GBase 8a Performance Anomaly: One Parameter Change Caused 10 TB Disk Storm

A single parameter adjustment in GBase 8a, increasing group_concat_max_len, triggered a chain reaction that turned a 200,000-row sort into a 10 TB disk write storm. Queries that normally completed in seconds ran for over three hours, with one node's I/O pegged at 900 MB/s. The case study details how the change caused a cascade of performance degradation across the production cluster.