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The physical world evolves. The cyber world evolves and grows with big data, with social media as a major component of information growth. Classic ML models are limited by their static training data with implicit Complete and Timeless Knowledge assumptions. In an evolving world, static training data suffer from knowledge obsolescence due to truly novel timely information. Knowledge obsolescence introduces a widening distance between static ML models and the evolving world, called cyber-physical gap. Periodic retraining of new models may restore their accuracy temporarily, but subsequently their performance will deteriorate with widening cyber-physical gap. Knowledge obsolescence affects statically trained models of any size, including LLMs. Two major research challenges arise from cyber-physical gap: (1) collection and incorporation of space-time aware ground truth training data, and (2) understanding and capturing of the varying speed of information and knowledge evolution when the physical and cyber worlds evolve. 

Machine learning models with explainable predictions are increasingly sought after, especially for real-world, mission-critical applications that require bias detection and risk mitigation. Inherent interpretability, where a model is designed from the ground-up for interpretability, provides intuitive insights and transparent explanations on model prediction and performance. In this paper, we present COLABEL, an approach to build interpretable models with explanations rooted in the ground truth. We demonstrate COLABEL in a vehicle feature extraction application in the context of vehicle make-model recognition (VMMR). By construction, COLABEL performs VMMR with a composite of interpretable features such as vehicle color, type, and make, all based on interpretable annotations of the ground truth labels. First, COLABEL performs corroborative integration to join multiple datasets that each have a subset of desired annotations of color, type, and make. Then, COLABEL uses decomposable branches to extract complementary features corresponding to desired annotations. Finally, COLABEL fuses them together for final predictions. During feature fusion, COLABEL harmonizes complementary branches so that VMMR features are compatible with each other and can be projected to the same semantic space for classification. With inherent interpretability, COLABEL achieves superior performance to the state-of-the-art black-box models, with accuracy of 0.98, 0.95, and 0.94 on CompCars, Cars196, and BoxCars116K, respectively. COLABEL provides intuitive explanations due to constructive interpretability, and subsequently achieves high accuracy and usability in mission-critical situations. 

Mission-critical, real-time, continuous stream processing applications that interact with the real world have stringent latency requirements. For example, e-commerce websites like Amazon improve their marketing strategy by performing real-time advertising based on customers' behavior, and latency long tail can cause significant revenue loss. Recent work [39] showed a positive correlation between latency long tail and variance in the execution time of synchronous invocation chains (critical paths) in microservices benchmarks. This paper shows that asynchronous, very short but intense resource demands (called millibottlenecks) outside of critical paths can also cause significant latency long tail. Using a traffic analysis stream processing application benchmark, we evaluated the impact of asynchronous workload bursts generated by a multi-layer data structure called LSM-tree (log-structured merge-tree) for continuous checkpointing. Outside of the critical path, LSM-tree relies on maintenance operations (e.g., flushing/compaction during a checkpoint) to reorganize LSM-tree in memory and on disk to keep data access latency short. Although asynchronous, such recurrent maintenance operations can cause frequent millibottlenecks, particularly when they overlap, a problem we call ShadowSync. For scheduling and statistical reasons, significant latency long tail can arise from ShadowSync caused by asynchronous recurrent operations. Our experimental results show that with typical settings of benchmark components such as RocksDB, ShadowSync can prolong request message latency by up to 2 seconds. We show effective mitigation methods can alleviate both scheduled and statistical ShadowSync reducing the latency long tail to less than 20% of the original at the 99.9th percentile. 

A rapidly evolving situation such as the COVID-19 pandemic is a significant challenge for AI/ML models because of its unpredictability. The most reliable indicator of the pandemic spreading has been the number of test positive cases. However, the tests are both incomplete (due to untested asymptomatic cases) and late (due the lag from the initial contact event, worsening symptoms, and test results). Social media can complement physical test data due to faster and higher coverage, but they present a different challenge: significant amounts of noise, misinformation and disinformation. We believe that social media can become good indicators of pandemic, provided two conditions are met. The first (True Novelty) is the capture of new, previously unknown, information from unpredictably evolving situations. The second (Fact vs. Fiction) is the distinction of verifiable facts from misinformation and disinformation. Social media information that satisfy those two conditions are called live knowledge. We apply evidence-based knowledge acquisition (EBKA) approach to collect, filter, and update live knowledge through the integration of social media sources with authoritative sources. Although limited in quantity, the reliable training data from authoritative sources enable the filtering of misinformation as well as capturing truly new information. We describe the EDNA/LITMUS tools that implement EBKA, integrating social media such as Twitter and Facebook with authoritative sources such as WHO and CDC, creating and updating live knowledge on the COVID-19 pandemic. 

The broad adoption of fanout queries on distributed datastores has made asynchronous event-driven datastore drivers a natural choice due to reduced multithreading overhead. However, through extensive experiments using the latest datastore drivers (e.g., MongoDB, HBase, DynamoDB) and YCSB benchmark, we show that an asynchronous datastore driver can cause unexpected performance degradation, especially in fanout-query scenarios. For example, the default MongoDB asynchronous driver adopts the latest Java asynchronous I/O library, which uses a hidden on-demand JVM level thread pool to process fanout query responses, causing a surprising multithreading overhead when the query response size is large. A second instance is the traditional wisdom of modular design of an application server and the embedded asynchronous datastore driver can cause an imbalanced workload between the two components due to lack of coordination, incurring frequent unnecessary system calls. To address the revealed problems, we introduce DoubleFaceAD--a new asynchronous datastore driver architecture that integrates the management of both upstream and downstream workload traffic through a few shared reactor threads, with fanout-query-aware priority-based scheduling to reduce the overall query waiting time. Our experimental results on two representative application scenarios (YCSB and DBLP) show DoubleFaceAD outperforms all other types of datastore drivers up to 34% on throughput and 1.9\texttimes{} faster on 99th percentile response time.