TY  - JOUR
T1  - Garbage Collection Synchronization Technique for Improving Tail Latency of Cloud Databases
AU  - Han, Seungwook 
AU  - Hahn, Sangwook Shane 
AU  - Kim, Jihong 
JO  - Journal of KIISE, JOK
PY  - 2017
DA  - 2017/1/14
DO  - 10.5626/JOK.2017.44.8.767
KW  - tail latency
KW  - cloud database
KW  - Cassandra
KW  - garbage collection
KW  - flash memory
AB  - In a distributed system environment, such as a cloud database, the tail latency needs to be kept short to ensure uniform quality of service. In this paper, through experiments on a Cassandra database, we show that long tail latency is caused by a lack of memory space because the database cannot receive any request until free space is reclaimed by writing the buffered data to the storage device. We observed that, since the performance of the storage device determines the amount of time required for writing the buffered data, the performance degradation of Solid State Drive (SSD) due to garbage collection results in a longer tail latency. We propose a garbage collection synchronization technique, called SyncGC, that simultaneously performs garbage collection in the java virtual machine and in the garbage collection in SSD concurrently, thus hiding garbage collection overheads in the SSD. Our evaluations on real SSDs show that SyncGC reduces the tail latency of 99.9<SUP>th</SUP> and, 99.99<SUP>th</SUP>-percentile by 31% and 36%, respectively.