Review: bLSM:* A General Purpose Log Structured Merge Tree

Big question

LSM tree will sacrifice read performance with write performance. This paper, bLSM ( a Log Structured Merge (LSM) tree with the advantages of B-Trees and log structured approaches), claims to have near optimal read and scan performance, and a bounded write latency with spring and gear merge scheduler.


bLSM is designed as a backing storage for Yahoo’s geographically distributed key-value storage system, and Walnut, a elastic cloud storage system.


Specific question

Reduce read amplification

It seems like they are using fractal tree structure. But the design seems not clear to me. I haven’t get a clue about how they implement the idea.

Write pause

level scheduler: A merge scheduler.

The explanation in the paper is not clear to me. Hard to understand.