org.apache.lucene.facet.taxonomy.TaxonomyWriter Maven / Gradle / Ivy
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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.lucene.facet.taxonomy;
import java.io.Closeable;
import java.io.IOException;
import java.util.Map;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.TwoPhaseCommit;
/**
* TaxonomyWriter is the interface which the faceted-search library uses
* to dynamically build the taxonomy at indexing time.
*
* Notes about concurrent access to the taxonomy:
*
* An implementation must allow multiple readers and a single writer to be
* active concurrently. Readers follow so-called "point in time" semantics,
* i.e., a reader object will only see taxonomy entries which were available
* at the time it was created. What the writer writes is only available to
* (new) readers after the writer's commit() is called.
*
* Faceted search keeps two indices - namely Lucene's main index, and this
* taxonomy index. When one or more readers are active concurrently with the
* writer, care must be taken to avoid an inconsistency between the state of
* these two indices: When writing to the indices, the taxonomy must always
* be committed to disk *before* the main index, because the main index
* refers to categories listed in the taxonomy.
* Such control can best be achieved by turning off the main index's
* "autocommit" feature, and explicitly calling commit() for both indices
* (first for the taxonomy, then for the main index).
* In old versions of Lucene (2.2 or earlier), when autocommit could not be
* turned off, a more complicated solution needs to be used. E.g., use
* some sort of (possibly inter-process) locking to ensure that a reader
* is being opened only right after both indices have been flushed (and
* before anything else is written to them).
*
* @lucene.experimental
*/
public interface TaxonomyWriter extends Closeable, TwoPhaseCommit {
/**
* addCategory() adds a category with a given path name to the taxonomy,
* and returns its ordinal. If the category was already present in
* the taxonomy, its existing ordinal is returned.
*
* Before adding a category, addCategory() makes sure that all its
* ancestor categories exist in the taxonomy as well. As result, the
* ordinal of a category is guaranteed to be smaller then the ordinal of
* any of its descendants.
*/
public int addCategory(FacetLabel categoryPath) throws IOException;
/**
* getParent() returns the ordinal of the parent category of the category
* with the given ordinal.
*
* When a category is specified as a path name, finding the path of its
* parent is as trivial as dropping the last component of the path.
* getParent() is functionally equivalent to calling getPath() on the
* given ordinal, dropping the last component of the path, and then calling
* getOrdinal() to get an ordinal back.
*
* If the given ordinal is the ROOT_ORDINAL, an INVALID_ORDINAL is returned.
* If the given ordinal is a top-level category, the ROOT_ORDINAL is returned.
* If an invalid ordinal is given (negative or beyond the last available
* ordinal), an ArrayIndexOutOfBoundsException is thrown. However, it is
* expected that getParent will only be called for ordinals which are
* already known to be in the taxonomy.
* TODO (Facet): instead of a getParent(ordinal) method, consider having a
*
* getCategory(categorypath, prefixlen) which is similar to addCategory
* except it doesn't add new categories; This method can be used to get
* the ordinals of all prefixes of the given category, and it can use
* exactly the same code and cache used by addCategory() so it means less code.
*/
public int getParent(int ordinal) throws IOException;
/**
* getSize() returns the number of categories in the taxonomy.
*
* Because categories are numbered consecutively starting with 0, it
* means the taxonomy contains ordinals 0 through getSize()-1.
*
* Note that the number returned by getSize() is often slightly higher
* than the number of categories inserted into the taxonomy; This is
* because when a category is added to the taxonomy, its ancestors
* are also added automatically (including the root, which always get
* ordinal 0).
*/
public int getSize();
/**
* Sets the commit user data iterable. See {@link IndexWriter#setLiveCommitData}.
*/
public void setLiveCommitData(Iterable> commitUserData);
/**
* Returns the commit user data iterable that was set on
* {@link #setLiveCommitData(Iterable)}.
*/
public Iterable> getLiveCommitData();
}