Answer
Hint bits mark tuples as committed or rolled back after checks, reducing future visibility lookups. These updates happen lazily and do not require WAL writes.
Quick Answer
Hint bits are two bits stored in each tuple header that cache the commit status of xmin and xmax. Initially unset, they are set the first time a query inspects the tuple and checks pg_clog (now pg_xact) for commit status. Once set (COMMITTED or ABORTED), future visibility checks skip the pg_clog lookup. Reduces overhead of repeated visibility checks for the same tuple.
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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