An index invisible test that exposed an unindexed subquery

Before dropping what appeared to be an unused composite index on our transactions table, we followed the rule of making the index invisible first in our staging database.

-- Toggle visibility without dropping the data:
ALTER TABLE transactions ALTER INDEX idx_user_status INVISIBLE;

-- If performance degrades, re-enabling it is instant (no index rebuild):
ALTER TABLE transactions ALTER INDEX idx_user_status VISIBLE;

Within thirty minutes of making it invisible, an internal compliance audit export jumped from 800ms to 42 seconds. A subquery in the report relied on the index without matching the primary query planner path. Making the index invisible saved us from a disastrous production drop.