Databases

How InnoDB uses transaction IDs, undo-based row versions, and Read Views so readers can observe consistent historical versions without blocking writers.

InnoDB write-ahead logging, redo buffering, fsync policy, group commit, crash recovery, and the relationship between redo log and binlog.

How undo records support transaction rollback and MVCC version reconstruction, and why long transactions delay undo purge.

InnoDB transaction boundaries, ACID mechanisms, isolation levels, consistent reads, locking reads, MVCC, redo, and undo.

Logical and physical storage of InnoDB pages across system, file-per-table, undo, and temporary tablespaces.

How InnoDB clustered indexes differ from MyISAM's separate data and index storage.

Transactional MySQL storage with clustered indexes, MVCC, redo/undo, locking, and buffer-pool caching.

Writing dirty buffer-pool pages and redo state to durable storage under checkpoints and background pressure.

PostgreSQL's relational engine, MVCC, WAL, extensibility, indexes, and operational model.

Read Committed, Repeatable Read, Serializable, snapshots, and serialization failures.