MongoDb C＃驱动程序-通过索引字段获取项目非常慢

Question

I ran into performance issues when fetching filtered data on a small local database. I reduced the code (as below) to reproduce the issue. The output is about 2000ms.

Some additional information:

• The queried collection contains 135,000 entries with 7 simple types each
  
• When running a similar query in something like RoboMongo - db.TickerData.find({_id : ObjectId('5731d39062deb83134772e77')}).explain() - the totalExecutionTime is <1ms
• I am using the latest MongoDb server and C# driver versions
  
• The database is running locally (quad core 16Mb Ram) on the same dev/debug environment
  
• I noticed no difference in performance between indexed and non indexed fields when testing on other fields than the ID (which is always indexed)
  
• My first though was that the .Single() linq operation retrieves all the documents before doing a single search but from Google'ing it seems that all linq operations is transposed to MongoDB server side queries
  

Code:

public class UnitTest1
{
    public void TestMethod2()
    {
        Stopwatch sw = new Stopwatch();
        sw.Start();
        new BaseRepository<TickerData>().GetById("5731d39062deb83134772e77");
        sw.Stop();
        Debug.Write(sw.Elapsed.TotalMilliseconds);
    }
}

public class BaseRepository<T> : MongoBase where T : BaseEntity
{
    MongoDatabase DataBase { get; set; }
    protected IQueryable<T> Collection { get; set; }
    MongoCollection<BsonDocument> mCollection { get; set; }

    public BaseRepository()
    {
        DataBase = Server.GetDatabase("TradingBot");
        mCollection = DataBase.GetCollection<BsonDocument>(typeof(T).Name);
        Collection = mCollection.AsQueryable<T>();
    }

    public T GetById(string ID)
    {
        return Collection.Single(i => i.Id.ToString() == ID);
    }

}

Update: Suggest as per @rnofenko (see comments) made a huge improvement but still seem way to slow?

Answer 1

It's a tricky moment. You call extension method Single from System.Linq . In fact you load whole collection from DB and select by ID inside your application.

Instead you need to use MongoDB extension method - SingleAsync from MongoDB.Driver.Linq .

public async Task<T> GetById(string id)
{
    return await Collection.SingleAsync(x => x.Id == new ObjectId(id));
}