Persistent Transactional Memory for Databases

Hardware transactional memory (HTM) and byte-addressable nonvolatile memory (NVM) are already available in new computer equipment. It is tempting, but not trivial, to combine them to implement transactions having the capabilities of ACID (atomicity, consistency, isolation and durability), by using HTM for consistency and isolation, and NVM for durability. ACID transactions are especially useful in databases but, because of the size of database transactions, the challenge is to cope with the inherent HTM limitations of size and contention level. In this paper, we first present persistent HTM (PHTM), a software-hardware solution for ACID transactions with HTM. We continue with two methods to mitigate PHTM limitations. One is a persistent hybrid TM algorithm called PHyTM, which allows PHTM transactions to execute concurrently with pure software, unbounded transactions. The other is for workloads where most transactions are too large for PHTM. For the purpose we propose a new algorithm called split transactions execution (STE), which is tailored for relational database transactions. In a nutshell, this paper discusses the extension of HTM to ACID database transactions on NVM.