In mongodb i work with this collection:
Size 55.93g Data Size 39.82g Storage Size 41.08g Extents 53 Indexes 4 Index Size 9.64g
It takes few seconds of mongdb being up with this single collection and all 48GB RAM on the dedicated server are gone.
That's worse because there is also a mysqld+nginx/fcgi on this machine which should be allowed to use at least 24GB together. I.e. remaining 24GB, enough for the mongod!
However, it does not share in a fair way. Everybody says that the memory for mongod is managed by OS and releases unneccessary space for other processes if they demand RAM. On my machine it is not releasing RAM. What's wrong?
total used free shared buffers cached` Mem: 49559136 49403908 155228 0 57284 47247564 -/+ buffers/cache: 2099060 47460076 Swap: 8008392 164 8008228