SegmentDescriptor (Copycat API Reference (1.1.4))

java.lang.Object
- io.atomix.copycat.server.storage.SegmentDescriptor

All Implemented Interfaces:

AutoCloseable
```
public final class SegmentDescriptor
extends Object
implements AutoCloseable
```
Stores information about a Segment of the log.
The segment descriptor manages metadata related to a single segment of the log. Descriptors are stored within the first 48 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.
- range (64-bit signed integer) - The effective length of the segment. Regardless of the actual number of entries in the segment, the range indicates the total number of allowed entries within each segment. If a segment's index is 1 and its range is 10 then the next segment should start at index 11.
- 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.
- 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.
- maxEntrySize (32-bit signed integer) - The maximum length in bytes of entry values allowed by the segment.
- entries (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.
- 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.
Author:

Jordan Halterman

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class SegmentDescriptor.Builder
Segment descriptor builder.

Nested Classes
Modifier and Type	Class and Description
`static class`	`SegmentDescriptor.Builder` Segment descriptor builder.

Field Summary

Fields
Modifier and Type Field and Description

static int BYTES

Fields
Modifier and Type	Field and Description
`static int`	`BYTES`

Constructor Summary

Constructors
Constructor and Description

SegmentDescriptor(Buffer buffer)

Constructors
Constructor and Description
`SegmentDescriptor(Buffer buffer)`

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`static SegmentDescriptor.Builder`	`builder()` Returns a descriptor builder.
`static SegmentDescriptor.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.
`void`	`lock()` Locks the segment.
`boolean`	`locked()` Returns whether the segment has been locked by commitment.
`int`	`maxEntries()` Returns the maximum number of entries allowed in the segment.
`long`	`maxSegmentSize()` Returns the maximum count of the segment.
`void`	`update(long timestamp)` Writes an update to the descriptor.
`long`	`updated()` Returns last time the segment was updated.
`long`	`version()` Returns the segment version.

Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - BYTES
```
public static final int BYTES
```
    See Also:
    
    Constant Field Values
- Constructor Detail
  - SegmentDescriptor
```
public SegmentDescriptor(Buffer buffer)
```
    Throws:
    
    NullPointerException - if buffer is null
- Method Detail
  - builder
```
public static SegmentDescriptor.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 SegmentDescriptor.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
  - 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.
  - version
```
public long version()
```
    Returns the segment version.
    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.
    
    Returns:
    
    The segment version.
  - 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 long 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.
  - locked
```
public boolean locked()
```
    Returns whether the segment has been locked by commitment.
    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.
    
    Returns:
    
    Indicates whether the segment has been locked.
  - lock
```
public void lock()
```
    Locks the segment.
  - close
```
public void close()
```
    Specified by:
    
    close in interface AutoCloseable
  - delete
```
public void delete()
```
    Deletes the descriptor.

Class SegmentDescriptor

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

BYTES

Constructor Detail

SegmentDescriptor

Method Detail

builder

builder

id

version

index

maxSegmentSize

maxEntries

updated

update

locked

lock

close

delete