The Question of Ownership in a Sharing Economy

Abstrac

The Case For Heterogeneous HTAP

ABSTRACT Modern database engines balance the demanding requirements of mixed, hybrid transactional and analytical processing (HTAP) workloads by relying on i) global shared memory, ii) system-wide cache coherence, and iii) massive parallelism. Thus, database engines are typically deployed on multi-socket multi-cores, which have been the only platform to support all three aspects. Two recent trends, however, indicate that these hardware assumptions will be invalidated in the near future. First, hardware vendors have started exploring alternate non-cache-coherent shared-memory multi-core designs due to escalating complexity in maintaining coherence across hundreds of cores. Second, as GPGPUs overcome programmability, performance, and interfacing limitations, they are being increasingly adopted by emerging servers to expose heterogeneous parallelism. It is thus necessary to revisit database engine design because current engines can neither deal with the lack of cache coherence nor exploit heterogeneous parallelism. In this paper, we make the case for Heterogeneous-HTAP (H 2 TAP), a new architecture explicitly targeted at emerging hardware. H 2 TAP engines store data in shared memory to maximize data freshness, pair workloads with ideal processor types to exploit heterogeneity, and use message passing with explicit processor cache management to circumvent the lack of cache coherence. Using Caldera, a prototype H 2 TAP engine, we show that the H 2 TAP architecture can be realized in practice and can offer performance competitive with specialized OLTP and OLAP engines

Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba3ZnIr2O9

We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d(4)) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J = 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK