MISCONF Redis is configured to save RDB snapshots, but is currently not able to persist on disk

Dear 丶 2022-05-26 13:50 75阅读 0赞

redis节点所在服务器内存不够了 fork时候

转载 ：https://www.cnblogs.com/qq78292959/p/3994349.html

今天第二次遇到Redis “MISCONF Redis is configured to save RDB snapshots, but is currently not able to persist on disk”的问题。这个错误信息是Redis客户端工具在保存数据时候抛出的异常信息。

网上查了一下，很多人都是建议“config set stop-writes-on-bgsave-error no”。这样做其实是不好的，这仅仅是让程序忽略了这个异常，使得程序能够继续往下运行，但实际上数据还是会存储到硬盘失败！

上一次遇到这个问题是因为一个程序的Bug造成系统内存被耗尽了，后来修复了那个Bug问题就解决了。今天出现问题时查看系统内存还有2GB左右，“感觉好像不是内存的缘故”（后面发现还是因为内存的缘故）。

由于Redis是daemon模式运行的，没法看到详细的日志。修改配置文件设置logfile参数为文件（默认是stdout，建议以后安装完毕就修改这个参数为文件，不然会丢掉很多重要信息），重启Redis，查看日志，看到程序启动时就有一行警告提示：

“WARNING overcommit\_memory is set to 0! Background save may fail under low memory condition. To fix this issue add 'vm.overcommit\_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit\_memory=1' for this to take effect.”（警告：过量使用内存设置为0！在低内存环境下，后台保存可能失败。为了修正这个问题，请在/etc/sysctl.conf 添加一项 'vm.overcommit\_memory = 1' ，然后重启（或者运行命令'sysctl vm.overcommit\_memory=1' ）使其生效。）

当时没明白意思，就忽略了。再启动Redis客户端，程序保存数据时继续报“MISCONF Redis is configured to save RDB snapshots, but is currently not able to persist on disk”异常，再查看Redis日志，看到有这样的错误提示“Can’t save in background: fork: Cannot allocate memory”，这个提示很明显"Fork进程时内存不够用了！"（还是内存的问题）。

通过谷歌查询“Can’t save in background: fork: Cannot allocate memory”这个提示，找到了解决方法：

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1.  // 原文：http://pydelion.com/2013/05/27/redis-cant-save-in-background-fork-cannot-allocate-memory/  
2.  If you get this error  
3.    
4.  Can't save in background: fork: Cannot allocate memory  
5.    
6.  it means that your current database is bigger than memory you have. To fix the issue enable vm.overcommit\_memory:  
7.    
8.  sysctl vm.overcommit\_memory=1  
9.    
10. To have if after reboot add this line to /etc/sysctl.cnf:  
11.   
12. vm.overcommit\_memory=1

**修改vm.overcommit\_memory=1后问题果然解决了。**

为什么系统明明还剩2GB的内存，Redis会说内存不够呢？

网上查了一下，有人也遇到类似的问题，并且给出了很好的分析（详见：[http://www.linuxidc.com/Linux/2012-07/66079.htm][http_www.linuxidc.com_Linux_2012-07_66079.htm]），简单地说：Redis在保存数据到硬盘时为了避免主进程假死，需要Fork一份主进程，然后在Fork进程内完成数据保存到硬盘的操作，如果主进程使用了4GB的内存，Fork子进程的时候需要额外的4GB，此时内存就不够了，Fork失败，进而数据保存硬盘也失败了。

[view plain]: http://www.redicecn.com/html/Linux/20131125/468.html
[http_www.linuxidc.com_Linux_2012-07_66079.htm]: http://www.linuxidc.com/Linux/2012-07/66079.htm

MISCONF Redis is configured to save RDB snapshots, but is currently not able to persist on disk

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