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PSL-DB: Non-Volatile Memory-optimized LSM-Tree with Skip List
Chanyeol Park, Dongui Kim, Beomseok Nam
http://doi.org/10.5626/JOK.2020.47.7.635
With the release of Intel"s Optane DC Persistent Memory, non-volatile memory, offering higher capacity than DRAM and showing higher performance than SSD and HDD, is in the spotlight as the next generation of storage devices. In this paper, we propose the Persistent Skip List DataBase (PSL-DB), a key-value store system optimized for the Optane DCPM in app-direct mode. PSL-DB uses a byte-addressable skip list that significantly reduces the I/O traffic as it avoids redundant writes. PSL-DB also does not sacrifice write performance for read performance as it does not degrade the write performance via artificial governors. In our experiments using Intel Optane DC Persistent Memory, PSL-DB shows significantly higher query processing throughput than legacy LevelDB that stores SSTables in Optane DC PM.
A Persistent Log Buffer Technique using Non-volatile Memory for In-Memory Key-Value Databases
Doyoung Kim, Won Gi Choi, Hanseung Sung, Jihwan Lee, Sanghyun Park
http://doi.org/10.5626/JOK.2018.45.11.1193
Redis, an In-Memory Key-Value Database, is widely used in services that require real time data processing and storage. Since main memory is volatile, Redis has a problem of data loss if the system is terminated abnormally. To prevent this problem, Redis stores logs on disk, preventing data loss by restoring logs when the system is terminated. The AOF recovery mechanism, a method of appending requested commands in disk as a log format, operates with the “everysec” policy that writes logs every second, and the “always” policy that writes a log every time a command is requested. The “everysec” policy does not degrade performance of Redis, but data loss can occur if the system is terminated abnormally within one second. Conversely, the “always” policy does not cause data loss, but it requires disk operation for every command, causing performance degradation. We propose a system model that constructs AOF buffer in non-volatile memory and stores logs in the buffer, which are not synchronized to disk in the “everysec” policy. The proposed model prevents data loss and has approximately 100 times better performance than the “always” policy.
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