[Mono-dev] Performance issue with DataTable.Load on "large" data sets

Nicklas Overgaard nicklas at isharp.dk
Thu Apr 7 13:29:10 EDT 2011

Hi again,

I now have a profile log, created with the new mono profiler. It shows,
that the method "EndLoadData" is using up almost all of the time (16
minutes of the 17 minutes it took to create the dump).

When looking in the file "DbDataAdapter.cs" line 355 in current GIT
head, the "BeginLoadData" and "EndLoadData" methods are called for each
iteration in the DataReader's data.

This means that for each row we add to the DataTable, the DataSet is
begin asked to enforce constraints and other stuff in the datatable.

According to MSDN:

"BeginLoadData Turns off notifications, index maintenance, and
constraints while loading data."

So would'nt it make sense to move "BeginLoad.." and "EndLoad.." out of
the loop?

Well, I'm trying it out :)

Best regards,

Nicklas Overgaard

On Thu, 2011-04-07 at 14:58 +0200, Nicklas Overgaard wrote:
> Hi mono-devers!
> I'm currently working on a rather large webproject, where we are using a
> combination of mono 2.10.1 and MySQL.
> Over the past week, I have observed that loading "large" datasets (5000+
> rows) from mysql into a DataTable takes a very long time. 
> It's done somewhat like this:
> <code>
> comm.CommandText = query;
> comm.CommandTimeout = MySQLConnection.timeout;
> MySqlDataReader reader = (MySqlDataReader)comm.ExecuteReader();
> DataTable dt = new DataTable();
> dt.Load(reader); // <- this is killing mono
> reader.Close();
> </code>
> I have created a small testprogram, compiled it on my linux machine and
> executed it.
> It takes 15 seconds to do such operation under mono - but on windows it
> takes only 0.4 seconds (with the same executable, fetching the same
> data). I have profiled the application on windows, and it seems that
> the .net framework is using specialized methods for loading data from a
> datareader.
> I have been looking through the implementation in mono, in regard to
> DataTable.Load, and I can see that a lot of validation and other stuff
> is going on, which could explain the huge difference. I'm also working
> on a mono log profile trace, to dig a little deeper.
> Would it be OK, if I tried to patch the current mono implementation to
> gain the same speeds as .net? The reason for asking, is that I know that
> I cannot contribute to Mono if I have seen the actual code in .NET (but
> does a profile result count as "seeing the code"?)
> Best regards,
> Nicklas Overgaard
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