Redis - Can data size be greater than memory size?

I'm rather new to Redis and before using it I'd like to learn some important (as for me) details on it. So....

Redis is using RAM and HDD for storing data. RAM is used as fast read/write storage, HDD is used to make this data persistant. When Redis is started it loads all data from HDD to RAM or it loads only often queried data to the RAM? What if I have 500Mb Redis storage on HDD, but I have only 100Mb or 开发者_JS百科RAM for Redis. Where can I read about it?

Redis loads everything into RAM. All the data is written to disk, but will only be read for things like restarting the server or making a backup.

There are a couple of ways you can use it with less RAM than data though. You can set it up in combination with MySQL or another disk based store to work much like memcached - you manage cache misses and persistence manually.

Redis has a VM mode where all keys must fit in RAM but infrequently accessed data can be on disk. However, I'm not sure if this is in the stable builds yet.

Recent versions (>2.0) have improved significantly and memory management is more efficient. See this blog post that explains how to use hashes to optimize RAM memory footprint: http://antirez.com/post/redis-weekly-update-7.html

The feature called Virtual Memory and it official deprecated

Redis VM is now deprecated. Redis 2.4 will be the latest Redis version featuring Virtual Memory (but it also warns you that Virtual Memory usage is discouraged). We found that using VM has several disadvantages and problems. In the future of Redis we want to simply provide the best in-memory database (but persistent on disk as usual) ever, without considering at least for now the support for databases bigger than RAM. Our future efforts are focused into providing scripting, cluster, and better persistence.

more information about VM: https://redis.io/topics/virtual-memory