1. Basic knowleadge about SQL Server Performance Counter
| Category | Counter | Bottlenecks |
| Memory | Memory: Pages/sec | measures te number of pages per second that are paged out from RAM to Virtual memory on the hard disk. High |
| Memory: Available Bytes | measures the amount of free physical memory on a server.<5Mb | |
| SQL Server: Buffer Manager: Buffer Cache Hit Ratio | indicates how often SQL Server accesses the buffer rather than the hard disk to get data. <90% | |
| Physical Disk : Disk Read/sec | High | |
| Physical Disk : Disk Write/sec | High | |
| Disk | Physical Disk: % Disk Time | Messure the pressure on a physical hard disk array. >55% |
| Physical Disk: Avg. Disk Queue Length | if it exceed 2 for each individual disk drive in an array. >10Min | |
| Physical Disk: % Free Space | <15%, should alert the administrator | |
| Logical Disk: % Free Space | <15%, should alert the administrator | |
| Processor | Processor: % Processor Time | >80% for continuous periods of 10Min |
| Processor: Processor Queue Length | >2 per CPU for continuous periods of 10Min | |
| Network | Network Interface: Bytes Received/sec | shows the rate at which bytes are received over each network adapter. |
| Network Interface: Bytes Sent/sec | shows the rate at which bytes are sent over each network adapter. | |
| Netwok Interface: Bytes/sec | total level of network traffic both to and from a server. | |
| Netwok Interface: Output Queue Length | shows the length of the output packet queue in packets. >2 | |
| User Connections | SQL Server: Genereal Statistics: User Connections | shows the number of user connections, not the number of users currently connected to Server |
2. Practise
There is one vitrul PC (Windows 2003 Entperise. T7500 2.2G, 256MB RAM), which hosts a SQL Server 2005.
When the SQL Server is idle, whose performance is dicated as the following figure 
When i execute the following T-SQL, whose performance is shown here: 
Then, we look up anohter case, what can you infor from it?