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Your Query Plan Flipped. Your p99 Fell Off a Cliff.

You did not change the query. You did not change the code. The orders table crossed twelve million rows, the planner decided a full scan was cheaper than the index, and p99 went from forty milliseconds to two point four seconds overnight.

This Short draws the flip moving: the Go service issues the same query it always did, the planner picks Seq Scan, the scan reads the entire table to return twenty rows, and EXPLAIN ANALYZE prints the whole story in its first line. Then the fix: CREATE INDEX CO