Package org.apache.druid.metadata.segment.cache

Class HeapMemorySegmentMetadataCache

java.lang.Object

org.apache.druid.metadata.segment.cache.HeapMemorySegmentMetadataCache

All Implemented Interfaces:

SegmentMetadataCache

@ThreadSafe
public class HeapMemorySegmentMetadataCache
extends Object
implements SegmentMetadataCache

In-memory implementation of SegmentMetadataCache.

Only used segments (excluding num_rows and schema_fingerprint) and pending segments are cached. Unused segments are not cached.

Non-leader Overlords also keep polling the metadata store to keep the cache up-to-date in case leadership changes.

For cache usage modes, see SegmentMetadataCache.UsageMode.

The map datasourceToSegmentCache contains the cache for each datasource. If the cache for a datasource is empty, the sync thread removes it from the map.

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.druid.metadata.segment.cache.SegmentMetadataCache

SegmentMetadataCache.Action<T>, SegmentMetadataCache.UsageMode

Constructor Summary

Constructors

Constructor	Description
HeapMemorySegmentMetadataCache(com.fasterxml.jackson.databind.ObjectMapper jsonMapper, com.google.common.base.Supplier<SegmentsMetadataManagerConfig> config, com.google.common.base.Supplier<MetadataStorageTablesConfig> tablesConfig, SegmentSchemaCache segmentSchemaCache, SQLMetadataConnector connector, ScheduledExecutorFactory executorFactory, ServiceEmitter emitter)

Method Summary

Modifier and Type	Method	Description
void	awaitNextSync(long timeoutMillis)	Waits until the cache finishes the next sync with the metadata store or until the timeout elapses, whichever is sooner.
void	becomeLeader()	Refreshes the cache once the service is elected leader.
DataSourcesSnapshot	getDataSourcesSnapshot()
boolean	isEnabled()
boolean	isSyncedForRead()
<T> T	readCacheForDataSource(String dataSource, SegmentMetadataCache.Action<T> readAction)	Performs a thread-safe read action on the cache for the given datasource.
void	start()	Starts the cache on service start.
void	stop()	Stops the cache on service stop.
void	stopBeingLeader()	Notifies the cache that the service has lost leadership.
<T> T	writeCacheForDataSource(String dataSource, SegmentMetadataCache.Action<T> writeAction)	Performs a thread-safe write action on the cache for the given datasource.

Methods inherited from class java.lang.Object

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

Constructor Details

HeapMemorySegmentMetadataCache

@Inject
public HeapMemorySegmentMetadataCache(com.fasterxml.jackson.databind.ObjectMapper jsonMapper,
 com.google.common.base.Supplier<SegmentsMetadataManagerConfig> config,
 com.google.common.base.Supplier<MetadataStorageTablesConfig> tablesConfig,
 SegmentSchemaCache segmentSchemaCache,
 SQLMetadataConnector connector,
 ScheduledExecutorFactory executorFactory,
 ServiceEmitter emitter)

Method Details

start

public void start()

Description copied from interface: SegmentMetadataCache

Starts the cache on service start.

Specified by:

start in interface SegmentMetadataCache

stop

public void stop()

Description copied from interface: SegmentMetadataCache

Stops the cache on service stop.

Specified by:

stop in interface SegmentMetadataCache

becomeLeader

public void becomeLeader()

Description copied from interface: SegmentMetadataCache

Refreshes the cache once the service is elected leader.

Specified by:

becomeLeader in interface SegmentMetadataCache

stopBeingLeader

public void stopBeingLeader()

Description copied from interface: SegmentMetadataCache

Notifies the cache that the service has lost leadership.

Specified by:

stopBeingLeader in interface SegmentMetadataCache

isEnabled

public boolean isEnabled()

Specified by:

isEnabled in interface SegmentMetadataCache

Returns:

true if the cache is enabled

isSyncedForRead

public boolean isSyncedForRead()

Specified by:

isSyncedForRead in interface SegmentMetadataCache

Returns:

true if the cache is enabled and synced with the metadata store. Reads can be done from the cache only if it is synced but writes can happen even before the sync has finished.

getDataSourcesSnapshot

public DataSourcesSnapshot getDataSourcesSnapshot()

Specified by:

getDataSourcesSnapshot in interface SegmentMetadataCache

Returns:

Latest snapshot of the datasources with all their used segments.

awaitNextSync

public void awaitNextSync(long timeoutMillis)

Description copied from interface: SegmentMetadataCache

Waits until the cache finishes the next sync with the metadata store or until the timeout elapses, whichever is sooner.

Specified by:

awaitNextSync in interface SegmentMetadataCache

readCacheForDataSource

public <T> T readCacheForDataSource(String dataSource,
 SegmentMetadataCache.Action<T> readAction)

Description copied from interface: SegmentMetadataCache

Performs a thread-safe read action on the cache for the given datasource. Read actions can be concurrent with other reads but are mutually exclusive from other write actions on the same datasource.

Specified by:

readCacheForDataSource in interface SegmentMetadataCache

writeCacheForDataSource

public <T> T writeCacheForDataSource(String dataSource,
 SegmentMetadataCache.Action<T> writeAction)

Description copied from interface: SegmentMetadataCache

Performs a thread-safe write action on the cache for the given datasource. Write actions are mutually exclusive from other writes or reads on the same datasource.

Specified by:

writeCacheForDataSource in interface SegmentMetadataCache