SQL Server performance counters

The following table describes the default counters that can be monitored on the SQL Server:

% Total Processor Time
The average percentage of time that all the processors on the system are busy executing non-idle threads. On a multi-processor system, if all processors are always busy, this is 100%, if all processors are 50% busy this is 50% and if 1/4 of the processors are 100% busy this is 25%. It can be viewed as the fraction of the time spent doing useful work. Each processor is assigned an Idle thread in the Idle process which consumes those unproductive processor cycles not used by any other threads.
% Processor Time
The percentage of time that the processor is executing a non-idle thread. This counter was designed as a primary indicator of processor activity. It is calculated by measuring the time that the processor spends executing the thread of the idle process in each sample interval, and subtracting that value from 100%. (Each processor has an idle thread which consumes cycles when no other threads are ready to run). It can be viewed as the percentage of the sample interval spent doing useful work. This counter displays the average percentage of busy time observed during the sample interval. It is calculated by monitoring the time the service was inactive, and then subtracting that value from 100%.
Cache Hit Ratio
The percentage of time that a requested data page was found in the data cache (instead of being read from disk).
I/O - Batch Writes/sec
The number of 2K pages written to disk per second, using Batch I/O. The checkpoint thread is the primary user of Batch I/O.
I/O - Lazy Writes/sec
The number of 2K pages flushed to disk per second by the Lazy Writer.
I/O - Outstanding Reads
The number of physical reads pending.
I/O - Outstanding Writes
The number of physical writes pending.
I/O - Page Reads/sec
The number of physical page reads per second.
I/O - Transactions/sec
The number of Transact-SQL command batches executed per second.
User Connections
The number of open user connections.

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