org.rocksdb

Class AbstractComparator<T extends org.rocksdb.AbstractSlice<?>>

java.lang.Object

org.rocksdb.RocksObject

org.rocksdb.AbstractComparator<T>

Direct Known Subclasses:

Comparator, DirectComparator

public abstract class AbstractComparator<T extends org.rocksdb.AbstractSlice<?>>
extends RocksObject

Comparators are used by RocksDB to determine the ordering of keys. This class is package private, implementers should extend either of the public abstract classes:

See Also:

Comparator, DirectComparator

Field Summary

Fields inherited from class org.rocksdb.RocksObject

nativeHandle_

Constructor Summary

Constructors

Constructor and Description
AbstractComparator()

Method Summary

Methods

Modifier and Type	Method and Description
abstract int	compare(T a, T b) Three-way key comparison
protected void	disposeInternal() Deletes underlying C++ comparator pointer.
java.lang.String	findShortestSeparator(java.lang.String start, T limit) Used to reduce the space requirements for internal data structures like index blocks.
java.lang.String	findShortSuccessor(java.lang.String key) Used to reduce the space requirements for internal data structures like index blocks.
abstract java.lang.String	name() The name of the comparator.

Methods inherited from class org.rocksdb.RocksObject

disOwnNativeHandle, dispose, finalize, isInitialized, isOwningNativeHandle

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

AbstractComparator

public AbstractComparator()

Method Detail

name

public abstract java.lang.String name()

The name of the comparator. Used to check for comparator mismatches (i.e., a DB created with one comparator is accessed using a different comparator). A new name should be used whenever the comparator implementation changes in a way that will cause the relative ordering of any two keys to change. Names starting with "rocksdb." are reserved and should not be used.

Returns:

The name of this comparator implementation

compare

public abstract int compare(T a,
          T b)

Three-way key comparison

Parameters:

a - Slice access to first key

b - Slice access to second key

Returns:

Should return either: 1) < 0 if "a" < "b" 2) == 0 if "a" == "b" 3) > 0 if "a" > "b"

findShortestSeparator

public java.lang.String findShortestSeparator(java.lang.String start,
                                     T limit)

Used to reduce the space requirements for internal data structures like index blocks.

If start < limit, you may return a new start which is a shorter string in [start, limit).

Simple comparator implementations may return null if they wish to use start unchanged. i.e., an implementation of this method that does nothing is correct.

Parameters:

start - String

limit - of type T

Returns:

a shorter start, or null

findShortSuccessor

public java.lang.String findShortSuccessor(java.lang.String key)

Used to reduce the space requirements for internal data structures like index blocks.

You may return a new short key (key1) where key1 ≥ key.

Simple comparator implementations may return null if they wish to leave the key unchanged. i.e., an implementation of this method that does nothing is correct.

Parameters:

key - String

Returns:

a shorter key, or null

disposeInternal

protected void disposeInternal()

Deletes underlying C++ comparator pointer. Note that this function should be called only after all RocksDB instances referencing the comparator are closed. Otherwise an undefined behavior will occur.

Specified by:

disposeInternal in class RocksObject