Tag: MVCC

All the articles with the tag "MVCC".

• MySQL InnoDB Isolation Levels — Measuring phantom reads across all 4 levels and decomposing why InnoDB RR is stronger than the ANSI standard

  3 May, 2026

  The ANSI SQL standard does not guarantee that REPEATABLE READ blocks phantom reads. Yet MySQL InnoDB's RR does. I nailed down this commonly-cited claim with direct measurements — RU/RC: phantom occurs (A1=0 → INSERT → A2=1), RR: blocked (A2=0), SERIALIZABLE: INSERT itself waits 1.56s. Then I decomposed why MySQL RR is stronger than the ANSI standard via three mechanisms — consistent read snapshot, gap lock, and MVCC undo log — to nail down with measurements that for payment domains, RR alone is sufficient.