When should I call SaveChanges() when creating 1000's of Entity Framework objects? (like during an import)

Question

I am running an import that will have 1000's of records on each run. Just looking for some confirmation on my assumptions:

Which of these makes the most sense:

1. Run SaveChanges() every AddToClassName() call.
2. Run SaveChanges() every n number of AddToClassName() calls.
3. Run SaveChanges() after all of the AddToClassName() calls.

The first option is probably slow right? Since it will need to analyze the EF objects in memory, generate SQL, etc.

I assume that the second option is the best of both worlds, since we can wrap a try catch around that SaveChanges() call, and only lose n number of records at a time, if one of them fails. Maybe store each batch in an List<>. If the SaveChanges() call succeeds, get rid of the list. If it fails, log the items.

The last option would probably end up being very slow as well, since every single EF object would have to be in memory until SaveChanges() is called. And if the save failed nothing would be committed, right?

Answer 1

I would test it first to be sure. Performance doesn't have to be that bad.

If you need to enter all rows in one transaction, call it after all of AddToClassName class. If rows can be entered independently, save changes after every row. Database consistence is important.

Second option I don't like. It would be confusing for me (from final user perspective) if I made import to system and it would decline 10 rows out of 1000, just because 1 is bad. You can try to import 10 and if it fails, try one by one and then log.

Test if it takes long time. Don't write 'propably'. You don't know it yet. Only when it is actually a problem, think about other solution (marc_s).

EDIT

I've done some tests (time in miliseconds):

10000 rows:

SaveChanges() after 1 row:18510,534
SaveChanges() after 100 rows:4350,3075
SaveChanges() after 10000 rows:5233,0635

50000 rows:

SaveChanges() after 1 row:78496,929
SaveChanges() after 500 rows:22302,2835
SaveChanges() after 50000 rows:24022,8765

So it is actually faster to commit after n rows than after all.

My recommendation is to:

• SaveChanges() after n rows.
• If one commit fails, try it one by one to find faulty row.

Test classes:

TABLE:

CREATE TABLE [dbo].[TestTable](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [SomeInt] [int] NOT NULL,
    [SomeVarchar] [varchar](100) NOT NULL,
    [SomeOtherVarchar] [varchar](50) NOT NULL,
    [SomeOtherInt] [int] NULL,
 CONSTRAINT [PkTestTable] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

Class:

public class TestController : Controller
{
    //
    // GET: /Test/
    private readonly Random _rng = new Random();
    private const string _chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    private string RandomString(int size)
    {
        var randomSize = _rng.Next(size);

        char[] buffer = new char[randomSize];

        for (int i = 0; i < randomSize; i++)
        {
            buffer[i] = _chars[_rng.Next(_chars.Length)];
        }
        return new string(buffer);
    }


    public ActionResult EFPerformance()
    {
        string result = "";

        TruncateTable();
        result = result + "SaveChanges() after 1 row:" + EFPerformanceTest(10000, 1).TotalMilliseconds + "<br/>";
        TruncateTable();
        result = result + "SaveChanges() after 100 rows:" + EFPerformanceTest(10000, 100).TotalMilliseconds + "<br/>";
        TruncateTable();
        result = result + "SaveChanges() after 10000 rows:" + EFPerformanceTest(10000, 10000).TotalMilliseconds + "<br/>";
        TruncateTable();
        result = result + "SaveChanges() after 1 row:" + EFPerformanceTest(50000, 1).TotalMilliseconds + "<br/>";
        TruncateTable();
        result = result + "SaveChanges() after 500 rows:" + EFPerformanceTest(50000, 500).TotalMilliseconds + "<br/>";
        TruncateTable();
        result = result + "SaveChanges() after 50000 rows:" + EFPerformanceTest(50000, 50000).TotalMilliseconds + "<br/>";
        TruncateTable();

        return Content(result);
    }

    private void TruncateTable()
    {
        using (var context = new CamelTrapEntities())
        {
            var connection = ((EntityConnection)context.Connection).StoreConnection;
            connection.Open();
            var command = connection.CreateCommand();
            command.CommandText = @"TRUNCATE TABLE TestTable";
            command.ExecuteNonQuery();
        }
    }

    private TimeSpan EFPerformanceTest(int noOfRows, int commitAfterRows)
    {
        var startDate = DateTime.Now;

        using (var context = new CamelTrapEntities())
        {
            for (int i = 1; i <= noOfRows; ++i)
            {
                var testItem = new TestTable();
                testItem.SomeVarchar = RandomString(100);
                testItem.SomeOtherVarchar = RandomString(50);
                testItem.SomeInt = _rng.Next(10000);
                testItem.SomeOtherInt = _rng.Next(200000);
                context.AddToTestTable(testItem);

                if (i % commitAfterRows == 0) context.SaveChanges();
            }
        }

        var endDate = DateTime.Now;

        return endDate.Subtract(startDate);
    }
}