Redefining Cost Estimation in Database Systems: The Role of Execution Plan Features and Machine Learning

Accurate query runtime prediction is a critical component of effective query optimization in modern database systems. Traditional cost models, such as those used in PostgreSQL, rely on static heuristics that often fail to reflect actual query performance under complex and evolving workloads. This remains an active area of research, with recent work exploring machine learning techniques to replace or augment traditional cost estimators. In this paper, we present a machine learning-based framework for predicting SQL query runtimes using execution plan features extracted from PostgreSQL. Our approach integrates scalar and structural features from execution plans and semantic representations of SQL queries to train predictive models. We construct an automated pipeline for data collection and feature extraction using parameterized TPC-H queries, enabling systematic evaluation of multiple modeling techniques. Unlike prior efforts that focus either on cardinality estimation or on synthetic cost metrics, we model the actual runtimes using fine-grained plan statistics and query embeddings derived from execution traces, to improve the model accuracy. We compare baseline regressors, a refined XGBoost model, and a sequential LSTM-based model to assess their effectiveness in runtime prediction. Our dataset includes over 1000 queries generated from TPC-H query templates executed in PostgreSQL with EXPLAIN ANALYZE. Experimental results show that the XGBoost model significantly outperforms others, achieving a mean squared error of 0.3002 and prediction accuracy within 10% of the true runtime in over 65% of cases. The findings highlight the potential of tree-based learning combined with execution plan features for improving cost estimation in query optimizers.