The AWS Lambda 'Kiss of Death'

A Galera writer node froze after InnoDB undo history ballooned. Pooled AWS Lambda connections left transactions open and pinned MVCC read views. The team killed stalled sessions, enabled innodb_undo_log_truncate, and capped innodb_max_undo_log_size. They also set session transaction_isolation=READ-COMMITTED. That shrinks MVCC read views and speeds purge.