Storage & Databases also: Multi-Version Concurrency Control

MVCC

Each row keeps versions; readers don't block writers.

In plain terms

Postgres, MySQL InnoDB, Oracle, CockroachDB. Vacuum/cleanup reclaims old versions.

Origin

Phil Bernstein and Nathan Goodman, "Concurrency Control in Distributed Database Systems," 1981, formalised MVCC in the database literature. Production roots: InterBase (1985), then Oracle, then Postgres (which got proper MVCC in 2000).

Where it shows up in production

PostgreSQL Every row carries xmin/xmax; readers see a snapshot. Vacuum is the GC for old versions.
MySQL InnoDB Undo log + row versioning; old versions kept in the undo segment, not the table.
CockroachDB & Spanner Distributed MVCC with HLC (hybrid logical clock) timestamps as version IDs.

Sources & further reading

Paper Bernstein & Goodman — Concurrency Control in Distributed Database Systems (1981)
Docs PostgreSQL — MVCC docs
Talk Bruce Momjian — MVCC Unmasked (talk)

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