advanced~3h
MySQL vs PostgreSQL — Storage Engine & MVCC Architecture Compared
A direct architectural comparison between InnoDB's clustered-index, undo-log MVCC model and PostgreSQL's heap-table, tuple-versioning MVCC model — and why that one structural difference explains most of the operational behavior that surprises people moving between the two engines.
Learning objectives
- Explain how InnoDB's clustered primary-key index physically organizes a table, and how that differs from PostgreSQL's heap storage with a separate, non-clustered primary-key index.
- Describe how InnoDB implements MVCC using undo logs versus PostgreSQL's row-versioning with xmin/xmax tuple headers, and what each approach costs on an UPDATE.
- Explain why PostgreSQL needs VACUUM to reclaim dead tuples while InnoDB's undo-log model doesn't accumulate table bloat the same way.
- Describe what happens to each engine under a long-running transaction, and why that failure mode looks different in MySQL/InnoDB versus PostgreSQL.
- Make a reasoned, trade-off-aware choice between MySQL and PostgreSQL for a new project based on workload shape rather than familiarity alone.
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MySQL vs PostgreSQL — Storage Engine & MVCC Architecture Compared