• Resource Waits - time spent waiting for a resource to be available e.g. Locks, Latches, I/O etc

• Signal Waits - the equivalent of the UNIX run queue - time spent waiting for the CPU to become available (as opposed to time spent actually processing)

• Queue Waits - time spent waiting for something to do

• External Waits - time spent waiting for something outside the database

"Posion" Waits

CXCONSUMER

CXPACKET

If it doesn't need to wait for anything else, a SQL Server thread will run for a maximum of 4ms then voluntarily yield the processor. High SOS_SCHEDULER_YIELD waits can be an indicator of a SQL Server where all other waits have been eliminated. However, in a virtual environment, they can also be an indicator of hypervisor performance problems (i.e. cpu contention - check RDY%).