Chuzhe Tang | 唐楚哲

Today, the wide adoption of distributed service-oriented applications has rendered multi-database transactions increasingly important. They protect cross-service workflows that access multiple database systems from concurrency anomalies and failures. This paper presents Sonata, a new multi-database transaction system that provides high performance, global serializability, and seamless integration with existing applications and database systems. Sonata builds on the theory of commitment ordering to ensure global serializability and uses two-phase commit for atomicity and durability. Instead of treating database systems as black box storage, Sonata reuses existing database systems’ concurrency control yet refrains from exposing or modifying their internals. It performs additional non-blocking coordination only at prepare time via applicationlevel shim layers, allowing applications to incorporate Sonata without changing their existing queries or database systems. Evaluation using TPC-C shows that Sonata incurs 7.1% coordination overhead on average and outperforms prior work by up to 1114.3%.

Transactions are the fundamental database abstraction for ensuring application correctness under concurrency and failures. Using database transactions, developers are only tasked with demarcating critical business logic into transactions, and the underlying database system is responsible for coordinating their execution. Yet, in today’s Web applications, transactions are often constructed in an ad hoc manner. That is, developers might explicitly use locking primitives or manual validation to coordinate critical code fragments, instead of relying on database transactions. We refer to such application-coordinated transactions as ad hoc transactions.
This paper presents the first comprehensive study on ad hoc transactions. Examining 91 ad hoc transaction instances taken from eight popular open-source Web applications, we find that (i) every application studied uses ad hoc transactions (up to 16 per application), 71 of which play critical roles; (ii) compared with database transactions, coordination strategies of ad hoc transactions is much more flexible; (iii) ad hoc transactions are error-prone—53 of them have correctness issues, and 33 of them are confirmed by developers; and (iv) ad hoc transactions have the potential to improve performance in contentious workloads by utilizing application semantics such as access patterns. Finally, this paper concludes with a discussion about the implications of ad hoc transactions and opportunities for future research.

Many transactions in web applications are constructed ad hoc in the application code. For example, developers might explicitly use locking primitives or validation procedures to coordinate critical code fragments. We refer to database operations coordinated by application code as ad hoc transactions. Until now, little is known about them. This paper presents the first comprehensive study on ad hoc transactions. By studying 91 ad hoc transactions among 8 popular open-source web applications, we find that (i) every studied application uses ad hoc transactions (up to 16 per application), 71 of which play critical roles; (ii) compared with database transactions, concurrency control of ad hoc transactions is much more flexible; (iii) ad hoc transactions are error-prone—53 of them have correctness issues, and 33 of them are confirmed by developers; and (iv) ad hoc transactions have the potential to improve performance in contentious workloads by utilizing application semantics such as access patterns. Finally, implications of ad hoc transactions to the database research community are discussed.

Many transactions in web applications are constructed ad hoc in the application code. For example, developers might explicitly use locking primitives or validation procedures to coordinate critical code fragments. We refer to database operations coordinated by application code as ad hoc transactions. Until now, little is known about them. This paper presents the first comprehensive study on ad hoc transactions. By studying 91 ad hoc transactions among 8 popular open-source web applications, we find that (i) every studied application uses ad hoc transactions (up to 16 per application), 71 of which play critical roles; (ii) compared with database transactions, concurrency control of ad hoc transactions is much more flexible; (iii) ad hoc transactions are error-prone—53 of them have correctness issues, and 33 of them are confirmed by developers; and (iv) ad hoc transactions have the potential to improve performance in contentious workloads by utilizing application semantics such as access patterns. Based on the findings, we discuss the implications of ad hoc transactions to the database research community.

We present XIndex, a concurrent ordered index designed for fast queries. Similar to a recent proposal of the learned index, XIndex uses learned models to optimize index efficiency. Comparing with the learned index, XIndex is able to effectively handle concurrent writes without affecting the query performance by leveraging fine-grained synchronization and a new compaction scheme, Two-Phase Compaction. Furthermore, XIndex adapts its structure according to run-time workload characteristics to support dynamic workload. We demonstrate the advantages of XIndex with both YCSB and TPC-C (KV), a TPC-C variant for key-value stores. XIndex achieves up to 3.2× and 4.4× performance improvement comparing with Masstree and Wormhole, respectively, on a 24-core machine, and it is open-sourced.