c# - Failed to write large amount of data to stream

Question

When I'm trying to write very large amount of data (list with 300 000 rows and more) to memory stream using CsvHelper, it throws the exception "System.IO.IOException: Stream was too long.".

Data class is rather big and has ~30 properties, consequently each record in the file would have ~30 columns.

This is the actual writing code where exception throws (by the way this code is based on that answer of CsvHelper lib's author):

using (var memoryStream = new MemoryStream())
{
    using (var streamWriter = new StreamWriter(memoryStream, encoding ?? Encoding.ASCII))
    {
        var csvWriter = new CsvWriter(streamWriter, GetConfiguration(delimiter, mappingClassType, mappingActions));
        csvWriter.WriteRecords(data); //data is IEnumerable<T> and has more than 300k records

        streamWriter.Flush();
        return memoryStream.ToArray();
    }
}

Then I save the resulted bytes array into the file.

File.WriteAllBytes(filePath, resultedBytesArray); 

Please note, that the same code works well when I write 100 000 records to the file (in that case the file has size about 1GB). By the way, my goal is to write more then 600 000 data records.

This is the relevant part of the stack trace related to this issue.

Stream was too long.|System.IO.IOException: Stream was too long.
at System.IO.MemoryStream.Write(Byte[] buffer, Int32 offset, Int32 count) 
at System.IO.StreamWriter.Flush(Boolean flushStream, Boolean flushEncoder) 
at System.IO.StreamWriter.Write(Char[] buffer, Int32 index, Int32 count) 
at CsvHelper.CsvWriter.NextRecord() in C:UsersJoshProjectsCsvHelpersrcCsvHelperCsvWriter.cs:line 290 
at CsvHelper.CsvWriter.WriteRecords(IEnumerable records) in C:UsersJoshProjectsCsvHelpersrcCsvHelperCsvWriter.cs:line 490 
at FileExport.Csv.CsvDocument.Create[T](IEnumerable`1 data, String delimiter, Encoding encoding, Type mappingClassType, IDictionary`2 mappingActions) in d:DevDrugDevExportFileExportCsvCsvDocument.cs:line 33 

As far as I'm concerned the basic way to achieve my goal and avoid that issue is to split my list of written data up on few parts and concatenate them together then, but may be is there any pretty obvious and easy solution without a significant code refactoring (like increase the default stream/buffer size, etc..)?

Also keep in mind, that I've also applied two possible solutions in order to prevent "Out Of Memory" objects exception.

• got rid of 2GB limitation for objects (from here https://stackoverflow.com/a/20912869) Yes, I'm running on x64 OS with 32GB RAM.
• set up x64 "Platform target" in the build settings section (from here https://stackoverflow.com/a/22592876)

Thanks in advance.

Answer 1

You can address this limitation of 2GB by writing your own MemoryStream :

    class HugeMemoryStream : Stream
    {
        #region Fields

        private const int PAGE_SIZE = 1024000;
        private const int ALLOC_STEP = 1024;

        private byte[][] _streamBuffers;

        private int _pageCount = 0;
        private long _allocatedBytes = 0;

        private long _position = 0;
        private long _length = 0;

        #endregion Fields

        #region Internals

        private int GetPageCount(long length)
        {
            int pageCount = (int)(length / PAGE_SIZE) + 1;

            if ((length % PAGE_SIZE) == 0)
                pageCount--;

            return pageCount;
        }

        private void ExtendPages()
        {
            if (_streamBuffers == null)
            {
                _streamBuffers = new byte[ALLOC_STEP][];
            }
            else
            {
                byte[][] streamBuffers = new byte[_streamBuffers.Length + ALLOC_STEP][];

                Array.Copy(_streamBuffers, streamBuffers, _streamBuffers.Length);

                _streamBuffers = streamBuffers;
            }

            _pageCount = _streamBuffers.Length;
        }

        private void AllocSpaceIfNeeded(long value)
        {
            if (value < 0)
                throw new InvalidOperationException("AllocSpaceIfNeeded < 0");

            if (value == 0)
                return;

            int currentPageCount = GetPageCount(_allocatedBytes);
            int neededPageCount = GetPageCount(value);

            while (currentPageCount < neededPageCount)
            {
                if (currentPageCount == _pageCount)
                    ExtendPages();

                _streamBuffers[currentPageCount++] = new byte[PAGE_SIZE];
            }

            _allocatedBytes = (long)currentPageCount * PAGE_SIZE;

            value = Math.Max(value, _length);

            if (_position > (_length = value))
                _position = _length;
        }

        #endregion Internals

        #region Stream

        public override bool CanRead => true;

        public override bool CanSeek => true;

        public override bool CanWrite => true;

        public override long Length => _length;

        public override long Position
        {
            get { return _position; }
            set
            {
                if (value > _length)
                    throw new InvalidOperationException("Position > Length");
                else if (value < 0)
                    throw new InvalidOperationException("Position < 0");
                else
                    _position = value;
            }
        }

        public override void Flush() { }

        public override int Read(byte[] buffer, int offset, int count)
        {
            int currentPage = (int)(_position / PAGE_SIZE);
            int currentOffset = (int)(_position % PAGE_SIZE);
            int currentLength = PAGE_SIZE - currentOffset;

            long startPosition = _position;

            if (startPosition + count > _length)
                count = (int)(_length - startPosition);

            while (count != 0 && _position < _length)
            {
                if (currentLength > count)
                    currentLength = count;

                Array.Copy(_streamBuffers[currentPage++], currentOffset, buffer, offset, currentLength);

                offset += currentLength;
                _position += currentLength;
                count -= currentLength;

                currentOffset = 0;
                currentLength = PAGE_SIZE;
            }

            return (int)(_position - startPosition);
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            switch (origin)
            {
                case SeekOrigin.Begin:
                    break;

                case SeekOrigin.Current:
                    offset += _position;
                    break;

                case SeekOrigin.End:
                    offset = _length - offset;
                    break;

                default:
                    throw new ArgumentOutOfRangeException("origin");
            }

            return Position = offset;
        }

        public override void SetLength(long value)
        {
            if (value < 0)
                throw new InvalidOperationException("SetLength < 0");

            if (value == 0)
            {
                _streamBuffers = null;
                _allocatedBytes = _position = _length = 0;
                _pageCount = 0;
                return;
            }

            int currentPageCount = GetPageCount(_allocatedBytes);
            int neededPageCount = GetPageCount(value);

            // Removes unused buffers if decreasing stream length
            while (currentPageCount > neededPageCount)
                _streamBuffers[--currentPageCount] = null;

            AllocSpaceIfNeeded(value);

            if (_position > (_length = value))
                _position = _length;
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            int currentPage = (int)(_position / PAGE_SIZE);
            int currentOffset = (int)(_position % PAGE_SIZE);
            int currentLength = PAGE_SIZE - currentOffset;

            long startPosition = _position;

            AllocSpaceIfNeeded(_position + count);

            while (count != 0)
            {
                if (currentLength > count)
                    currentLength = count;

                Array.Copy(buffer, offset, _streamBuffers[currentPage++], currentOffset, currentLength);

                offset += currentLength;
                _position += currentLength;
                count -= currentLength;

                currentOffset = 0;
                currentLength = PAGE_SIZE;
            }
        }

        #endregion Stream
    }
using ICSharpCode.SharpZipLib.GZip;
using System;
using System.IO;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

            // HugeMemoryStrem Test

            string filename = @"gzip-filename.gz";

            HugeMemoryStream ms = new HugeMemoryStream();

            using (StreamWriter sw = new StreamWriter(ms, Encoding.UTF8, 16384, true))
            using (FileStream fs = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read))
            using (GZipInputStream gzipStream = new GZipInputStream(fs))
            using (StreamReader sr = new StreamReader(gzipStream, Encoding.UTF8, false, 16384, true))
            {
                for (string line = sr.ReadLine(); line != null; line = sr.ReadLine())
                    sw.WriteLine(line);
            }

            ms.Seek(0, SeekOrigin.Begin);

            using (StreamReader srm = new StreamReader(ms, Encoding.UTF8, false, 16384, true))
            using (FileStream fs = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read))
            using (GZipInputStream gzipStream = new GZipInputStream(fs))
            using (StreamReader sr = new StreamReader(gzipStream, Encoding.UTF8, false, 16384, true))
            {
                for (string line1 = sr.ReadLine(), line2 = srm.ReadLine(); line1 != null; line1 = sr.ReadLine(), line2 = srm.ReadLine())
                {
                    if (line1 != line2)
                        throw new InvalidDataException();
                }
            }