Package org.apache.jackrabbit.oak.segment.file.tar

Class GCGeneration

java.lang.Object
org.apache.jackrabbit.oak.segment.file.tar.GCGeneration
public final class GCGeneration extends Object
Instances of this class represent the garbage collection generation related information of a segment. It consists of the segment's generation, its full generation and its compaction flag. The segment's generation records the number of garbage collection cycles a segment went through and is incremented with every garbage collection regardless its type. The segment's full generation records the number of full garbage collection cycles a segment went through. It is only incremented on full garbage collection cycles. The segment's compaction flag is set for those segments that have been created by a compaction operation. It is never set for segments created by normal write operations or defer compactions triggered by such. Segments written by normal repository writes will inherit the generation and full generation of the segment written by the previous compaction process with the compacted flag cleared.

The information recorded in this way allows to determine the reclamation status of a segment by just looking at the GCGeneration instances of that segment and of the segment containing the repository head: Let s be a segment, h be the segment containing the current repository head and n be the number of retained generations.

  • s is old iff h.generation - s.generation >= n
  • s is in the same compaction tail than h iff s.isCompacted && s.fullGeneration == h.fullGeneration
  • s is reclaimable iff s is old and s is not in the same compaction tail than h

  • Field Details

  • Method Details

    • newGCGeneration

      public static GCGeneration newGCGeneration(int generation, int fullGeneration, boolean isCompacted)

    • newGCGeneration

      public static GCGeneration newGCGeneration(SegmentArchiveEntry indexEntry)

    • getGeneration

      public int getGeneration()

    • getFullGeneration

      public int getFullGeneration()

    • isCompacted

      public boolean isCompacted()

    • nextFull

      @NotNull public @NotNull GCGeneration nextFull()
      Create a new instance with the generation and the full generation incremented by one and the compaction flag set.

    • nextTail

      @NotNull public @NotNull GCGeneration nextTail()
      Create a new instance with the generation incremented by one, the full generation left unchanged and the compaction flag set.

    • nextPartial

      @NotNull public @NotNull GCGeneration nextPartial()
      Create a new instance with the compaction flag set and the generation and the full generation left unchanged.

    • nonGC

      @NotNull public @NotNull GCGeneration nonGC()
      Create a new instance with the compaction flag unset and the generation and the full generation left unchanged.

    • compareWith

      public int compareWith(@NotNull @NotNull GCGeneration gcGeneration)
      Compare this generation with gcGeneration
      Parameters:
      gcGeneration - the generation this generation is compared against.
      Returns:
      Number of generations between this generation and gcGeneration

    • compareFullGenerationWith

      public int compareFullGenerationWith(@NotNull @NotNull GCGeneration gcGeneration)
      Compare this full generation the full generation of gcGeneration
      Parameters:
      gcGeneration - the generation this generation is compared against.
      Returns:
      Number of generations between the full generations of this generation and gcGeneration

    • equals

      public boolean equals(Object other)
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object

    • toString

      public String toString()
      Overrides:
      toString in class Object