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IndexWriter.java
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IndexWriter.java
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/*
* Copyright (c) 2002-2016 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.index;
import java.io.Closeable;
import java.io.IOException;
/**
* Able to {@link #merge(Object, Object, ValueMerger)} and {@link #remove(Object)} key/value pairs
* into an {@link Index}. After all modifications have taken place the writer must be {@link #close() closed},
* typically using try-with-resource clause.
*
* @param <KEY> type of keys
* @param <VALUE> type of values
*/
public interface IndexWriter<KEY,VALUE> extends Closeable
{
/**
* Associate given {@code key} with given {@code value}.
* Any existing {@code value} associated with {@code key} will be overwritten.
*
* @param key key to associate with value
* @param value value to associate with key
* @throws IOException on index access error.
*/
void put( KEY key, VALUE value ) throws IOException;
/**
* If the {@code key} doesn't already exist in the index the {@code key} will be added and the {@code value}
* associated with it. If the {@code key} already exists then its existing {@code value} will be merged with
* the given {@code value}, using the {@link ValueMerger}. If the {@link ValueMerger} returns a non-null
* value that value will be associated with the {@code key}, otherwise (if it returns {@code null}) nothing will
* be written.
*
* @param key key for which to merge values.
* @param value value to merge with currently associated value for the {@code key}.
* @param valueMerger {@link ValueMerger} to consult if key already exists.
* @throws IOException on index access error.
*/
void merge( KEY key, VALUE value, ValueMerger<VALUE> valueMerger ) throws IOException;
/**
* Removes a key, returning it's associated value, if found.
*
* @param key key to remove.
* @return value which was associated with the remove key, if found, otherwise {@code null}.
* @throws IOException on index access error.
*/
VALUE remove( KEY key ) throws IOException;
/**
* Options which applies to modifications, these options can aid implementations to do more things
* more efficiently in various scenarios.
*/
interface Options
{
/**
* Decides relatively where a split happens, i.e. which position will be the split key.
* Keys (and its values/children) including the split key will go to the right tree node,
* everything before it goes into the left.
*
* @return a factor between 0..1 where 0 means far to the left, 1 means far to the right and
* as an example 0.5 will select the middle item (floor division).
*/
float splitLeftChildSize();
class Defaults implements Options
{
@Override
public float splitLeftChildSize()
{
return 0.5f;
}
}
/**
* Default options best suitable for most occasions.
*/
Options DEFAULTS = new Defaults();
/**
* Options best suitable in batching scenarios, where insertions come in sequentially (by order of key)
* and are typically densely packed.
*/
Options BATCHING_SEQUENTIAL = new Defaults()
{
@Override
public float splitLeftChildSize()
{
return 1f;
}
};
}
}