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mysql提示Writing to net解决
最近发现某一个数据库cpu占用比较过。超过200%了。
首先查看数据库慢日志，设定慢日志5秒，基本上没有产生日，没有超过5秒的语句。
show processlist;
后发现几条select有几个表查询需要1-2秒，
explain select * from xxx ，发现没有走索引，全表扫描，以前数据量少那会很快就出来了，目前查询总数据都在2万以内，现在数据量大了，其它表都1000w级了，以前只优化了大表的索引，所以问题就突出了。索引建完后CPU明显示下降，据我了解，msyql cpu占用高，80%的情况未使用索引有关。
在次show processlist
发现多条语句状态为Writing to net
通过分析基本都是select 语句，都是查询数据太数据库返回网络回写不赢，
查看show global variables like "global max_allowed_packet" 只有1M
通过增加缓存
set global max_allowed_packet =134217728
问题得到解决！原因是多条select 返回数据越过缓存超过默认设置。
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