java.lang.Object
- org.apache.solr.cloud.Overseer

All Implemented Interfaces:

Closeable, AutoCloseable, org.apache.solr.common.SolrCloseable
```
public class Overseer
extends Object
implements org.apache.solr.common.SolrCloseable
```
Cluster leader. Responsible for processing state updates, node assignments, creating/deleting collections, shards, replicas and setting various properties.
The Overseer is a single elected node in the SolrCloud cluster that is in charge of interactions with ZooKeeper that require global synchronization.
The Overseer deals with:
- Cluster State updates, i.e. updating Collections' state.json files in ZooKeeper, see Overseer.ClusterStateUpdater,
- Collection API implementation, see OverseerCollectionConfigSetProcessor and OverseerCollectionMessageHandler (and the example below),
- Updating Config Sets, see OverseerCollectionConfigSetProcessor and OverseerConfigSetMessageHandler,
The nodes in the cluster communicate with the Overseer over queues implemented in ZooKeeper. There are essentially two queues:
1. The state update queue, through which nodes request the Overseer to update the state.json file of a Collection in ZooKeeper. This queue is in Zookeeper at /overseer/queue,
2. A queue shared between Collection API and Config Set API requests. This queue is in Zookeeper at /overseer/collection-queue-work.
An example of the steps involved in the Overseer processing a Collection creation API call:
1. Client uses the Collection API with CREATE action and reaches a node of the cluster,
2. The node (via CollectionsHandler) enqueues the request into the /overseer/collection-queue-work queue in ZooKeepeer,
3. The OverseerCollectionConfigSetProcessor running on the Overseer node dequeues the message and using an executor service with a maximum pool size of OverseerTaskProcessor.MAX_PARALLEL_TASKS hands it for processing to OverseerCollectionMessageHandler,
4. Command CreateCollectionCmd then executes and does:
  1. Update some state directly in ZooKeeper (creating collection znode),
  2. Compute replica placement on available nodes in the cluster,
  3. Enqueue a state change request for creating the state.json file for the collection in ZooKeeper. This is done by enqueuing a message in /overseer/queue,
  4. The command then waits for the update to be seen in ZooKeeper...
5. The Overseer.ClusterStateUpdater (also running on the Overseer node) dequeues the state change message and creates the state.json file in ZooKeeper for the Collection. All the work of the cluster state updater (creations, updates, deletes) is done sequentially for the whole cluster by a single thread.
6. The CreateCollectionCmd sees the state change in ZooKeeper and:
  1. Builds and sends requests to each node to create the appropriate cores for all the replicas of all shards of the collection. Nodes create the replicas and set them to Replica.State.ACTIVE.
7. The collection creation command has succeeded from the Overseer perspective,
8. CollectionsHandler checks the replicas in Zookeeper and verifies they are all Replica.State.ACTIVE,
9. The client receives a success return.

Nested Class Summary

Nested Classes
Modifier and Type Class Description

static interface Overseer.Message

static class Overseer.OverseerThread

Field Summary

Fields
Modifier and Type	Field	Description
`static int`	`NUM_RESPONSES_TO_STORE`
`static String`	`OVERSEER_ELECT`
`static String`	`QUEUE_OPERATION`
`static int`	`STATE_UPDATE_BATCH_SIZE`
`static int`	`STATE_UPDATE_DELAY`
`static int`	`STATE_UPDATE_MAX_QUEUE`

Constructor Summary

Constructors
Constructor	Description
`Overseer(HttpShardHandler shardHandler, UpdateShardHandler updateShardHandler, String adminPath, org.apache.solr.common.cloud.ZkStateReader reader, ZkController zkController, CloudConfig config)`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`close()`
`CoreContainer`	`getCoreContainer()`
`DistributedClusterStateUpdater`	`getDistributedClusterStateUpdater()`
`org.apache.solr.client.solrj.cloud.SolrCloudManager`	`getSolrCloudManager()`
`Stats`	`getStats()`	Stop `ClusterSingleton` plugins when we lose leadership.
`Overseer.OverseerThread`	`getUpdaterThread()`	For tests.
`org.apache.solr.common.cloud.ZkStateReader`	`getZkStateReader()`
`boolean`	`isClosed()`
`void`	`offerStateUpdate(byte[] data)`
`void`	`offerStateUpdate(org.apache.solr.common.MapWriter mw)`
`void`	`sendQuitToOverseer(String overseerId)`	This method enqueues a QUIT message to the overseer of given id.
`void`	`start(String id)`
`void`	`submit(Overseer.Message message)`	Submit an intra-process message which will be picked up and executed when `Overseer.ClusterStateUpdater`'s loop runs next time
`void`	`systemCollectionCompatCheck(BiConsumer<String,Object> consumer)`

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

QUEUE_OPERATION

public static final String QUEUE_OPERATION

See Also:: Constant Field Values

STATE_UPDATE_DELAY

public static final int STATE_UPDATE_DELAY

STATE_UPDATE_BATCH_SIZE

public static final int STATE_UPDATE_BATCH_SIZE

STATE_UPDATE_MAX_QUEUE

public static final int STATE_UPDATE_MAX_QUEUE

NUM_RESPONSES_TO_STORE
```
public static final int NUM_RESPONSES_TO_STORE
```
See Also:

Constant Field Values

OVERSEER_ELECT

public static final String OVERSEER_ELECT

See Also:: Constant Field Values

Constructor Detail

Overseer

public Overseer(HttpShardHandler shardHandler,
                UpdateShardHandler updateShardHandler,
                String adminPath,
                org.apache.solr.common.cloud.ZkStateReader reader,
                ZkController zkController,
                CloudConfig config)
         throws org.apache.zookeeper.KeeperException,
                InterruptedException

Throws:: org.apache.zookeeper.KeeperException; InterruptedException

Method Detail
- start
```
public void start(String id)
```
- systemCollectionCompatCheck
```
public void systemCollectionCompatCheck(BiConsumer<String,Object> consumer)
```
- getStats
```
public Stats getStats()
```
  Stop ClusterSingleton plugins when we lose leadership.
- getCoreContainer
```
public CoreContainer getCoreContainer()
```
- getSolrCloudManager
```
public org.apache.solr.client.solrj.cloud.SolrCloudManager getSolrCloudManager()
```
- getDistributedClusterStateUpdater
```
public DistributedClusterStateUpdater getDistributedClusterStateUpdater()
```
- getUpdaterThread
```
public Overseer.OverseerThread getUpdaterThread()
```
  For tests.
  
  Returns:
  
  state updater thread
  
  NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.
- close
```
public void close()
```
  Specified by:
  
  close in interface AutoCloseable
  
  Specified by:
  
  close in interface Closeable
- isClosed
```
public boolean isClosed()
```
  Specified by:
  
  isClosed in interface org.apache.solr.common.SolrCloseable
- getZkStateReader
```
public org.apache.solr.common.cloud.ZkStateReader getZkStateReader()
```
- offerStateUpdate
```
public void offerStateUpdate(org.apache.solr.common.MapWriter mw)
                      throws org.apache.zookeeper.KeeperException,
                             InterruptedException
```
  Throws:
  
  org.apache.zookeeper.KeeperException
  
  InterruptedException
- offerStateUpdate
```
public void offerStateUpdate(byte[] data)
                      throws org.apache.zookeeper.KeeperException,
                             InterruptedException
```
  Throws:
  
  org.apache.zookeeper.KeeperException
  
  InterruptedException
- submit
```
public void submit(Overseer.Message message)
```
  Submit an intra-process message which will be picked up and executed when Overseer.ClusterStateUpdater's loop runs next time
- sendQuitToOverseer
```
public void sendQuitToOverseer(String overseerId)
                        throws org.apache.zookeeper.KeeperException,
                               InterruptedException
```
  This method enqueues a QUIT message to the overseer of given id. Effect is similar to building the message then calling offerStateUpdate(org.apache.solr.common.MapWriter) but this method can legitimately be called when cluster state update is distributed (and Overseer cluster state updater not really used) while offerStateUpdate(org.apache.solr.common.MapWriter) is not. Note that sending "QUIT" to overseer is not a cluster state update and was likely added to this queue because it was simpler.
  
  Throws:
  
  org.apache.zookeeper.KeeperException
  
  InterruptedException

Modifier and Type	Class	Description
`static interface`	`Overseer.Message`
`static class`	`Overseer.OverseerThread`

Class Overseer

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

QUEUE_OPERATION

STATE_UPDATE_DELAY

STATE_UPDATE_BATCH_SIZE

STATE_UPDATE_MAX_QUEUE

NUM_RESPONSES_TO_STORE

OVERSEER_ELECT

Constructor Detail

Overseer

Method Detail

start

systemCollectionCompatCheck

getStats

getCoreContainer

getSolrCloudManager

getDistributedClusterStateUpdater

getUpdaterThread

close

isClosed

getZkStateReader

offerStateUpdate

offerStateUpdate

submit

sendQuitToOverseer