title: Xampp mysql Error: MySQL shutdown unexpectedly
body: <p>when I starting mysql, giving the following error:</p>
  
  <pre><code>17:43:13  [mysql]   Error: MySQL shutdown unexpectedly.
  17:43:13  [mysql]   This may be due to a blocked port, missing dependencies, 
  17:43:13  [mysql]   improper privileges, a crash, or a shutdown by another method.
  17:43:13  [mysql]   Press the Logs button to view error logs and check
  17:43:13  [mysql]   the Windows Event Viewer for more clues
  17:43:13  [mysql]   If you need more help, copy and post this
  17:43:13  [mysql]   entire log window on the forums
  </code></pre>
  
  <p>then, I check the mysql_error.log:</p>
  
  <pre><code>    2017-05-03 17:39:39 202c InnoDB: Warning: Using innodb_additional_mem_pool_size is DEPRECATED. This option may be removed in        future releases, together with the option innodb_use_sys_malloc and with the InnoDB's internal memory allocator.
      170503 17:39:39 [Note] InnoDB: Using mutexes to ref count buffer pool pages
      170503 17:39:39 [Note] InnoDB: The InnoDB memory heap is disabled
      170503 17:39:39 [Note] InnoDB: Mutexes and rw_locks use Windows interlocked functions
      170503 17:39:39 [Note] InnoDB: Memory barrier is not used
      170503 17:39:39 [Note] InnoDB: Compressed tables use zlib 1.2.3
      170503 17:39:39 [Note] InnoDB: Not using CPU crc32 instructions
      170503 17:39:39 [Note] InnoDB: Initializing buffer pool, size = 16.0M
      170503 17:39:39 [Note] InnoDB: Completed initialization of buffer pool
      170503 17:39:39 [Note] InnoDB: Highest supported file format is Barracuda.
      170503 17:39:39 [Note] InnoDB: The log sequence numbers 0 and 0 in ibdata files do not match the log sequence number 1600674 in         the ib_logfiles!
      170503 17:39:39 [Note] InnoDB: Database was not shutdown normally!
      170503 17:39:39 [Note] InnoDB: Starting crash recovery.
      170503 17:39:39 [Note] InnoDB: Reading tablespace information from the .ibd files...
      170503 17:39:39 [Note] InnoDB: Restoring possible half-written data pages 
      170503 17:39:39 [Note] InnoDB: from the doublewrite buffer...
      170503 17:39:39 [Note] InnoDB: 128 rollback segment(s) are active.
      170503 17:39:39 [Note] InnoDB: Waiting for purge to start
      170503 17:39:40 [Note] InnoDB:  Percona XtraDB (http://www.percona.com) 5.6.22-72.0 started; log sequence number 1600674
      170503 17:39:40 [Note] Plugin 'FEEDBACK' is disabled.
      170503 17:39:40 [Note] Server socket created on IP: '::'.   
  </code></pre>
  
  <p>finally, I moved xampp/mysql/backup files into xampp/mysql/data and run mysql again.Then, it worked!But I don't know why.What led to this problem.</p>
  
  <p>Hope someone doubts for me！</p>