Learned cardinality estimation methods have achieved high precision compared
to traditional methods. Among learned methods, query-driven approaches face the
data and workload drift problem for a long time. Although both query-driven and
hybrid methods are proposed to avoid this problem, even the state-of-the-art of
them suffer from high training and estimation costs, limited scalability,
instability, and long-tailed distribution problem on high cardinality and
high-dimensional tables, which seriously affects the practical application of
learned cardinality estimators. In this paper, we prove that most of these
problems are directly caused by the widely used progressive sampling. We solve
this problem by introducing predicates information into the autoregressive
model and propose Duet, a stable, efficient, and scalable hybrid method to
estimate cardinality directly without sampling or any non-differentiable
process, which can not only reduces the inference complexity from O(n) to O(1)
compared to Naru and UAE but also achieve higher accuracy on high cardinality
and high-dimensional tables. Experimental results show that Duet can achieve
all the design goals above and be much more practical and even has a lower
inference cost on CPU than that of most learned methods on GPU