A mechanism that shows readers a different version of data being updated, to reduce contention.
Short for Multi-Version Concurrency Control. A concurrency-control scheme that keeps multiple versions of a row to reduce contention between reads and writes. It's the standard concurrency-control mechanism in most major RDBMSes, including PostgreSQL and MySQL's InnoDB -- because reads don't block writes and writes don't block reads, it dramatically cuts down on lock waits.
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