Interesting Lucene.net Exception

Question

According to this or this, I used the same indexsearcher by multiple thread. But when I switched from FsDirectory to MMapDirectory, I got interesting exceptions.

This work fine:

static void Main(string[] args) 
{
    DirectoryInfo directoryInfo = new DirectoryInfo(@"C:\Users\Tams\Desktop\new\");
    var directory = FSDirectory.Open(directoryInfo);
    var indexSearcher = new IndexSearcher(directory);

    const int times = 100;
    const int concurrentTaskCount = 5;
    var task = new Task[concurrentTaskCount];
    for (int i = 0; i < concurrentTaskCount; i++) 
    {
        task[i] = new Task(() => Search(indexSearcher, times));
        task[i].Start();
    }

    Task.WaitAll(task);
}

static void Search(IndexSearcher reader, int times) 
{
    List<Document> docs = new List<Document>(10000);
    for (int i = 0; i < times; i++) 
    {
        var q = new TermQuery(new Term("title", "volume"));
        foreach (var scoreDoc in reader.Search(q, 100).ScoreDocs)
        {
            docs.Add(reader.Doc(scoreDoc.Doc));
        }
    }
}

But with this:

static void Main(string[] args)
 {
    DirectoryInfo directoryInfo = new DirectoryInfo(@"C:\Users\Tams\Desktop\new\");
    var directory = new MMapDirectory(directoryInfo); // CHANGED
    var indexSearcher = new IndexSearcher(directory);

    const int times = 100;
    const int concurrentTaskCount = 5;
    var task = new Task[concurrentTaskCount];
    for (int i = 0; i < concurrentTaskCount; i++)
    {
        task[i] = new Task(() => Search(indexSearcher, times));
        task[i].Start();
    }

    Task.WaitAll(task);
}

static void Search(IndexSearcher reader, int times)
 {
    List<Document> docs = new List<Document>(10000);
    for (int i = 0; i < times; i++) 
   {
        var q = new TermQuery(new Term("title", "volume"));
        foreach (var scoreDoc in reader.Search(q, 100).ScoreDocs)
        {
            docs.Add(reader.Doc(scoreDoc.Doc));
        }
    }
}

I get various exceptions like:

System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative 
                                    and less than the size of the collection.
Parameter name: index
at System.ThrowHelper.ThrowArgumentOutOfRangeException()
at System.Collections.Generic.List`1.get_Item(Int32 index)
at Lucene.Net.Index.FieldInfos.FieldInfo(Int32 fieldNumber)
    in d:\Lucene.Net\FullRepo\trunk\src\core\Index\FieldInfos.cs:line 378   
at Lucene.Net.Index.FieldsReader.Doc(Int32 n, FieldSelector fieldSelector) 
    in d:\Lucene.Net\FullRepo\trunk\src\core\Index\FieldsReader.cs:line 234  
at Lucene.Net.Index.SegmentReader.Document(Int32 n, FieldSelector fieldSelector)
    in d:\Lucene.Net\FullRepo\trunk\src\core\Index\SegmentReader.cs:line 1193
at Lucene.Net.Index.DirectoryReader.Document(Int32 n, FieldSelector fieldSelector)
    in d:\Lucene.Net\FullRepo\trunk\src\core\Index\DirectoryReader.cs:line 686
at Lucene.Net.Index.IndexReader.Document(Int32 n) 
    in d:\Lucene.Net\FullRepo\trunk\src\core\Index\IndexReader.cs:line 732
at Lucene.Net.Search.IndexSearcher.Doc(Int32 i)
    in d:\Lucene.Net\FullRepo\trunk\src\core\Search\IndexSearcher.cs:line 162
at PerformanceTest.Program.Search(IndexSearcher reader, Int32 times)
    in c:\Users\Tams\Documents\Visual Studio 2012\Projects\BookCatalog\PerformanceTest\Program.cs:line 28
at PerformanceTest.Program.<>c__DisplayClass2.<Main>b__0()
    in c:\Users\Tams\Documents\Visual Studio 2012\Projects\BookCatalog\PerformanceTest\Program.cs:line 43
at System.Threading.Tasks.Task.InnerInvoke()
at System.Threading.Tasks.Task.Execute()

Or

System.IO.IOException: read past EOF
at Lucene.Net.Store.BufferedIndexInput.Refill()
    in d:\Lucene.Net\FullRepo\trunk\src\core\Store\BufferedIndexInput.cs:line 179
at Lucene.Net.Store.BufferedIndexInput.ReadByte()
    in d:\Lucene.Net\FullRepo\trunk\src\core\Store\BufferedIndexInput.cs:line 41
at Lucene.Net.Store.IndexInput.ReadVInt()
    in d:\Lucene.Net\FullRepo\trunk\src\core\Store\IndexInput.cs:line 88   
at Lucene.Net.Index.FieldsReader.Doc(Int32 n, FieldSelector fieldSelector)
    in d:\Lucene.Net\FullRepo\trunk\src\core\Index\FieldsReader.cs:line 230  
at Lucene.Net.Index.SegmentReader.Document(Int32 n, FieldSelector fieldSelector)
    in d:\Lucene.Net\FullRepo\trunk\src\core\Index\SegmentReader.cs:line 1193
at Lucene.Net.Index.DirectoryReader.Document(Int32 n, FieldSelector fieldSelector)
    in d:\Lucene.Net\FullRepo\trunk\src\core\Index\DirectoryReader.cs:line 686
at Lucene.Net.Index.IndexReader.Document(Int32 n)
    in d:\Lucene.Net\FullRepo\trunk\src\core\Index\IndexReader.cs:line 732   
at Lucene.Net.Search.IndexSearcher.Doc(Int32 i)
    in d:\Lucene.Net\FullRepo\trunk\src\core\Search\IndexSearcher.cs:line 162
at PerformanceTest.Program.Search(IndexSearcher reader, Int32 times)
    in c:\Users\Tams\Documents\Visual Studio 2012\Projects\BookCatalog\PerformanceTest\Program.cs:line 28
at PerformanceTest.Program.<>c__DisplayClass2.<Main>b__0()
    in c:\Users\Tams\Documents\Visual Studio 2012\Projects\BookCatalog\PerformanceTest\Program.cs:line 43
at System.Threading.Tasks.Task.InnerInvoke()
at System.Threading.Tasks.Task.Execute()

The last code work fine, with setting the concurrentTaskCount variable to 1.

Am I missing something? I cant figure out what that is.

Actually, I dont have the path

d:\Lucene.Net\FullRepo\trunk\src\core\Store\BufferedIndexInput.cs

I don't even have a drive with letter "d"

Answer 1

The source for MMapDirectory shows that this class does not use memory-mapped files, as expected. It loads all index files into memory using MemoryStream objects, and I would guess that those streams are the cause of the problem when different threads seeks and reads.

You can get a memory-based index by loading it into a RAMDirectory. This passes your test. (But it does what MMapDirectory currently does, not necessarily what you expect it to do...)

var fsDirectory = FSDirectory.Open(directoryInfo);
var directory = new RAMDirectory(fsDirectory);