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Multiversion Concurrency Control

The basic idea

  • T2 read A after T1 wrote a new version. (Compare to S2PL.)

  • T1 wrote B after T2 read the old version. (Compare to S2PL.)

Versions become obsolete

After T1 commits, transactions reading A and B see A2 and B2.

The old versions, A1 and B1 are obsolete once their readers complete (T2, T3).

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