Answer
Tuple freezing marks old tuples with special XIDs to prevent wraparound. Autovacuum freezes tuples in stages to avoid large rewrites and ensure data remains valid indefinitely.
Quick Answer
Tuple freezing replaces the real transaction ID in old tuples with FrozenXID (a special value that's always considered "in the past"). This is required because XID is 32-bit and wraps around after ~2 billion transactions. Frozen tuples are visible to all transactions regardless of XID comparison. Autovacuum freezes tuples when they're old enough (vacuum_freeze_min_age). Without freezing, XID wraparound causes data to become invisible.
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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