Answer
Dead tuples are obsolete row versions created by updates and deletes. They accumulate because PostgreSQL never overwrites rows.
Quick Answer
Dead tuples are old row versions left behind by UPDATE and DELETE operations in MVCC. When you update a row, PostgreSQL creates a new tuple version but keeps the old one visible for concurrent transactions. Once no active transaction needs the old version, it becomes a "dead tuple". Dead tuples accumulate, bloating tables and slowing queries. VACUUM removes dead tuples and marks space reusable.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ