How to truncate a table?

0-2 years experience

1. 1We have a local test database with a 'temp_user_sessions' table that gets bloated during integration tests. You need to clear all the data out of it quickly before each test run so the auto-increment IDs start back at 1. How would you write this script, and why wouldn't you just use a standard 'DELETE FROM' query?
2. 2You run a script to empty a 'logs' table using TRUNCATE, but MySQL throws an error saying it cannot be truncated because of a foreign key constraint, even though the referencing table is completely empty. What's going on here, and how would you safely resolve this to empty the table?

2-5 years experience

1. 1A developer ran a script that truncated a 'shopping_cart' table in our staging environment, expecting to be able to roll it back because they wrapped it in a 'START TRANSACTION' block. However, the data was permanently lost. Why did the transaction fail to protect the data, and how does MySQL handle transactions differently for DELETE versus TRUNCATE?
2. 2We are building a nightly cleanup job for a high-throughput 'audit_trail' table. The product requirement is that we must clear out all records older than 30 days, but we also have a downstream service that relies on a 'BEFORE DELETE' trigger on this table to sync data to an archive. If we decide to use TRUNCATE to wipe the table periodically instead of batch deletes, what happens to our sync service, and how would you design around this?

5-8 years experience

1. 1We have a 500GB 'analytics_events' table on a production MySQL instance with a 128GB InnoDB buffer pool. A junior engineer runs 'TRUNCATE TABLE analytics_events' during peak hours to clear out old test data. Suddenly, the entire database stalls, and API response times spike across the whole system. What is happening under the hood in InnoDB during a truncate of a massive table, and how would you safely drop or clear this data without causing a production outage?
2. 2We are designing a multi-tenant SaaS platform where each tenant's raw ingestion data is stored in its own table. When a tenant churns, we need to instantly purge their data. If we use TRUNCATE or DROP TABLE on these tables, we risk blocking the disk I/O of other active tenants on the same DB instance due to the OS-level file deletion overhead. How would you architect the data purging mechanism to avoid this I/O bottleneck?

8+ years experience

1. 1We are migrating a legacy monolithic MySQL database to a microservices architecture. We have a massive, highly-active 'orders' table that we need to deprecate and completely empty once the new service is live, but we cannot afford any lock escalation or replication lag on our read replicas during the decommissioning phase. How would you design the operational runbook for purging this data safely across a globally distributed replica set?
2. 2Our compliance team requires us to guarantee that when a user requests account deletion, their associated activity logs are physically purged from disk within 24 hours, not just logically marked as deleted. Given how InnoDB manages tablespaces and OS-level file allocation, how would you design our storage engine configuration and table schema strategy to ensure we can prove physical deletion to auditors without destroying DB performance?