Distributed databases have been widely researched and developed in recent years due to their scalability, availability, and consistency guarantees. The write-ahead logging (WAL) system is one of the most vital components in a database. It is still a non-trivial problem to design a replicated logging system as the foundation of a distributed database with the power of ACID transactions. This paper proposes PALF, a Paxos-backed Append-only Log File System, to address these challenges. The basic idea behind PALF is to co-design the logging system with the entire database for supporting database-specific functions and to abstract the functions as PALF primitives to power other distributed systems. Many database functions, including transaction processing, database restore, and physical standby databases, have been built based on PALF primitives. Evaluation shows that PALF greatly outperforms well-known implementations of consensus protocols and is fully competent for distributed database workloads. PALF has been deployed as a component of the OceanBase 4.0 database and has been made open-source along with it.

Security services for workflow systems are becoming increasingly important for cross-domain interoperability in insecure environments. Workflow interfaces and system components involve the whole spectrum of security services including authentication, authorization, access control, data confidentiality and integrity, audit, non-repudiation, and administration. With the equipment of these services, workflow systems can be used in a broader range of enterprise applications. In this paper, we address many security issues in typical workflow systems and present a security model that utilizes the secure socket layer protocol and HTTPS tunneling mechanism. This model provides flexible security facilities that are suitable for application-to-application operations and data exchange over the Internet.