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多mysql实例下开发需要注意主从同步延迟
今天晚上服务器上线测试，遇到了一个问题！
往数据库写了一条数据之后，再读取该记录，居然读不出来，报空指针。十分费解，喊来开发组长定位问题。他的解释是：写操作用的是主库，而读操作用的是从库。在写库写完之后，该条记录并不会立刻出现在读库，数据同步到写库需要一定的时间。于是出现了我的空指针异常。
回来看了很多网上的介绍主从同步机制。大致是这样的，主库执行完sql写命令之后，将日志写至binlog。从库有一个线程会拉取主库上的这个日志文件，获取新的数据写操作日志。并将拉取到的日志写至本机的relay-log。从库的sql线程会从本机的relay-log中
取出日志，并执行。至此，同步完成。可以看出主从间同步是需要一些时间的。
好的士兵不会跳进同一个陷阱。以后遇到类似的问题，正确的做法是，如需要写完数据立刻查该数据，则需要用主库（写库）查，而非从库（读库）。分享下我的经验，希望对大家有用。
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