io.atomix.storage.journal

Class JournalSegmentDescriptor

java.lang.Object

io.atomix.storage.journal.JournalSegmentDescriptor

All Implemented Interfaces:

AutoCloseable

public final class JournalSegmentDescriptor
extends Object
implements AutoCloseable

Stores information about a JournalSegment of the log.

The segment descriptor manages metadata related to a single segment of the log. Descriptors are stored within the first 64 bytes of each segment in the following order:

• id (64-bit signed integer) - A unique segment identifier. This is a monotonically increasing number within each log. Segments with in-sequence identifiers should contain in-sequence indexes.
• index (64-bit signed integer) - The effective first index of the segment. This indicates the index at which the first entry should be written to the segment. Indexes are monotonically increasing thereafter.
• version (64-bit signed integer) - The version of the segment. Versions are monotonically increasing starting at 1. Versions will only be incremented whenever the segment is rewritten to another memory/disk space, e.g. after log compaction.
• maxSegmentSize (32-bit unsigned integer) - The maximum number of bytes allowed in the segment.
• maxEntries (32-bit signed integer) - The total number of expected entries in the segment. This is the final number of entries allowed within the segment both before and after compaction. This entry count is used to determine the count of internal indexing and deduplication facilities.
• updated (64-bit signed integer) - The last update to the segment in terms of milliseconds since the epoch. When the segment is first constructed, the updated time is 0. Once all entries in the segment have been committed, the updated time should be set to the current time. Log compaction should not result in a change to updated.
• locked (8-bit boolean) - A boolean indicating whether the segment is locked. Segments will be locked once all entries have been committed to the segment. The lock state of each segment is used to determine log compaction and recovery behavior.

The remainder of the 64 segment header bytes are reserved for future metadata.

Author:

Jordan Halterman

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	JournalSegmentDescriptor.Builder Segment descriptor builder.

Field Summary

Fields

Modifier and Type	Field and Description
static int	BYTES

Constructor Summary

Constructors

Constructor and Description
JournalSegmentDescriptor(Buffer buffer)

Method Summary

Modifier and Type	Method and Description
static JournalSegmentDescriptor.Builder	builder() Returns a descriptor builder.
static JournalSegmentDescriptor.Builder	builder(Buffer buffer) Returns a descriptor builder for the given descriptor buffer.
void	close()
void	delete() Deletes the descriptor.
long	id() Returns the segment identifier.
long	index() Returns the segment index.
int	maxEntries() Returns the maximum number of entries allowed in the segment.
int	maxSegmentSize() Returns the maximum count of the segment.
String	toString()
void	update(long timestamp) Writes an update to the descriptor.
long	updated() Returns last time the segment was updated.
int	version() Returns the segment version.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

BYTES

public static final int BYTES

See Also:

Constant Field Values

Constructor Detail

JournalSegmentDescriptor

public JournalSegmentDescriptor(Buffer buffer)

Throws:

NullPointerException - if buffer is null

Method Detail

builder

public static JournalSegmentDescriptor.Builder builder()

Returns a descriptor builder.

The descriptor builder will write segment metadata to a 48 byte in-memory buffer.

Returns:

The descriptor builder.

builder

public static JournalSegmentDescriptor.Builder builder(Buffer buffer)

Returns a descriptor builder for the given descriptor buffer.

Parameters:

buffer - The descriptor buffer.

Returns:

The descriptor builder.

Throws:

NullPointerException - if buffer is null

version

public int version()

Returns the segment version.

Versions are monotonically increasing starting at 1.

Returns:

The segment version.

id

public long id()

Returns the segment identifier.

The segment ID is a monotonically increasing number within each log. Segments with in-sequence identifiers should contain in-sequence indexes.

Returns:

The segment identifier.

index

public long index()

Returns the segment index.

The index indicates the index at which the first entry should be written to the segment. Indexes are monotonically increasing thereafter.

Returns:

The segment index.

maxSegmentSize

public int maxSegmentSize()

Returns the maximum count of the segment.

Returns:

The maximum allowed count of the segment.

maxEntries

public int maxEntries()

Returns the maximum number of entries allowed in the segment.

Returns:

The maximum number of entries allowed in the segment.

updated

public long updated()

Returns last time the segment was updated.

When the segment is first constructed, the updated time is 0. Once all entries in the segment have been committed, the updated time should be set to the current time. Log compaction should not result in a change to updated.

Returns:

The last time the segment was updated in terms of milliseconds since the epoch.

update

public void update(long timestamp)

Writes an update to the descriptor.

close

public void close()

Specified by:

close in interface AutoCloseable

delete

public void delete()

Deletes the descriptor.

toString

public String toString()

Overrides:

toString in class Object