org.rocksdb

Class AbstractComparator

java.lang.Object

org.rocksdb.AbstractNativeReference

org.rocksdb.AbstractImmutableNativeReference

org.rocksdb.RocksCallbackObject

org.rocksdb.AbstractComparator

All Implemented Interfaces:

AutoCloseable

Direct Known Subclasses:

BytewiseComparator, IntComparator, NativeComparatorWrapper, ReverseBytewiseComparator

public abstract class AbstractComparator
extends RocksCallbackObject

Comparators are used by RocksDB to determine the ordering of keys. Implementations of Comparators in Java should extend this class.

Field Summary

Fields inherited from class org.rocksdb.RocksCallbackObject

nativeHandle_

Fields inherited from class org.rocksdb.AbstractImmutableNativeReference

owningHandle_

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AbstractComparator(ComparatorOptions copt)

Method Summary

Modifier and Type	Method and Description
abstract int	compare(ByteBuffer a, ByteBuffer b) Three-way key comparison.
void	findShortestSeparator(ByteBuffer start, ByteBuffer limit) Used to reduce the space requirements for internal data structures like index blocks.
void	findShortSuccessor(ByteBuffer key) Used to reduce the space requirements for internal data structures like index blocks.
protected long	initializeNative(long... nativeParameterHandles) Construct the Native C++ object which will callback to our object methods
abstract String	name() The name of the comparator.
boolean	usingDirectBuffers()

Methods inherited from class org.rocksdb.RocksCallbackObject

disposeInternal

Methods inherited from class org.rocksdb.AbstractImmutableNativeReference

close, disOwnNativeHandle, isOwningHandle

Methods inherited from class java.lang.Object

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

Constructor Detail

AbstractComparator

protected AbstractComparator(ComparatorOptions copt)

Method Detail

initializeNative

protected long initializeNative(long... nativeParameterHandles)

Description copied from class: RocksCallbackObject

Construct the Native C++ object which will callback to our object methods

Specified by:

initializeNative in class RocksCallbackObject

Parameters:

nativeParameterHandles - An array of native handles for any parameter objects that are needed during construction

Returns:

The native handle of the C++ object which will callback to us

name

public abstract 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(ByteBuffer a,
                            ByteBuffer b)

Three-way key comparison. Implementations should provide a total order on keys that might be passed to it. The implementation may modify the ByteBuffers passed in, though it would be unconventional to modify the "limit" or any of the underlying bytes. As a callback, RocksJava will ensure that a is a different instance from b.

Parameters:

a - buffer containing the first key in its "remaining" elements

b - buffer containing the second key in its "remaining" elements

Returns:

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

findShortestSeparator

public void findShortestSeparator(ByteBuffer start,
                                  ByteBuffer limit)

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

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

If you modify start, it is expected that you set the byte buffer so that a subsequent read of start.remaining() bytes from start.position() to start.limit() will obtain the new start value.

Simple comparator implementations may return with start unchanged. i.e., an implementation of this method that does nothing is correct.

Parameters:

start - the start

limit - the limit

findShortSuccessor

public void findShortSuccessor(ByteBuffer key)

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

You may change key to a shorter key (key1) where key1 ≥ key.

Simple comparator implementations may return the key unchanged. i.e., an implementation of this method that does nothing is correct.

Parameters:

key - the key

usingDirectBuffers

public final boolean usingDirectBuffers()