从SQL数据库缓慢加载某些数据

Question

We have a website that is taking a long time to download certain data on 4G network. It is able to load a large list of customers and all of their details very quickly from the database. But loading only a few details on a customer's last activity from another table in the database is taking a very long time (5-6 seconds to load only 6 database fields).

A sample SQL Query:

SELECT TOP(1) EventID,  StartOnDate, Description, Fullname,  ForeColor, BackColor,  WhatHappened
FROM qryCustomerHistory WHERE CustomerID=610376 AND StartOnDate < '2/21/2014' 
ORDER BY StartOnDate DESC

Our site is a .net 4.5 website displaying the data in a boostrap modal popup window. The database is Microsoft SQL Server 2012. Both the website and database are on the same Virtual Machine hosted on Windows Azure.

Answer 1

It would be hard to guess what's the root cause.

Maybe you're table contains lots of data and if so, you need a composite index containing CustomerID and StartOnDate to speed up the table scan.

Also whatever comes in Order by clause generally needs an index.

You must trace the request both on client side and server side to be sure what's the problem.

You can user Developer Tools of almost any recent browser to trace the request on client side (checkout firebug network monitoring ).

For the server side, user profiling tools or debug level logging of a logging framework like NLog or Log4net.