Transactions

Database 02 Sep 2026 5 min read

Understanding Write Skew and Transaction Isolation

Transaction isolation is often explained with dirty reads and lost updates, but another anomaly is especially important for multi-row business rules: write skew. Write skew occurs when concurrent transactions read the same valid state, make decisions independently, and update different rows in a way that produces an invalid combined state. Because they do not overwrite the same row, ordinary write-conflict detection may not stop them. A simple invariant Imagine an on-call table where at least one doctor must remain available:

Database Transactions

Database 02 Sep 2026 8 min read

SQLite Savepoints: Partial Rollback Inside a Transaction

A transaction normally gives application code an all-or-nothing boundary: either commit its changes or roll them all back. Some workflows need a smaller recovery point inside that larger unit of work. SQLite provides that recovery point with savepoints. A savepoint lets code mark a position inside a transaction, perform additional work, and later undo only the changes made after that position. The surrounding transaction can remain active. Savepoints are useful for batch processing, optional sub-operations, library code that may run inside an existing transaction, and workflows where one recoverable step should not discard earlier valid work.

Database SQLite

Database 01 Sep 2026 5 min read

Transaction Isolation and Safe Database Retries

Database transactions make groups of reads and writes atomic, but atomicity alone does not answer what concurrent transactions are allowed to observe. That is the job of isolation. The practical challenge appears when correct transactions conflict. Strong isolation can intentionally abort one transaction rather than allow an invalid interleaving. Applications need to distinguish those retryable concurrency failures from ordinary errors. Isolation protects invariants, not just statements Consider two concurrent requests that reserve the last available item.

Database Transactions