redis : Can't save in background: fork: Cannot allocate memory
专注于为中小企业提供成都网站建设、成都网站设计服务,电脑端+手机端+微信端的三站合一,更高效的管理,为中小企业海淀免费做网站提供优质的服务。我们立足成都，凝聚了一批互联网行业人才，有力地推动了上千多家企业的稳健成长，帮助中小企业通过网站建设实现规模扩充和转变。
JAVA程序报错信息：
MISCONF Redis is configured to save RDB snapshots, but is currently not able to persist on disk. Commands that may modify the data set are disabled. Please check Redis logs for details about the error
查看redis日志：
18793:S 02 Dec 10:02:02.069 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:02:08.088 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:02:14.006 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:02:20.021 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:02:26.038 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:02:32.054 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:02:38.067 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:02:44.086 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:02:50.002 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:02:56.017 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:03:02.037 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:03:08.056 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:03:14.073 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:03:20.091 # Can't save in background: fork: Cannot allocate memory
18793:S 02 Dec 10:03:26.007 # Can't save in background: fork: Cannot allocate memory
数据回写分同步和异步两种方式:
同步回写(SAVE), 主进程直接向磁盘回写数据. 在数据量大的情况下会导致系统假死很长时间
异步回写(BGSAVE), 主进程fork后, 复制自身并通过这个新的进程回写磁盘, 回写结束后新进程自行关闭
由于 BGSAVE 不需要主进程阻塞, 系统也不会假死, 一般会采用 BGSAVE 来实现数据回写.
redis在dump数据的时候会启动fork子进程，由于内存不够，导致无法持久化落盘
redis有个默认的选项：
stop-writes-on-bgsave-error yes
这个选项默认情况下，如果在RDB snapshots持久化过程中出现问题，设置该参数后，Redis是不允许用户进行任何更新操作。
不彻底的解决方式是，将这个选项改为false
stop-writes-on-bgsave-error false
但是这样只是当redis写硬盘快照出错时，可以让用户继续做更新操作，但是写硬盘仍然是失败的
彻底解决方案：直接修改内核参数 vm.overcommit_memory = 1
编辑文件 /etc/sysctl.conf 添加：
vm.overcommit_memory=1
执行sysctl -p使其生效
Linux内核会根据参数vm.overcommit_memory参数的设置决定是否放行。
vm.overcommit_memory = 1，直接放行
vm.overcommit_memory = 0：则比较 此次请求分配的虚拟内存大小和系统当前空闲的物理内存加上swap，决定是否放行。
vm.overcommit_memory = 2：则会比较进程所有已分配的虚拟内存加上此次请求分配的虚拟内存和系统当前的空闲物理内存加上swap，决定是否放行。
本文标题：redis:Can'tsaveinbackground:fork:Cannotallocatememory
网站URL：
http://cdkjz.cn/article/jcjhpe.html
