自适应哈希索引引起的不定时MySQL崩溃重启
我们先看一下这个报错日志：InnoDB:Warning:alongsemaphorewait:--Thread140593224754944haswaitedatbtr0cur.cline528for241.00secondsthesemaphore:X-lockonRW-
我们先看一下这个报错日志：
这台机器凌晨MySQL进程崩溃，错误日志里全都是
InnoDB: Warning: a long semaphore wait
--Thread 140570431108864 has waited at btr0cur.c line 528 for 241.00 seconds the semaphore:
X-lock on RW-latch at 0x7fd9142bfcc8 created in file dict0dict.c line 1838
查看监控图（参考25日至31日）
发现spin waits和OS waits等待时间相当高，，在手册里查到了这一句话：
You can monitor the use of the adaptive hash index and the contention for its use in the SEMAPHORES section of the output of the SHOW ENGINE INNODB STATUS command. If you see many threads waiting on an RW-latch created in btr0sea.c, then it might be useful to disable adaptive hash indexing.由于自适应哈希索引造成大量的锁争用，进而堵塞很多进程，最终导致MySQL崩溃重启。
找到原因后，关闭了自适应哈希索引，观察了一天后（参考性能图1月1日），spin waits和OS waits等待时间逐渐减少。
set global innodb_adaptive_hash_index = 0;最终病因找到解决之。
参考手册：
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