What Attributes Makes It an In-Memory DBMS?
Although I've been doing quite a bit of reading, I'm still trying to get my head around just what makes something an In-Memory DBMS. One of my touch stones for comparing what appears to be a relatively new notion is the relatively older IBM i operating system (a.k.a., AS/400, S/38) with its integrated DBMS. Within this OS, every byte of the DB resides persistently within the system's address space from the moment the byte of created. Although IBM i does support a notion of Process-local addressing, there need not be any notion of mapping of DB files into an address space since the tables and indexes (and what have you) already have an address that any process/thread can use during its access. Now couple that with a large amount of DRAM - I understand now approaching or above the terabyte range - the DRAM then acts as a cache for the DB objects residing persistently on HDD/SDD. Given all of that, picture a DRAM large enough to hold the active DB objects and all other control structures. So does this constitute an "In-Memory DBMS"?