SQL Server等待事件新解

     資源等待類型 

    並行：CXPACKET 

    Buffer：PAGEIOLATCH_X 

   非Buffer：LATCH_X  

   I/O：ASYNC_IO_COMPITION；IO_COMPITION  

  CPU：SOS_SCHEDULER_YIELD

  日誌：WRITELOG&LOGBUFFER   
  鎖阻塞：LCK_* 

 內存：RESOURCE_SEMAPHORE

 外部：PREEMPTIVE_XXX

 備份：DISKIO_SUSPENDE

等待事件： ASYNC_NETWORK_IO

 清空當前等待事件統計  ：  DBCC SQLPERF ('sys.dm_os_wait_stats', CLEAR); 

       說明：  該SQL查詢有查出大量的數據行或者是大量數據，如（text 或者 varchar(max) 字段）

 

    等待事件： HADR_SYNC_COMMIT

      說明： 實時備庫可能有很耗CPU的sql

 

    等待事件： WRITELOG

      說明： 數據庫的寫入量比較大

 

    等待事件： LATCH_EX [ACCESS_METHODS_DATASET_PARENT]

     說明：查詢沒有索引，須要回表查數據

              LATCH_EX：Exclusive Latch，代表數據正在被改變或添加。兩個EX Latch不能同時保留在用一個頁上

 

      查看sys.dm_os_wait_stats的內容，你會看到LATCH_, PAGELATCH_ 和PAGEIOLATCH_打頭的Latch，

        其中LATCH_打頭的等待都是用於Non-BUF類型，

        PAGELATCH_打頭的Latch應用於各類頁，

        PAGEIOLATCH_打頭的Latch用於數據從磁盤移到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