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    <p>Your biggest bottleneck is going to be IO, which has to be performed with exclusive access to the file. The actual byte-crunching for this will be fast - you are going to do just as well writing it directly to the file (noting that the <code>FileStream</code> itself has a buffer, or you can add an extra layer with <code>BufferedStream</code>) than you would by serializing different parts in-memory and then copying each in-memory part to the stream separately.</p> <p>My advice: just write the data in a single thread. Frankly I'm not sure I'd even bother with <code>async</code> (hint: async code <strong>adds overhead</strong>), especially if the buffer is keeping up. I also wouldn't use <code>BiaryWriter</code> / <code>BinaryReader</code> - I'd just write it raw. One tricky you could do is to use some <code>unsafe</code> code to copy the data in blocks, to avoid having to even look at individual objects, but that is at the harder end of things... I'll try to do an example.</p> <p>Here's an example of read/write, noting performance first:</p> <pre><code>Write: 2012ms Read: 1089ms File: 838,860,804 bytes </code></pre> <p>Code:</p> <pre><code>[DllImport("msvcrt.dll", EntryPoint = "memcpy", CallingConvention = CallingConvention.Cdecl, SetLastError = false)] public static extern IntPtr memcpy(IntPtr dest, IntPtr src, UIntPtr count); unsafe static st[] Read(string path) { using (var file = File.OpenRead(path)) { int size = sizeof(st); const int BLOCK_SIZE = 512; // process at a time byte[] buffer = new byte[BLOCK_SIZE * size]; UIntPtr bufferLen = new UIntPtr((uint)buffer.Length); fixed (byte* bufferPtr = buffer) { Fill(file, buffer, 0, 4); int len = ((int*)bufferPtr)[0]; st[] result = new st[len]; fixed (st* dataPtr = result) { st* rawPtr = dataPtr; IntPtr source= new IntPtr(bufferPtr); while (len &gt;= BLOCK_SIZE) { Fill(file, buffer, 0, buffer.Length); memcpy(new IntPtr(rawPtr), source, bufferLen); len -= BLOCK_SIZE; rawPtr += BLOCK_SIZE; } if (len &gt; 0) { Fill(file, buffer, 0, len * size); memcpy(new IntPtr(rawPtr), source, new UIntPtr((uint)(len * size))); } } return result; } } } static void Fill(Stream source, byte[] buffer, int offset, int count) { int read; while (count &gt; 0 &amp;&amp; (read = source.Read(buffer, offset, count)) &gt; 0) { offset += read; count -= read; } if (count &gt; 0) throw new EndOfStreamException(); } unsafe static void Write(st[] data, string path) { using (var file = File.Create(path)) { int size = sizeof(st); const int BLOCK_SIZE = 512; // process at a time byte[] buffer = new byte[BLOCK_SIZE * size]; int len = data.Length; UIntPtr bufferLen = new UIntPtr((uint)buffer.Length); fixed (st* dataPtr = data) fixed (byte* bufferPtr = buffer) { // write the number of elements ((int*)bufferPtr)[0] = data.Length; file.Write(buffer, 0, 4); st* rawPtr = dataPtr; IntPtr destination = new IntPtr(bufferPtr); // write complete blocks of BLOCK_SIZE while (len &gt;= BLOCK_SIZE) { memcpy(destination, new IntPtr(rawPtr), bufferLen); len -= BLOCK_SIZE; rawPtr += BLOCK_SIZE; file.Write(buffer, 0, buffer.Length); } if (len &gt; 0) { // write an incomplete block, if necessary memcpy(destination, new IntPtr(rawPtr), new UIntPtr((uint)(len * size))); file.Write(buffer, 0, len * size); } } } } </code></pre>
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    1. POProcessing a large file in .NET
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    1. USMarc Gravell
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    1. POProcessing a large file in .NET
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    1. CO+1, single sync thread for file write is the way to go.
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    2. COI think writing in a single thread would be fine too, I'm more concerned about the reading... why would I need to lock anything? Isn't the FileStream.SomethingAsync use Completion ports?
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    3. CO@AK_ a file can only be at one position; you need to know that you're reading/writing contiguous parts of the file; added full read/write implementation, btw
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