Migrating user data can be a challenging task due to its potential impact on human users. There are three main approaches to migrating user accounts: the big bang migration, where all users are migrated at once; segment by segment migration, where smaller chunks of users are migrated one at a time; and slow migration, where each user is migrated individually as they log in. Each approach has its strengths and weaknesses, including factors such as risk, timeline, implementation complexity, and potential impact on user experience. The big bang migration offers simplicity and speed but also carries higher risks due to the large number of users affected. Segment by segment migration decreases cutover risk but introduces additional complexities and planning requirements. Slow migration limits the blast radius in case of issues during the migration, allows for more control over password management, and simplifies application cutover. However, it requires running both systems for a longer period and may involve additional technical considerations. Ultimately, the choice of approach depends on factors such as the size of the user base, the complexity of the system, and the desired level of risk tolerance.