Package org.apache.jackrabbit.oak.segment

Class SegmentCache

java.lang.Object

org.apache.jackrabbit.oak.segment.SegmentCache

public abstract class SegmentCache
extends Object

A cache for data Segment instances by their SegmentId. This cache ignores bulk segments.

Conceptually this cache serves as a 2nd level cache for segments. The 1st level cache is implemented by memoising the segment in its id (see SegmentId#segment. Every time an segment is evicted from this cache the memoised segment is discarded (see SegmentId#onAccess.

Field Summary

Fields

Modifier and Type	Field	Description
static final int	DEFAULT_SEGMENT_CACHE_MB	Default maximum weight of this cache in MB

Constructor Summary

Constructors

Constructor	Description
SegmentCache()

Method Summary

Modifier and Type	Method	Description
abstract void	clear()	Clear all segment from the cache
abstract @NotNull AbstractCacheStats	getCacheStats()
abstract @NotNull Segment	getSegment(@NotNull SegmentId id, @NotNull Callable<Segment> loader)	Retrieve an segment from the cache or load it and cache it if not yet in the cache.
static @NotNull SegmentCache	newSegmentCache(long cacheSizeMB)	Create a new segment cache of the given size.
abstract void	putSegment(@NotNull Segment segment)	Put a segment into the cache.
abstract void	recordHit()	Record a hit in this cache's underlying statistics.

Methods inherited from class java.lang.Object

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

Field Details

DEFAULT_SEGMENT_CACHE_MB

public static final int DEFAULT_SEGMENT_CACHE_MB

Default maximum weight of this cache in MB

See Also:

• Constant Field Values

Constructor Details

SegmentCache

public SegmentCache()

Method Details

newSegmentCache

@NotNull
public static @NotNull SegmentCache newSegmentCache(long cacheSizeMB)

Create a new segment cache of the given size. Returns an always empty cache for cacheSizeMB <= 0.

Parameters:

cacheSizeMB - size of the cache in megabytes.

getSegment

@NotNull
public abstract @NotNull Segment getSegment(@NotNull
 @NotNull SegmentId id,
 @NotNull
 @NotNull Callable<Segment> loader)
                                     throws ExecutionException

Retrieve an segment from the cache or load it and cache it if not yet in the cache.

Parameters:

id - the id of the segment

loader - the loader to load the segment if not yet in the cache

Returns:

the segment identified by id

Throws:

ExecutionException - when loader failed to load an segment

putSegment

public abstract void putSegment(@NotNull
 @NotNull Segment segment)

Put a segment into the cache. This method does nothing for bulk segments.

Parameters:

segment - the segment to cache

clear

public abstract void clear()

Clear all segment from the cache

getCacheStats

@NotNull
public abstract @NotNull AbstractCacheStats getCacheStats()

Returns:

Statistics for this cache.

recordHit

public abstract void recordHit()

Record a hit in this cache's underlying statistics. See SegmentId#onAccess