System.OutOfMemoryException - when Entity Framework is querying a too big data of Varbinary type

问题

I'm trying to query a varbinary column that contain a file (1,2 Gb).

I'm using Entity Framework. See below:

Database to test

CREATE TABLE [dbo].[BIGDATA]
(
    [id] [bigint] IDENTITY(1,1) NOT NULL,
    [BIGDATA] [varbinary](max) NULL, 

    CONSTRAINT [PK_BIGDATA] PRIMARY KEY CLUSTERED ([id] ASC) 
) ON [PRIMARY]

Data to test (any file with 1 Gb)

INSERT INTO [dbo].[BIGDATA]([BIGDATA])
VALUES
   ((SELECT BulkColumn FROM OPENROWSET(BULK N'C:\BigTest.txt', SINGLE_BLOB) AS Document))

Controller to download file

public FileResult Download()
{
        try
        {
            var context = new Models.ELOGTESTEEntities();

            var idArquivo = Convert.ToInt32(1);

            // The problem is here, when trying send command to SQL Server to read register
            var arquivo = (from item in context.BIGDATA
                           where item.id.Equals(idArquivo)
                           select item).Single();
            var mimeType = ".txt";              

            byte[] bytes = System.Text.Encoding.GetEncoding("iso-8859-8").GetBytes("BigTest.txt");
            return File(arquivo.BIGDATA1, mimeType, System.Text.Encoding.UTF8.GetString(bytes));
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }

I can querying normally on SQL Server with Select * From BigData.

But, in Entity Framework (or command with ADO) I get this exception:

System.OutOfMemoryException

Does someone know how fix this problem?

回答1:

Wow that is a lot data. I really think you need to not use EF to get this data, but instead use the good 'ol SqlDataReader.

Given your .net 4.0 restriction, I found a custom implementation of streaming a read from a massive varbinary column. I can't take any credit for this other than reviewing the code and making sure there are not .net 4.5 shortcuts in it:

http://www.syntaxwarriors.com/2013/stream-varbinary-data-to-and-from-mssql-using-csharp/

Mods - let me know if something like this should be copy/pasted into the answer as the original URL may not be persistent.

Edit: Here is the code from the link in case the URL goes away:

Usage:

// reading and returning data to the client
VarbinaryStream filestream = new VarbinaryStream(
                                DbContext.Database.Connection.ConnectionString, 
                                "FileContents", 
                                "Content", 
                                "ID", 
                                (int)filepost.ID, 
                                true);

// Do what you want with the stream here.

The code:

public class VarbinaryStream : Stream
{
    private SqlConnection _Connection;

    private string  _TableName;
    private string  _BinaryColumn;
    private string  _KeyColumn;
    private int     _KeyValue;

    private long    _Offset;

    private SqlDataReader _SQLReader;
    private long _SQLReadPosition;

    private bool _AllowedToRead = false;

    public VarbinaryStream(
        string ConnectionString,
        string TableName,
        string BinaryColumn,
        string KeyColumn,
        int KeyValue,
        bool AllowRead = false)
    {
        // create own connection with the connection string.
        _Connection = new SqlConnection(ConnectionString);

        _TableName = TableName;
        _BinaryColumn = BinaryColumn;
        _KeyColumn = KeyColumn;
        _KeyValue = KeyValue;


        // only query the database for a result if we are going to be reading, otherwise skip.
        _AllowedToRead = AllowRead;
        if (_AllowedToRead == true)
        {
            try
            {
                if (_Connection.State != ConnectionState.Open)
                    _Connection.Open();

                SqlCommand cmd = new SqlCommand(
                                @"SELECT TOP 1 [" + _BinaryColumn + @"]
                                FROM [dbo].[" + _TableName + @"]
                                WHERE [" + _KeyColumn + "] = @id",
                            _Connection);

                cmd.Parameters.Add(new SqlParameter("@id", _KeyValue));

                _SQLReader = cmd.ExecuteReader(
                    CommandBehavior.SequentialAccess |
                    CommandBehavior.SingleResult |
                    CommandBehavior.SingleRow |
                    CommandBehavior.CloseConnection);

                _SQLReader.Read();
            }
            catch (Exception e)
            {
                // log errors here
            }
        }
    }

    // this method will be called as part of the Stream ímplementation when we try to write to our VarbinaryStream class.
    public override void Write(byte[] buffer, int index, int count)
    {
        try
        {
            if (_Connection.State != ConnectionState.Open)
                _Connection.Open();

            if (_Offset == 0)
            {
                // for the first write we just send the bytes to the Column
                SqlCommand cmd = new SqlCommand(
                                            @"UPDATE [dbo].[" + _TableName + @"]
                                                SET [" + _BinaryColumn + @"] = @firstchunk 
                                            WHERE [" + _KeyColumn + "] = @id",
                                        _Connection);

                cmd.Parameters.Add(new SqlParameter("@firstchunk", buffer));
                cmd.Parameters.Add(new SqlParameter("@id", _KeyValue));

                cmd.ExecuteNonQuery();

                _Offset = count;
            }
            else
            {
                // for all updates after the first one we use the TSQL command .WRITE() to append the data in the database
                SqlCommand cmd = new SqlCommand(
                                        @"UPDATE [dbo].[" + _TableName + @"]
                                            SET [" + _BinaryColumn + @"].WRITE(@chunk, NULL, @length)
                                        WHERE [" + _KeyColumn + "] = @id",
                                     _Connection);

                cmd.Parameters.Add(new SqlParameter("@chunk", buffer));
                cmd.Parameters.Add(new SqlParameter("@length", count));
                cmd.Parameters.Add(new SqlParameter("@id", _KeyValue));

                cmd.ExecuteNonQuery();

                _Offset += count;
            }
        }
        catch (Exception e)
        {
            // log errors here
        }
    }

    // this method will be called as part of the Stream ímplementation when we try to read from our VarbinaryStream class.
    public override int Read(byte[] buffer, int offset, int count)
    {
        try
        {
            long bytesRead = _SQLReader.GetBytes(0, _SQLReadPosition, buffer, offset, count);
            _SQLReadPosition += bytesRead;
            return (int)bytesRead;
        }
        catch (Exception e)
        {
            // log errors here
        }
        return -1;
    }
    public override bool CanRead
    {
        get { return _AllowedToRead; }
    }

    #region unimplemented methods
    public override bool CanSeek
    {
        get { return false; }
    }

    public override bool CanWrite
    {
        get { return true; }
    }

    public override void Flush()
    {
        throw new NotImplementedException();
    }

    public override long Length
    {
        get { throw new NotImplementedException(); }
    }

    public override long Position
    {
        get
        {
            throw new NotImplementedException();
        }
        set
        {
            throw new NotImplementedException();
        }
    }
    public override long Seek(long offset, SeekOrigin origin)
    {
        throw new NotImplementedException();
    }

    public override void SetLength(long value)
    {
        throw new NotImplementedException();
    }
    #endregion unimplemented methods
}

回答2:

Try to load the Data with EF "AsNoTracking()" option!

Sample: MyContext.MyTable.AsNoTracking().Where( x => x.....)

回答3:

It appears Entity Framework doesn't support streaming the data to a varbinary field.

You have a couple of options.

Drop to ADO.NET for the large transfers.
Switch your database to FileStream instead of varbinary

Edit: Assuming you're using .NET 4.5, you should use SqlDataReader.GetStream. This will allow streaming the file without having to load the whole thing into memory.

来源：https://stackoverflow.com/questions/24613201/system-outofmemoryexception-when-entity-framework-is-querying-a-too-big-data-o

标签

entity-framework

out-of-memory

varbinary

querying