OffsetIndex (Copycat API Reference (1.2.8))

All Superinterfaces:

AutoCloseable

All Known Implementing Classes:

DelegatingOffsetIndex, SearchableOffsetIndex, SequentialOffsetIndex
```
public interface OffsetIndex
extends AutoCloseable
```
Segment offset index.
The offset index handles indexing of entries in a given Segment. Given the offset and position of an entry in a segment, the index will write the position to an underlying Buffer. With this information, the index provides useful metadata about the log such as the number of physical entries in the log and the first and last offsets.
Each entry in the index is stored in 8 bytes, a 1 byte status flag, a 24-bit unsigned offset, and a 32-bit unsigned position. This places a limitation on the maximum indexed offset at 2^31 - 1 and maximum indexed position at 2^32 - 1.
When the index is first created, the Buffer provided to the constructor will be scanned for existing entries.
The index assumes that entries will always be indexed in increasing order. However, this index also allows arbitrary entries to be missing from the log due to log compaction. Because of the potential for missing entries, binary search is used to locate positions rather than absolute positions. For efficiency, a MappedBuffer can be used to improve the performance of the binary search algorithm for persistent indexes.
In order to prevent searching the index for missing entries, all offsets are added to a memory efficient BitArray as they're written to the index. The bit array is sized according to the underlying index buffer. Prior to searching for an offset in the index, the BitArray is checked for existence of the offset in the index. Only if the offset exists in the index is a binary search required.

Author:

Jordan Halterman

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method and Description
`void`	`close()` Closes the index.
`boolean`	`contains(long offset)` Returns a boolean value indicating whether the index contains the given offset.
`void`	`delete()` Deletes the index.
`long`	`find(long offset)` Finds the real offset for the given relative offset.
`void`	`flush()` Flushes the index to the underlying storage.
`boolean`	`index(long offset, long position)` Indexes the given offset with the given position.
`boolean`	`isEmpty()` Returns a boolean value indicating whether the index is empty.
`long`	`lastOffset()` Returns the last offset in the index.
`long`	`position(long offset)` Finds the starting position of the given offset.
`int`	`size()` Returns the number of entries active in the index.
`static long`	`size(int maxEntries)` Returns the count of the index for the given number of entries.
`long`	`truncate(long offset)` Truncates the index up to the given offset.

- Method Detail
  - size
```
static long size(int maxEntries)
```
    Returns the count of the index for the given number of entries.
  - lastOffset
```
long lastOffset()
```
    Returns the last offset in the index.
  - index
```
boolean index(long offset,
              long position)
```
    Indexes the given offset with the given position.
    
    Parameters:
    
    offset - The offset to index.
    
    position - The position of the offset to index.
    
    Returns:
    
    Indicates whether the offset was successfully indexed.
    
    Throws:
    
    IllegalArgumentException - if the offset is less than or equal to the last offset in the index, or position is greater than MAX_POSITION
  - isEmpty
```
boolean isEmpty()
```
    Returns a boolean value indicating whether the index is empty.
    
    Returns:
    
    Indicates whether the index is empty.
  - size
```
int size()
```
    Returns the number of entries active in the index.
    
    Returns:
    
    The number of entries active in the index.
  - contains
```
boolean contains(long offset)
```
    Returns a boolean value indicating whether the index contains the given offset.
    
    Parameters:
    
    offset - The offset to check.
    
    Returns:
    
    Indicates whether the index contains the given offset.
  - position
```
long position(long offset)
```
    Finds the starting position of the given offset.
    
    Parameters:
    
    offset - The offset to look up.
    
    Returns:
    
    The starting position of the given offset.
  - find
```
long find(long offset)
```
    Finds the real offset for the given relative offset.
  - truncate
```
long truncate(long offset)
```
    Truncates the index up to the given offset.
    This method assumes that the given offset is contained within the index. If the offset is not indexed then the index will not be truncated.
    
    Parameters:
    
    offset - The offset after which to truncate the index.
    
    Returns:
    
    The position of the last entry in the index.
  - flush
```
void flush()
```
    Flushes the index to the underlying storage.
  - close
```
void close()
```
    Closes the index.
    
    Specified by:
    
    close in interface AutoCloseable
  - delete
```
void delete()
```
    Deletes the index.

Interface OffsetIndex

Method Summary

Method Detail

size

lastOffset

index

isEmpty

size

contains

position

find

truncate

flush

close

delete