  When multiple tenants compete for resources, database performance tends to
suffer. Yet there are scenarios where guaranteed sub-millisecond latencies are
crucial, such as in real-time data processing, IoT devices, or when operating
in safety-critical environments. In this paper, we study how to make query
latencies deterministic in the face of noise (whether caused by other tenants
or unrelated operating system tasks). We perform controlled experiments with an
in-memory database engine in a multi-tenant setting, where we successively
eradicate noisy interference from within the system software stack, to the
point where the engine runs close to bare-metal on the underlying hardware.
  We show that we can achieve query latencies comparable to the database engine
running as the sole tenant, but without noticeably impacting the workload of
competing tenants. We discuss these results in the context of ongoing efforts
to build custom operating systems for database workloads, and point out that
for certain use cases, the margin for improvement is rather narrow. In fact,
for scenarios like ours, existing operating systems might just be good enough,
provided that they are expertly configured. We then critically discuss these
findings in the light of a broader family of database systems (e.g., including
disk-based), and how to extend the approach of this paper accordingly.
