tl;dr:Andrei delves into QuestDB’s unique hash table, FastMap, designed to enhance SQL execution for JOIN and GROUP BY operations. FastMap employs open addressing and linear probing, optimized for high performance in database environments. It supports variable-size keys and fixed-size values, facilitating efficient data handling and updates. Notably, FastMap operates off-heap, reducing garbage collection pressure to improve performance.
tl;dr:The team at QuestDB faced challenges with segfaults, data corruption, and concurrency bugs. To address these, the team implemented fuzz testing, an automated software testing technique that provides invalid or unexpected data to a program to monitor for exceptions. This article details the process of introducing fuzz testing, revealing critical issues and leading to more robust database performance. The team also collaborated with SQLancer, a tool for testing SQL Database Management Systems, to uncover issues in their SQL engine.