People used to get filthy rich (hi there Larry) building databases (which has all sorts of data access & management goodies) until 21st century came along and in the name of "progress" a hashtable with an HTTP interface was called a "database". Of course as nod to the said filthy rich guys from the 20th century we called them "noSQL" "databases" so as to let them continue to charge money from all those silly people in the 20th century that built their information systems on (the now "defunct" :) "databases".
> All the in-memory stuff is nothing but a cache, distributed or not.
That's flat out wrong.
A cache is a limited store that maintains a sub-set of the data that has been placed in it. Typically the eviction policy is temporal.
A database or datastore on the other hand requires explicit removal of data that has been placed in it.
p.s. Which is why we can meaningfully talk about "cache misses" in context of a perfectly functional cache, but "missing" data in a database is generally discussed in context of a buggy datastore or database.
p.s.s. Most certainly we can have pure in-memory datastores/databases, as semantics of a database are orthogonal to its datastore component. And you don't have to take some random hn user's word for it. Go ahead and ask Michael Stonebraker. :)
Oh, come on. Old time RDBMS have been designed to survive a sudden power outage - the system would rollback all the partially committed transactions to recover to the consistent state of the database.
The durability and data consistency is what defines a database in the first place.
For cache vs. database metaphor - think of the difference between a RAM-disk and HDD. This is fundamental difference. Protocol details are irrelevant.
This is why, say, sqlite is a database, while redis is not.
Reducing technology assessment to puns is ultimately not very informative. I recommend you read up on Stonebraker's work the past few years. Durability issues of in-mem DBs are addressed.
It is certainly true that many pure mem vendors out there are playing fast and loose with terminology, but if one were to accept your assertions, then when the day arrives when spinning disks are antiques then I guess we no longer would have databases.
