Package 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.

  • Constructor Details

    • AbstractComparator

      protected AbstractComparator(ComparatorOptions comparatorOptions)

  • Method Details

    • 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()