[ewb]

"But I guess you could dump old data to disk and load it back to Redis only when you need it."

Redis has a mode which does this automatically I believe (and it's the default if I remember correctly).

[Erwin]

Isn't Redis still single-threaded for queries, but saving in the background? That seems a little risky: you've got your 100 million users setting bits in your bitsets and suddenly everything blocks for 10 seconds while old data is being loaded from disk.

[kijin]

The "virtual memory" feature is now deprecated, I think.