MergePolicy.cs

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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
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using System;
using System.Collections.Generic;
using Directory = Lucene.Net.Store.Directory;

namespace Lucene.Net.Index
{
    
    /// <summary> <p/>Expert: a MergePolicy determines the sequence of
    /// primitive merge operations to be used for overall merge
    /// and optimize operations.<p/>
    /// 
    /// <p/>Whenever the segments in an index have been altered by
    /// <see cref="IndexWriter" />, either the addition of a newly
    /// flushed segment, addition of many segments from
    /// addIndexes* calls, or a previous merge that may now need
    /// to cascade, <see cref="IndexWriter" /> invokes <see cref="FindMerges" />
    /// to give the MergePolicy a chance to pick
    /// merges that are now required.  This method returns a
    /// <see cref="MergeSpecification" /> instance describing the set of
    /// merges that should be done, or null if no merges are
    /// necessary.  When IndexWriter.optimize is called, it calls
    /// <see cref="FindMergesForOptimize" /> and the MergePolicy should
    /// then return the necessary merges.<p/>
    /// 
    /// <p/>Note that the policy can return more than one merge at
    /// a time.  In this case, if the writer is using <see cref="SerialMergeScheduler" />
    ///, the merges will be run
    /// sequentially but if it is using <see cref="ConcurrentMergeScheduler" />
    /// they will be run concurrently.<p/>
    /// 
    /// <p/>The default MergePolicy is <see cref="LogByteSizeMergePolicy" />
    ///.<p/>
    /// 
    /// <p/><b>NOTE:</b> This API is new and still experimental
    /// (subject to change suddenly in the next release)<p/>
    /// 
    /// <p/><b>NOTE</b>: This class typically requires access to
    /// package-private APIs (e.g. <c>SegmentInfos</c>) to do its job;
    /// if you implement your own MergePolicy, you'll need to put
    /// it in package Lucene.Net.Index in order to use
    /// these APIs.
    /// </summary>
    
    public abstract class MergePolicy : IDisposable
    {
        
        /// <summary>OneMerge provides the information necessary to perform
        /// an individual primitive merge operation, resulting in
        /// a single new segment.  The merge spec includes the
        /// subset of segments to be merged as well as whether the
        /// new segment should use the compound file format. 
        /// </summary>
        
        public class OneMerge
        {
            
            internal SegmentInfo info;              // used by IndexWriter
            internal bool mergeDocStores;           // used by IndexWriter
            internal bool optimize;                 // used by IndexWriter
            internal bool registerDone;             // used by IndexWriter
            internal long mergeGen;                 // used by IndexWriter
            internal bool isExternal;               // used by IndexWriter
            internal int maxNumSegmentsOptimize;    // used by IndexWriter
            internal SegmentReader[] readers;       // used by IndexWriter
            internal SegmentReader[] readersClone;  // used by IndexWriter
            internal SegmentInfos segments;
            internal bool useCompoundFile;
            internal bool aborted;
            internal System.Exception error;
            
            public OneMerge(SegmentInfos segments, bool useCompoundFile)
            {
                if (0 == segments.Count)
                    throw new ArgumentException("segments must include at least one segment", "segments");
                this.segments = segments;
                this.useCompoundFile = useCompoundFile;
            }
            
            /// <summary>Record that an exception occurred while executing
            /// this merge 
            /// </summary>
            internal virtual void  SetException(System.Exception error)
            {
                lock (this)
                {
                    this.error = error;
                }
            }
            
            /// <summary>Retrieve previous exception set by <see cref="SetException" />
            ///. 
            /// </summary>
            internal virtual System.Exception GetException()
            {
                lock (this)
                {
                    return error;
                }
            }
            
            /// <summary>Mark this merge as aborted.  If this is called
            /// before the merge is committed then the merge will
            /// not be committed. 
            /// </summary>
            internal virtual void  Abort()
            {
                lock (this)
                {
                    aborted = true;
                }
            }
            
            /// <summary>Returns true if this merge was aborted. </summary>
            internal virtual bool IsAborted()
            {
                lock (this)
                {
                    return aborted;
                }
            }
            
            internal virtual void  CheckAborted(Directory dir)
            {
                lock (this)
                {
                    if (aborted)
                        throw new MergeAbortedException("merge is aborted: " + SegString(dir));
                }
            }
            
            internal virtual String SegString(Directory dir)
            {
                var b = new System.Text.StringBuilder();
                int numSegments = segments.Count;
                for (int i = 0; i < numSegments; i++)
                {
                    if (i > 0)
                        b.Append(' ');
                    b.Append(segments.Info(i).SegString(dir));
                }
                if (info != null)
                    b.Append(" into ").Append(info.name);
                if (optimize)
                    b.Append(" [optimize]");
                if (mergeDocStores)
                {
                    b.Append(" [mergeDocStores]");
                }
                return b.ToString();
            }

            public SegmentInfos segments_ForNUnit
            {
                get { return segments; }
            }
        }
        
        /// <summary> A MergeSpecification instance provides the information
        /// necessary to perform multiple merges.  It simply
        /// contains a list of <see cref="OneMerge" /> instances.
        /// </summary>
        
        public class MergeSpecification
        {
            
            /// <summary> The subset of segments to be included in the primitive merge.</summary>
            
            public IList<OneMerge> merges = new List<OneMerge>();
            
            public virtual void  Add(OneMerge merge)
            {
                merges.Add(merge);
            }
            
            public virtual String SegString(Directory dir)
            {
                var b = new System.Text.StringBuilder();
                b.Append("MergeSpec:\n");
                int count = merges.Count;
                for (int i = 0; i < count; i++)
                    b.Append("  ").Append(1 + i).Append(": ").Append(merges[i].SegString(dir));
                return b.ToString();
            }
        }
        
        /// <summary>Exception thrown if there are any problems while
        /// executing a merge. 
        /// </summary>
        [Serializable]
        public class MergeException:System.SystemException
        {
            private readonly Directory dir;

            public MergeException(System.String message, Directory dir):base(message)
            {
                this.dir = dir;
            }

            public MergeException(System.Exception exc, Directory dir):base(null, exc)
            {
                this.dir = dir;
            }

            /// <summary>Returns the <see cref="Directory" /> of the index that hit
            /// the exception. 
            /// </summary>
            public virtual Directory Directory
            {
                get { return dir; }
            }
        }
        
        [Serializable]
        public class MergeAbortedException:System.IO.IOException
        {
            public MergeAbortedException():base("merge is aborted")
            {
            }
            public MergeAbortedException(System.String message):base(message)
            {
            }
        }
        
        protected internal IndexWriter writer;

        protected MergePolicy(IndexWriter writer)
        {
            this.writer = writer;
        }
        
        /// <summary> Determine what set of merge operations are now necessary on the index.
        /// <see cref="IndexWriter" /> calls this whenever there is a change to the segments.
        /// This call is always synchronized on the <see cref="IndexWriter" /> instance so
        /// only one thread at a time will call this method.
        /// 
        /// </summary>
        /// <param name="segmentInfos">the total set of segments in the index
        /// </param>
        public abstract MergeSpecification FindMerges(SegmentInfos segmentInfos);

        /// <summary> Determine what set of merge operations is necessary in order to optimize
        /// the index. <see cref="IndexWriter" /> calls this when its
        /// <see cref="IndexWriter.Optimize()" /> method is called. This call is always
        /// synchronized on the <see cref="IndexWriter" /> instance so only one thread at a
        /// time will call this method.
        /// 
        /// </summary>
        /// <param name="segmentInfos">the total set of segments in the index
        /// </param>
        /// <param name="maxSegmentCount">requested maximum number of segments in the index (currently this
        /// is always 1)
        /// </param>
        /// <param name="segmentsToOptimize">contains the specific SegmentInfo instances that must be merged
        /// away. This may be a subset of all SegmentInfos.
        /// </param>
        public abstract MergeSpecification FindMergesForOptimize(SegmentInfos segmentInfos, int maxSegmentCount,
                                                                 ISet<SegmentInfo> segmentsToOptimize);
        
        /// <summary> Determine what set of merge operations is necessary in order to expunge all
        /// deletes from the index.
        /// 
        /// </summary>
        /// <param name="segmentInfos">the total set of segments in the index
        /// </param>
        public abstract MergeSpecification FindMergesToExpungeDeletes(SegmentInfos segmentInfos);

        /// <summary> Release all resources for the policy.</summary>
        [Obsolete("Use Dispose() instead")]
        public void Close()
        {
            Dispose();
        }

        /// <summary> Release all resources for the policy.</summary>
        public void Dispose()
        {
            Dispose(true);
        }

        protected abstract void Dispose(bool disposing);
        
        /// <summary> Returns true if a newly flushed (not from merge)
        /// segment should use the compound file format.
        /// </summary>
        public abstract bool UseCompoundFile(SegmentInfos segments, SegmentInfo newSegment);
        
        /// <summary> Returns true if the doc store files should use the
        /// compound file format.
        /// </summary>
        public abstract bool UseCompoundDocStore(SegmentInfos segments);
    }
}