Consistent checkpointing is a critical for in-memory databases (IMDBs) but its resource-intensive nature poses challenges for small- and medium-sized deployments in cloud environments, where memory utilization directly affects operational costs. Although traditional fork-based checkpointing offers merits in terms of performance and implementation simplicity, it incurs a considerable rise in memory footprint during checkpointing, particularly under update-intensive workloads. Memory provisioning emerges as a practical remedy to handle peak demands without compromising performance, albeit with potential concerns related to memory over-provisioning.In this article, we propose MDC+, a memory-efficient fork-based checkpointing scheme designed to maintain a reasonable memory footprint during checkpointing by leveraging collaboration among an IMDB, a user-level memory allocator, and the operating system. We explore two key techniques within the checkpointing scheme: (1) memory dump-based checkpointing, which enables early memory release, and (2) hint-based segregated memory allocation, which isolates immutable and updatable data to minimize page duplication. Our evaluation demonstrates that MDC+ significantly lowers peak memory footprint during checkpointing without affecting throughput or checkpointing time.

In cloud computing, I/O-intensive workloads can be co-located with other applications or virtual machines on a single physical machine. In this case, copy-based I/O (buffered I/O) can lead to severe performance interference to other memoryintensive workloads. It is because that the buffered I/O consumes memory bandwidth during memory copy even though it benefits from caching. To address this problem, many zero-copy I/O schemes have been proposed but none of them provides both 1) transparent copy avoidance through read/write system calls and 2) benefits of kernel-level caching at the same time. To this end, this paper presents z-READ, an efficient and transparent zero-copy read I/O scheme based on page remapping and copy-on-write techniques. In our scheme, we introduce several optimizations that minimize the overheads of page remapping by reducing the number of remote TLB shootdown.We implement z- READ prototype in memory management of Linux kernel 4.12.9. Our experimental results show that the performance of the colocated memory-intensive workloads can be negatively affected by I/O-intensive workloads in the case of copy-based I/O (up to 1.96x slowdown in-memory configurations) while z-READ incurs only up to 1.07x slowdown for the respective configuration.

A large number of cloud datastores have been developed to handle the cloud OLTP workload. Double caching problem where the same data resides both at the user buffer and the kernel buffer has been identified as one of the problems and has been largely solved by using direct I/O mode to bypass the kernel buffer. However, maintaining the caching layer only in user-level has the disadvantage that the user process may monopolize memory resources and that it is difficult to fully utilize the system memory due to the risks of the forced termination of the process or the unpredictable performance degradation in case of memory pressure. In this paper, we propose a new I/O mode, DBIO, to efficiently exploit OS kernel buffer as a victim cache for user-level file content cache, enjoying the strengths of kernel-level cache rather than just skipping it. DBIO provides the new file read/write function calls, which enable user programs to dynamically choose the right I/O behavior based on their context when issuing I/Os instead of when opening the file. On the cloud key-value store workloads and the traditional OLTP workloads with the modified version of MySQL/InnoDB, DBIO improves the in-memory cache hit ratio and the transaction performance compared to both buffered and direct I/O mode, fully utilizing the user buffer and the kernel buffer without double caching.

Backup and recovery is an important feature of database systems since it protects data against unexpected hardware and software failures. Database systems can provide data safety and reliability by creating a backup and restoring the backup from a failure. Database administrators can use backup/recovery tools that are provided with database systems or backup/recovery methods with operating systems. However, the existing tools perform time-consuming jobs and the existing methods may negatively affect run-time performance during normal operation even though high-performance SSDs are used. In this paper, we present an SSD-assisted backup/recovery scheme for database systems. In our scheme, we extend the out-of-place update characteristics of flash-based SSDs for backup/recovery operations. To this end, we exploit the resources (e.g., flash translation layer and DRAM cache with supercapacitors) inside SSDs, and we call our SSD with new backup/recovery features BR-SSD. We design and implement the backup/recovery functionality in the Samsung enterprise-class SSD (i.e., SM843Tn) for more realistic systems. Furthermore, we conduct a case study of BR-SSDs in replicated database systems and modify MySQL with replication to integrate BR-SSDs. The experimental result demonstrates that our scheme provides fast recovery while it does not negatively affect the run-time performance during normal operation.