Prashant Kumar Pathak

Prashant Kumar Pathak, Chandra Biksheswaran Mouleeswaran, Rama Teja Repaka

Large-scale cloud security platforms must continuously query millions of structured cloud resource records distributed across thousands of tenant accounts. Broad, account-spanning queries saturate database infrastructure, producing P95 latencies exceeding 60 seconds. We identify buffer cache pressure as the dominant latency driver: in a controlled experiment, the same query executing with the same plan completed in 3.7 seconds when its working set was memory-resident and 94 seconds when concurrent load had evicted those pages. No query plan optimization can address this; the only effective intervention is reducing the number of pages each query must touch. We present the Heuristic Search Space Partitioning System (HSSPS), a query-time optimization layer that logically partitions the search space through dynamic predicate injection, without schema modification. A two-phase heuristic engine selects partition key values and scores candidate query plans before execution. A client-side page token maintains cross-partition traversal state without server-side sessions, enabling horizontal scalability. Controlled evaluation across representative query types demonstrates 50-97% P95 latency reduction (95-97% on high-cardinality queries), 8-10x throughput improvement, and 41x reduction in average active sessions. Production rollout across live multi-tenant traffic reduced P95 latency from 61s to 2s across successive releases, sustained over 14,000 eligible queries per measurement window. The technique generalizes to any multi-tenant system where broad queries execute against large shared databases and physical schema modification is impractical.

Prashant Kumar Pathak, Tarun Kumar Sharma

Vector hubness, where a few points become nearest neighbors of many queries, creates a poisoning risk in retrieval-augmented generation (RAG): one injected document can influence unrelated requests. Existing defenses use periodic reverse-kNN scans, leaving an exposure window and repeated corpus-wide work. We study admission-time control, scoring each candidate against sentinel queries and quarantining hub-like documents before insertion. Across two 100,000-document corpora, five encoders, and disjoint attacker and defender query sets, a global gate achieves recall 1.0 at the decisive embedding-space point (>=0.92 across the effective range) and 0.91 +/- 0.07 on HotFlip attacks, with 1% false positives on general documents. A per-topic gate provides no reliable benefit, consistent with anisotropy coupling local and global visibility. Thresholds are maintained incrementally, with corpus-size-independent insertion cost and amortized deletion cost. On HNSW, admission adds about 3.1% to ingestion latency, scoring remains flat to 10^6 vectors, and 1.2% of decisions flip under approximate indexing, none involving attacks. Provenance complements the gate for natural or tight-domain hubs.

Prashant Kumar Pathak

Cloud data warehouses bill compute based on slot-time consumed. In shared multi-tenant environments, query cost is highly variable and hard to estimate before execution, causing budget overruns and degraded scheduling. Static query-planner heuristics fail to capture complex SQL structure, data skew, and workload contention. We present a feature-scoped machine learning approach that predicts BigQuery slot-time before execution using only pre-execution observable signals: a structured query complexity score derived from SQL operator costs, data volume features from planner estimates and workload metadata, and textual features from query text. We deliberately exclude runtime factors (slot-pool utilization, cache state, realized skew) unknowable at submission. The model uses a HistGradientBoostingRegressor trained on log-transformed slot-time, with a TF-IDF + TruncatedSVD-512 text pipeline fused with numeric and categorical features. Trained on 749 queries across seven deployment environments and evaluated out-of-distribution on 746 queries from two held-out environments, the model achieves MAE 1.17 slot-minutes, RMSE 4.71, and 74% explained variance on the full workload. On cost-significant queries (slot-time >= 0.01 min, N=282) the model achieves MAE 3.10 versus 4.95 for a predict-mean baseline and 4.54 for predict-median, a 30-37% reduction. On long-tail queries (>= 20 min, N=22) the model does not outperform trivial baselines, consistent with the hypothesis that long-tail queries are dominated by unobserved runtime factors outside the current feature scope. A complexity-routed dual-model architecture is described as a practical refinement, and directions for closing the long-tail gap are identified as future work.