SQL Server等待事件新解

资源等待类型

并行：CXPACKET

Buffer：PAGEIOLATCH_X

非Buffer：LATCH_X

I/O：ASYNC_IO_COMPITION；IO_COMPITION

CPU：SOS_SCHEDULER_YIELD

日志：WRITELOG&LOGBUFFER   
  锁阻塞：LCK_*

内存：RESOURCE_SEMAPHORE

外部：PREEMPTIVE_XXX

备份：DISKIO_SUSPENDE

等待事件： ASYNC_NETWORK_IO

 清空当前等待事件统计  ：  DBCC SQLPERF ('sys.dm_os_wait_stats', CLEAR);

说明：  该SQL查询有查出大量的数据行或者是大量数据，如（text 或者 varchar(max) 字段）

等待事件： HADR_SYNC_COMMIT

说明： 实时备库可能有很耗CPU的sql

等待事件： WRITELOG

说明： 数据库的写入量比较大

等待事件： LATCH_EX [ACCESS_METHODS_DATASET_PARENT]

说明：查询没有索引，需要回表查数据

LATCH_EX：Exclusive Latch，表明数据正在被改变或添加。两个EX Latch不能同时保留在用一个页上

查看sys.dm_os_wait_stats的内容，你会看到LATCH_, PAGELATCH_ 和PAGEIOLATCH_打头的Latch，

其中LATCH_打头的等待都是用于Non-BUF类型，

PAGELATCH_打头的Latch应用于各种页，

PAGEIOLATCH_打头的Latch用于数据从磁盘移到RAM。

Other information:

A latch is a lightweight synchronization mechanism that provides synchronization between threads trying to read or change a data structure in SQL Server. There are three types of latches:

• Latches on pages being read from disk (these are covered by the PAGEIOLATCH_XX wait types – see the PAGEIOLATCH_SH wait type for more details)
• Latches on pages already in memory (these are covered by the PAGELATCH_XX wait types – see the PAGELATCH_EX wait type for more details)
• Latches on non-page data structures (i.e. everything else)

The LATCH_SH and LATCH_EX wait types occur when a thread requires access to a non-page data structure (e.g., page buffers in the buffer pool (latch type = BUFFER), or the data structure that represents a database’s data and log files (latch type = FGCB_ADD_REMOVE)).

https://blog.csdn.net/burgess_liu/article/details/19607151