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conference & journal articles
2021
BullFrog: Online Schema Evolution via Lazy Evaluation
In Proceedings of SIGMOD,
2021
This paper presents BullFrog, a relational DBMS that supports single-step, non-backwards compatible schema migrations without downtime, and without advanced warning.
When a schema migration is presented, BullFrog initiates a logical switch to the new schema, but physically migrates affected data lazily, as it is demanded by incoming transactions. BullFrog’s internal concurrency control algorithms and data structures enable concurrent processing of schema migration operations with post-migration transactions, while ensuring exactly-once migration of all old data into the physical layout required by the new schema.
BullFrog is implemented as an open source extension to PostgreSQL. Experiments using this prototype over a TPC-C based workload (supplemented to include schema migrations) show that BullFrog can achieve zero-downtime migration to non-trivial new schemas with near-invisible impact on transaction throughput and latency.