无法在后台保存(redis-server)

Background saving is failing with a fork() error under Linux even if I’ve a lot of free RAM!

Short answer: echo 1 > /proc/sys/vm/overcommit_memory

And now the long one:

Redis background saving schema relies on the copy-on-write semantic of

fork in modern operating systems: Redis forks (creates a child

process) that is an exact copy of the parent. The child process dumps

the DB on disk and finally exits. In theory the child should use as

much memory as the parent being a copy, but actually thanks to the

copy-on-write semantic implemented by most modern operating systems

the parent and child process will share the common memory pages. A

page will be duplicated only when it changes in the child or in the

parent. Since in theory all the pages may change while the child

process is saving, Linux can’t tell in advance how much memory the

child will take, so if the overcommit_memory setting is set to zero

fork will fail unless there is as much free RAM as required to really

duplicate all the parent memory pages, with the result that if you

have a Redis dataset of 3 GB and just 2 GB of free memory it will

fail. Setting overcommit_memory to 1 says Linux to relax and perform

the fork in a more optimistic allocation fashion, and this is indeed

what you want for Redis.