column-renames-metadata-onlylisted

# Column Renames (Metadata-Only) ## What PostgreSQL's `ALTER TABLE RENAME COLUMN` is a **metadata-only** operation. It changes the column name in the system catalogs (`pg_attribute`) without touching the actual table data. It's instant regardless of table size. ## Why This matters because renaming a column on a 100-million-row table takes the same time as renaming one on a 10-row table: effectively zero. No table rewrite, no data movement, no downtime. ## How ```sql ALTER TABLE public."Applicant" RENAME COLUMN "SpeialtyRequirement" TO "SpecialtyRequirement"; ``` What happens internally: 1. PostgreSQL acquires an `ACCESS EXCLUSIVE` lock on the table (very briefly) -- this is the strictest lock mode but the hold time is sub-millisecond since only catalog metadata is updated (PG 16 docs: sql-altertable.html) 2. Updates `pg_attribute.attname` for that column's OID 3. Releases the lock Total time: typically < 1ms. ## What It Does NOT Do - Does NOT update stored procedures that reference the old column name - Does NOT update views that reference the old column name - Does NOT update application code - Does NOT update indexes (indexes reference column attnum, not name) - Does NOT change parameter names in function signatures This is why had to separately update 4 stored procedures -- the column rename alone would have left them broken with `"column does not exist"` errors. ## When to Use - Fixing typos in column names - Standardizing naming conventions - Any