“Tape is Dead, Disk is Tape, Flash is Disk, RAM Locality is King.”Jim Gray · Tape is Dead, Disk is Tape, Flash is Disk, RAM Locality is King · 2006 · Prezentare la Storage Guru Gong Show, Redmond, 10 decembrie 2006 (reluată la CIDR 2007)
Every rung down costs a factor of a hundred, and spilling onto it raises no error.
Gray's figures still hold as orders of magnitude: RAM in nanoseconds, SSD in tens of microseconds, spinning disk in milliseconds, object storage in tens of milliseconds plus a per-request cost. Between rungs are factors of a hundred. "Disk is tape" means disk is only worth it for sequential reads — hence the columnar format, compression and sorted layout from lesson 25: they turn random access into a scan. "RAM locality is king" means the fast query is the one whose working set fits in memory: the join's hash table, the sort, the aggregation. The moment it no longer fits, it spills to the next rung and slows down ten to a hundred times, without raising any error. Cloud warehouses make the hierarchy explicit: object storage is the base, cheap and unlimited; compute nodes keep a cache on local SSD; recent results sit in a result cache. Sizing is not "how much memory the server has" but "how much memory each query slot gets" — ten parallel queries share the same RAM. Columnar compression is, in Gray's terms, the cheapest way to climb a rung: the same data, five times smaller, fits where it did not fit before.
Why it matters A query that "worked yesterday" and today takes ten times longer did not get harder; its working set dropped a rung in the hierarchy.