问题
My application runs SQL Server 2008 on Windows Server 2008 using Tomcat.
I am using a Cloud-based server
One of my queries takes exactly 48 seconds to run from the application. It pulls 425 records from the database.
I was not surprised by the length of time.
Although a similar query on Oracle ran in 6 seconds, the Oracle setup had 2GB of memory and a quad-processor, whereas my SQL Server set up was 1GB of memory and a single 2.66GHZ processor.
Therefore I increased my server spec to 2GB. There was no change.
I then increased my server spec to dual processor from single processor. I was surprised to find that the query now took longer - exactly 70 seconds!
I am aware that the conversion of the query from P/SQL to T/SQL may have been done in a very non-efficient way. And there may be speed differences between Oracle and SQL Server. However my main question is really, why should the same query now run slower on a dual-core system than on a single-core?
Thank you!
回答1:
Depending on the hypervisor used and the total load on the server, dual virtual CPUs can result in getting (significantly) less CPU time, as some hypervisor's scheduler insists of finding 2 CPUs that are schedulable at the same time. If your query is single-threaded, the advantage of a second CPU is zero, but getting less CPU time makes it slower.
Exactly the opposite direction is another possibility: If your query is multithreaded and your storage is slow, then the 2 threads can create a random IO storm, that decreases your storage throughput.
来源：https://stackoverflow.com/questions/8926005/my-cloud-based-server-runs-a-sql-server-query-50-slower-after-an-upgrade-to-dua