderGroupConfigBuilder.stream(String, StreamCut) and ReaderGroupConfig.ReaderGroupConfigBuilder.stream(String, StreamCut, StreamCut).
    
    - To reset a reader group to a given checkpoint use ReaderGroupConfig.ReaderGroupConfigBuilder.startFromCheckpoint(Checkpoint) api.
    
    - To reset a reader group to a given StreamCut use ReaderGroupConfig.ReaderGroupConfigBuilder.startFromStreamCuts(Map).
    All existing readers will have to call EventStreamClientFactory.createReader(String, String, Serializer, ReaderConfig). If they continue to read events they will eventually encounter an ReinitializationRequiredException .
    
    Parameters:
    
    config - The new configuration for the ReaderGroup.
  - readerOffline
```
void readerOffline(java.lang.String readerId,
                   Position lastPosition)
```
    Invoked when a reader that was added to the group is no longer consuming events. This will cause the events that were going to that reader to be redistributed among the other readers. Events after the lastPosition provided will be (re)read by other readers in the ReaderGroup. Note that this method is automatically invoked by EventStreamReader.close()
    
    Parameters:
    
    readerId - The id of the reader that is offline.
    
    lastPosition - The position of the last event that was successfully processed by the reader.
  - getOnlineReaders
```
java.util.Set<java.lang.String> getOnlineReaders()
```
    Returns a set of readerIds for the readers that are considered to be online by the group. i.e. EventStreamClientFactory.createReader(String, String, Serializer, ReaderConfig) was called but readerOffline(String, Position) was not called subsequently.
    
    Returns:
    
    Set of active reader IDs of the group
  - getStreamNames
```
java.util.Set<java.lang.String> getStreamNames()
```
    Returns the set of scoped stream names which was used to configure this group.
    
    Returns:
    
    Set of streams for this group.
  - getStreamCuts
```
java.util.Map<Stream,StreamCut> getStreamCuts()
```
    Returns a StreamCut for each stream that this reader group is reading from. The stream cut corresponds to the last checkpointed read offsets of the readers, and it can be used by the application as reference to such a position. A more precise StreamCut, with the latest read offsets can be obtained using generateStreamCuts(ScheduledExecutorService) API.
    
    Returns:
    
    Map of streams that this group is reading from to the corresponding cuts.
  - generateStreamCuts
```
@Beta
java.util.concurrent.CompletableFuture<java.util.Map<Stream,StreamCut>> generateStreamCuts(java.util.concurrent.ScheduledExecutorService backgroundExecutor)
```
    Generates a StreamCut after co-ordinating with all the readers using StateSynchronizer. A StreamCut is generated by using the latest segment read offsets returned by the readers along with unassigned segments (if any). The configuration ReaderGroupConfig.groupRefreshTimeMillis decides the maximum delay by which the readers return the latest read offsets of their assigned segments.
    The StreamCut generated by this API can be used by the application as a reference to a position in the stream. This is guaranteed to be greater than or equal to the position of the readers at the point of invocation of the API. The StreamCuts generated can be used to perform bounded processing of the Stream by configuring a ReaderGroup with a ReaderGroupConfig where the StreamCuts are specified as the lower bound and/or upper bounds using the apis ReaderGroupConfig.ReaderGroupConfigBuilder.stream(Stream, StreamCut, StreamCut) or ReaderGroupConfig.ReaderGroupConfigBuilder.stream(Stream, StreamCut) or ReaderGroupConfig.ReaderGroupConfigBuilder.startFromStreamCuts(Map).
    Note: Generating a precise StreamCut, for example a StreamCut pointing to end of Q1 across all segments, is difficult as it depends on the configuration ReaderGroupConfig.groupRefreshTimeMillis which decides the duration by which all the readers running on different machines/ processes respond with their latest read offsets. Hence, the StreamCut would point to a position in the Stream which might include events from Q2. The application thus would need to filter out such additional events.
    
    Parameters:
    
    backgroundExecutor - A thread pool that will be used to poll if the positions from all the readers have been fetched.
    
    Returns:
    
    A future to a Map of Streams (that this group is reading from) to its corresponding cuts.
  - updateRetentionStreamCut
```
void updateRetentionStreamCut(java.util.Map<Stream,StreamCut> streamCuts)
```
    Update Retention Stream-Cut for Streams in this Reader Group. See ReaderGroupConfig.StreamDataRetention.MANUAL_RELEASE_AT_USER_STREAMCUT
    
    Parameters:
    
    streamCuts - A Map with a Stream-Cut for each Stream. StreamCut indicates position in the Stream till which data has been consumed and can be deleted.
  - getReaderSegmentDistribution
```
ReaderSegmentDistribution getReaderSegmentDistribution()
```
    Returns current distribution of number of segments assigned to each reader in the reader group.
    
    Returns:
    
    an instance of ReaderSegmentDistribution which describes the distribution of segments to readers including unassigned segments.
  - close
```
void close()
```
    Closes the reader group, freeing any resources associated with it.
    
    Specified by:
    
    close in interface java.lang.AutoCloseable

Interface ReaderGroup

Method Summary

Methods inherited from interface io.pravega.client.stream.notifications.ReaderGroupNotificationListener

Method Detail

getMetrics

getScope

getGroupName

initiateCheckpoint

resetReaderGroup

readerOffline

getOnlineReaders

getStreamNames

getStreamCuts

generateStreamCuts

updateRetentionStreamCut

getReaderSegmentDistribution

close