The 5 PostgreSQL Migration Mistakes That Cause Production Outages

Most PostgreSQL migration outages are caused by the same five patterns. Each one involves a lock that blocks queries longer than expected, a table rewrite that no one anticipated, or a cascade effect that turns a simple schema change into minutes of downtime. Here are the five mistakes, the production incidents they cause, and the safe patterns to avoid them. Mistake #1: CREATE INDEX Without CONCURRENTLY The dangerous migration -- This looks harmless CREATE INDEX idx_orders_customer_id ON orders (customer_id); What happens in production A regular CREATE INDEX acquires a SHARE lock on the table. This lock blocks all INSERT, UPDATE, and DELETE operations for the entire duration of the index build. On a table with 1 million rows, an index build might take 5-30 seconds. On a table with 100 million rows, it can take minutes. During that entire time, every write to the table is blocked. Every API request that tries to insert or update a row in that table will queue up, waiting. The cascading