Common Significant Wait types with BOL explanations

                                                          WaitTypes 

Network Related Waits

       ASYNC_NETWORK_IO :Occurs on network writes when the task is blocked behind the network

 Locking Waits

1. LCK_M_IX: Occurs when a task is waiting to acquire an Intent Exclusive (IX) lock.

2. LCK_M_IU: Occurs when a task is waiting to acquire an Intent Update (IU) lock.

3. LCK_M_S: Occurs when a task is waiting to acquire a Shared lock.

I/O Related Waits

1.ASYNC_IO_COMPLETION: Occurs when a task is waiting for I/Os to finish.

2. IO_COMPLETION: Occurs while waiting for I/O operations to complete.              This wait type generally represents non-data page I/Os. Data page I/O completion waits appear  as

 PAGEIOLATCH waits

3. PAGEIOLATCH_SH:Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Shared mode. Long waits may indicate problems with the disk subsystem.

4. PAGEIOLATCH_EX:Occurs when a task is waiting on a latch for a buffer that is in an I/O request.  The latch request is in Exclusive mode. Long waits may indicate problems with the disk subsystem.

5. WRITELOG : Occurs while waiting for a log flush to complete. Common operations that cause log flushes are checkpoints and transaction commits.

6. PAGELATCH_EX: Occurs when a task is waiting on a latch for a buffer that is not in an I/O request. The latch request is in Exclusive mode.

7. BACKUPIO:Occurs when a backup task is waiting for data, or is waiting for a buffer in which to store data

CPU Related Waits

1. SOS_SCHEDULER_YIELD:  Occurs when a task voluntarily yields the scheduler for other tasks to execute. During this wait the task is waiting for its quantum to be renewed.

2. THREAD POOL : Occurs when a task is waiting for a worker to run on.

  This can indicate that the maximum worker setting is too low, or that batch executions are taking  unusually long, thus reducing the number of workers available to satisfy other batches.

3. CX_PACKET: Occurs when trying to synchronize the query processor exchange iterator .You may consider lowering the degree of parallelism if contention on this wait type becomes a problem.