Question

I started an ASP.NET project with Entity Framework 4 for my DAL, using SQL Server 2008. In my database, I have a table Users that should have many rows (5.000.000 for example).

Initially I had my Users table designed like this:

Id  uniqueidentifier    
Name    nvarchar(128)   
Password    nvarchar(128)
Email   nvarchar(128)
Role_Id int 
Status_Id   int

I’ve modified my table, and added a MarkedForDeletion column:

Id  uniqueidentifier    
Name    nvarchar(128)   
Password    nvarchar(128)
Email   nvarchar(128)
Role_Id int 
Status_Id   int 
MarkedForDeletion   bit

Should I delete every entity each time, or use the MarkedForDeletion attribute. This means that I need to update the value and at some moment in time to delete all users with the value set to true with a stored procedure or something similar.

Wouldn’t the update of the MarkedForDeletion attribute cost the same as a delete operation?

Answer 1

Depending on the requirements/needs/future needs of your system, consider moving your ‘deleted’ entities over to a new table. Setup an ‘audit’ table to hold those that are deleted. Consider the case where someone wants something ‘restored’.

To your question on performance: would the update be the same cost as a delete? No. The update would be a much lighter operation, especially if you had an index on the PK (errrr, that’s a guid, not an int). The point being that an update to a bit field is much less expensive. A (mass) delete would force a reshuffle of the data. Perhaps that job belongs during a downtime or a low-volume period.

Regarding performance: benchmark it to see what happens! Given your table with 5 million rows, it’d be nice to see how your SQL Server performs, in its current state of indexes, paging, etc, with both scenarios. Make a backup of your database, and restore into a new database. Here you can sandbox as you like. Run & time the scenarios:

• mass delete vs.
• update a bit or smalldatetime field vs.
• move to an audit table

In terms of books, try:

• this answer re: books
• a recommendation for Adam Mechanic’s book
• another question on database books.