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 Summary

Fields

Modifier and Type	Field	Description
static GCGeneration	NULL

Method Summary

Modifier and Type	Method	Description
int	compareFullGenerationWith(@NotNull GCGeneration gcGeneration)	Compare this full generation the full generation of gcGeneration
int	compareWith(@NotNull GCGeneration gcGeneration)	Compare this generation with gcGeneration
boolean	equals(Object other)
int	getFullGeneration()
int	getGeneration()
int	hashCode()
boolean	isCompacted()
static GCGeneration	newGCGeneration(int generation, int fullGeneration, boolean isCompacted)
static GCGeneration	newGCGeneration(SegmentArchiveEntry indexEntry)
@NotNull GCGeneration	nextFull()	Create a new instance with the generation and the full generation incremented by one and the compaction flag left unchanged.
@NotNull GCGeneration	nextTail()	Create a new instance with the generation incremented by one and the full generation and the compaction flag left unchanged.
@NotNull GCGeneration	nonGC()	Create a new instance with the compaction flag unset and the generation and the full generation left unchanged.
String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

NULL

public static final GCGeneration NULL

Method Detail

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 left unchanged.

nextTail

@NotNull
public @NotNull GCGeneration nextTail()

Create a new instance with the generation incremented by one and the full generation and the compaction flag 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