生产服务内存高问题
问题描述#
•1、“计算中心” 服务堆内存分配4g，在生产环境运行一段时间后，实际占用内存4.8G，业务运行正常，未出现OOM。（本文以此服务进行排查）
•2、生产环境的老项目，均出现运行一段时间后，内存被占满但未OOM的情况。部分实例因内存占用过高导致被系统kill，一般需要通过增加机器、实例进行解决（资源浪费）。
造成的影响#
•1、服务器物理内存15g，部署了三个服务。如实际占用内存都超过4.8g，导致服务器物理内存不够用，出现告警而将占用内存最大进程kill掉，影响生产服务的可用性，后果十分严重。
•2、如服务申请的内存超出了JVM能提供的内存大小（内存泄漏），将会导致java堆内存溢出，从而发生full gc，导致服务响应大幅度变慢，卡机等状态。
•3、在公司大促等场景的情况下，内存占用很高的服务会带来很大风险，通常需提前联系运维同事对“计算中心”进行重启，增加了开发及运维同事维护的工作量。
排查过程
代码#
（1）根据cat监控，获取“计算中心”中的热点方法，进行REVIEW，修正了部分可能会导致内存泄露的方法。并进行了观察。
（2）通过VisualVM监控，定位到部分耗时较久的操作DB热点方法，通过增加索引等方式，把查询性能控制在毫秒级。
（3）dump“计算中心”的内存镜像，通过MAT等工具观察各个对象在堆空间中所占用的内存大小、类实例数量、对象引用关系。
结论：通过以上三点，未解决和定位“计算中心”内存高问题。由此可以认为，
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