Does extstore also use the same slab allocator that memcached does in memory? Cause if so I feel that disk usage might actually be worse than imagined due to the slab packing problems. I think the design decision to keep everything in memcached makes a lot of sense, but RocksDB seems like an odd choice for the first iteration. It’s big claim to fame is durability while achieving high performance, and it shines in situations like MyRocks, but for caching, especially where replication is handled on top of the things writing to disk, that doesn’t seem as important. I think extstore also does compaction but on a 64M page by page basis instead of using one big log.
>EVCache has become a fundamental tier-0 service storing petabytes of data and hundred of billions of items,
So newest Memcache with extstore allows them instead of PB of RAM to PB of SSD. I look at the pricing of EC2 instances, turns out it is may be a $3/hr saving between Memory Optimised and Storage I/O optimised. On a petabytes scale at 500GB / node that translate to roughly $4.3 million saving per month from on demand pricing. Likely much lower from Netflix discount but still quite a bit of money.
