C# – Memcached/Microsoft Velocity Performance Question

appfabriccmemcachedsql

Just a random query regarding Microsoft Velocity.

Scenario:
Say I want ALL Orders from my database. In SQL, this is fine, I can do SELECT OrderId,TotalCost... from Orders. This is one round trip to my database, and everyone is happy.

Now, if I'm using Memcached or (as I'm using now) Microsoft Velocity (CTP3), there is no easy way to do this. The two options I see are (in pseudo code)

FOR EACH ORDER
     Order = cache.TryGet(OrderId)
     if Order is null
            Order = db.Get(OrderId)
END FOR EACH

which would be LOADS of roundtrips.

Also, consider I want to get orders by Customer

SQL: Select OrderId....TotalCost from Orders where CustomerId = MyCustomerId

One round trip, everyone is happy.

Using a cached solution there are two solutions I see really:

Solution 1:

DOES CustomerOrderIdsForCustomerId EXIST
     NO
           POPULATE CustomerOrderIdsForCustomerId FROM DATABASE
     YES
           FOR EACH OrderId IN CustomerOrdersForCustomerId
                  cache.TryGet(OrderId)
                  IF Order IS NULL
                        Order = db.Get(OrderId)
           END FOR EACH

Solution 2 is to hold a serialized list of all the customer orders in it's own cache object. Reduces round trips, but just seems lame.

Can someone shed light on this situation please?

Best Answer

Just because you have a cache doesn't mean you have to use it for every query! In this instance as you've already identified, it's not really helping you and I'd probably go straight through to the database for this sort of thing.
It depends a bit on your application though - if you think customers are regularly going to be looking at their order history, or you have some function that's analysing orders to see what products are hot, then you might want to use some caching to keep load off your SQL server. In that case, I'd probably go with holding in the cache either a DataTable of the orders, or a collection of Orders and query it with LINQ to show the orders for a customer.

Related Solutions

C# – How to create an Excel (.XLS and .XLSX) file in C# without installing Microsoft Office

You can use a library called ExcelLibrary. It's a free, open source library posted on Google Code:

ExcelLibrary

This looks to be a port of the PHP ExcelWriter that you mentioned above. It will not write to the new .xlsx format yet, but they are working on adding that functionality in.

It's very simple, small and easy to use. Plus it has a DataSetHelper that lets you use DataSets and DataTables to easily work with Excel data.

ExcelLibrary seems to still only work for the older Excel format (.xls files), but may be adding support in the future for newer 2007/2010 formats.

You can also use EPPlus, which works only for Excel 2007/2010 format files (.xlsx files). There's also NPOI which works with both.

There are a few known bugs with each library as noted in the comments. In all, EPPlus seems to be the best choice as time goes on. It seems to be more actively updated and documented as well.

Also, as noted by @АртёмЦарионов below, EPPlus has support for Pivot Tables and ExcelLibrary may have some support (Pivot table issue in ExcelLibrary)

Here are a couple links for quick reference:
ExcelLibrary - GNU Lesser GPL
EPPlus - GNU (LGPL) - No longer maintained
EPPlus 5 - Polyform Noncommercial - Starting May 2020
NPOI - Apache License

Here some example code for ExcelLibrary:

Here is an example taking data from a database and creating a workbook from it. Note that the ExcelLibrary code is the single line at the bottom:

//Create the data set and table
DataSet ds = new DataSet("New_DataSet");
DataTable dt = new DataTable("New_DataTable");

//Set the locale for each
ds.Locale = System.Threading.Thread.CurrentThread.CurrentCulture;
dt.Locale = System.Threading.Thread.CurrentThread.CurrentCulture;

//Open a DB connection (in this example with OleDB)
OleDbConnection con = new OleDbConnection(dbConnectionString);
con.Open();

//Create a query and fill the data table with the data from the DB
string sql = "SELECT Whatever FROM MyDBTable;";
OleDbCommand cmd = new OleDbCommand(sql, con);
OleDbDataAdapter adptr = new OleDbDataAdapter();

adptr.SelectCommand = cmd;
adptr.Fill(dt);
con.Close();

//Add the table to the data set
ds.Tables.Add(dt);

//Here's the easy part. Create the Excel worksheet from the data set
ExcelLibrary.DataSetHelper.CreateWorkbook("MyExcelFile.xls", ds);

Creating the Excel file is as easy as that. You can also manually create Excel files, but the above functionality is what really impressed me.

C# – What do two question marks together mean in C#

It's the null coalescing operator, and quite like the ternary (immediate-if) operator. See also ?? Operator - MSDN.

FormsAuth = formsAuth ?? new FormsAuthenticationWrapper();

expands to:

FormsAuth = formsAuth != null ? formsAuth : new FormsAuthenticationWrapper();

which further expands to:

if(formsAuth != null)
    FormsAuth = formsAuth;
else
    FormsAuth = new FormsAuthenticationWrapper();

In English, it means "If whatever is to the left is not null, use that, otherwise use what's to the right."

Note that you can use any number of these in sequence. The following statement will assign the first non-null Answer# to Answer (if all Answers are null then the Answer is null):

string Answer = Answer1 ?? Answer2 ?? Answer3 ?? Answer4;

Also it's worth mentioning while the expansion above is conceptually equivalent, the result of each expression is only evaluated once. This is important if for example an expression is a method call with side effects. (Credit to @Joey for pointing this out.)

Best Answer

Related Solutions

C# – How to create an Excel (.XLS and .XLSX) file in C# without installing Microsoft Office

C# – What do two question marks together mean in C#

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