Answer
InnoDB uses undo logs to store old row versions. Each transaction reads based on its snapshot ID, enabling non-blocking reads while writers modify the latest row version.
Quick Answer
InnoDB MVCC internals: each row has DB_TRX_ID (last modifying transaction) and DB_ROLL_PTR (undo log chain pointer). At transaction start, MySQL creates a read view capturing which transaction IDs are active. For each row, if DB_TRX_ID is visible in the read view, use this row version. Otherwise, follow DB_ROLL_PTR to the undo log to find the last visible version. Readers never block writers.
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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