After a lot more testing, the latency I am experiencing is consistent and not sensitive to the buffer size. I am accepting this as a limitation of FileTable and it being less than ideal for very chatty IO.
SQL Server 2012 FileTable Slow Performance when Creating File (Integrating Lucene.NET)
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29-06-2022 - |
Question
I have been prototyping an approach to integrating Lucene.NET with SQL Server using SQL Server FileTable. The usage is very convenient and the code is simple - I don't have to do anything special with customizing Lucene.NET. The advantage I seek is mostly operational and enterprisey - my Company operates SQL Server 24/7 and keeping the search index in the same control space has a lot of advantages for us (...and I do realize I won't get precise transactional consistency, that is OK).
Problem: No matter what I do, there seems to be approximately 200 milliseconds (+- 20-30ms) of overhead when writing to a file in the SQL FileTable UNC share using the WinAPI (via System.IO.FileStream). This is significant with Lucene.NET because an index write operation directly to my local file system takes ~50ms, whereas the same operation to the FileTable takes ~2-3 seconds!
To sanity check this, I created another experiment that writes 3 new (create) files at 10KB, 1MB and 10MB. I wrote these 3 files to:
- A local directory (
c:\Search\\
) - A non-FileTable share via UNC Path (
\\\127.0.0.1\\Search\\
) - A FileTable UNC path (
\\\127.0.0.1\[instance-share]\\search_index\\
)
Using System.Diagnostics.Stopwatch
, writing to the local directory was fastest as expected, writing to the non-FileTable share was slower but comparable, and the FileTable was an order of magnitude slower. What was interesting is the 2 larger file sizes performed similarly in case 2 and 3, which leads me to believe the overhead with file creation levels the timings.
Question: Does anyone have deeper insight into why file creation with FileTable is so "slow"?
This is a development VM with little concurrent activity (4GB RAM, 2 vCPU, probably some IO contention but these tests are meant to be relative comparisons). Insert into SQL Server for a trivial row on this box barely hits 1ms.
I don't have the code handy but will post with an edit soon (with exact timings) - it is very simple and just writes 4K chunks of a statically initialized byte array in a loop to the desired size.
I did implement the following recommendations, and also tuned the SMB stack, with no difference in performance: http://blogs.msdn.com/b/blogdoezequiel/archive/2011/02/11/best-practices-on-filestream-implementations.aspx#.UkbEYtKshcZ
EDIT: Timings from output test console:
Writing files for directory: c:\Search
Writing file size : 10240
Writing file size : 1048576
Writing file size : 10485760
Writing files for directory: \\127.0.0.1\Search
Writing file size : 10240
Writing file size : 1048576
Writing file size : 10485760
Writing files for directory: \\127.0.0.1\Sql2012\FIndex\search_index
Writing file size : 10240
Writing file size : 1048576
Writing file size : 10485760
Write Timings
---------------------------------------------------------------
Paths (rows): Local, Shared, SQL File Table
Sizes (columns): 10KB, 1MB, 10MB
---------------------------------------------------------------
Local: 3 2 17
Share: 28 31 64
FTable: 205 249 317
Source Code (very simple, posted for completeness): Console Main with ASCII art omitted:
private static readonly string[] paths = new string[]
{
@"c:\Search",
@"\\127.0.0.1\Search",
@"\\127.0.0.1\Sql2012\FIndex\search_index"
};
private static readonly int[] sizes = new int[]
{
1024 * 10,
1024 * 1024,
1024 * 1024 * 10
};
static void Main(string[] args)
{
// Directory: Size 1, 2, 3
var timings = new long[3, 3];
var stopwatch = new Stopwatch();
for(var x = 0; x < 3; x++)
{
Console.WriteLine("Writing files for directory: {0}", paths[x]);
for(var y = 0; y < 3; y++)
{
Console.WriteLine("\tWriting file size : {0}", sizes[y]);
string fileName = Path.Combine(paths[x], Guid.NewGuid().ToString() + ".bin");
stopwatch.Start();
FileIOTestHelper.WriteFile(fileName, sizes[y]);
stopwatch.Stop();
timings[x, y] = stopwatch.ElapsedMilliseconds;
stopwatch.Reset();
}
}
// ascii art display code
}
Implementation class:
public static class FileIOTestHelper
{
private static readonly byte[] testBuffer = CreateBuffer();
private static byte[] CreateBuffer()
{
var buffer = new byte[4096];
for (var i = 0; i < 4096; i++)
{
buffer[i] = (byte)(i % 256);
}
ForceIOJit(buffer);
return buffer;
}
private static void ForceIOJit(byte[] initBuffer)
{
// Shouldn't matter, but eliminating any possible warm up cost.
using (var fs = new FileStream(Path.GetTempFileName(), FileMode.Open))
{
fs.Write(initBuffer, 0, 4096);
fs.Flush();
}
}
public static void WriteFile(string name, int sizeInBytes)
{
var count = sizeInBytes / 4096;
var remainder = sizeInBytes % 4096;
using (var fs = new FileStream(name, FileMode.Create))
{
for (int i = 0; i < count; i++)
{
fs.Write(testBuffer, 0, 4096);
}
if (remainder > 0)
{
fs.Write(testBuffer, 0, remainder);
}
fs.Flush();
}
}
}
Solution