Package org.apache.jackrabbit.oak.segment

Class SegmentCache

  • public abstract class SegmentCache
extends java.lang.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 int DEFAULT_SEGMENT_CACHE_MB
      Default maximum weight of this cache in MB

    • Constructor Summary

      Constructors 
      Constructor Description
      SegmentCache()  

    • Method Summary

      All Methods Static Methods Instance Methods Abstract Methods Concrete Methods 
      Modifier and Type Method Description
      abstract void clear()
      Clear all segment from the cache
      abstract @NotNull org.apache.jackrabbit.oak.cache.AbstractCacheStats getCacheStats()  
      abstract @NotNull Segment getSegment​(@NotNull SegmentId id, @NotNull java.util.concurrent.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 Detail

      • 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 Detail

      • SegmentCache

        public SegmentCache()

    • Method Detail

      • 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 java.util.concurrent.Callable<Segment> loader)
                                     throws java.util.concurrent.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:
        java.util.concurrent.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 org.apache.jackrabbit.oak.cache.AbstractCacheStats getCacheStats()
        Returns:
        Statistics for this cache.

      • recordHit

        public abstract void recordHit()
        Record a hit in this cache's underlying statistics. See SegmentId#onAccess