Reviewed Article: LevelDB and Node: What is LevelDB Anyway?

From this article, the keys takeaway for me are 1) the high-level overview of the architecture of LevelDB and 2) How other systems can use LevelDB as the backing store.

The architecture of the LevelDB is similar to the storage component described in the Google BigTable architecture. It uses SSTable and LSM to provide data access to the underlying physical storage. The design aims to maximize the usage of disk throughput while providing CRUD operations. SSTable is a disk-based immutable data structure that is organized in such a way that allows reading a single key or a group of sorted keys by a single disk seek. With the combination of LSM, it supports create, update and delete operations.

The section that I found the most interesting is "Table File Hierarchy". It describes how LevelDB organizes the SSTable files. It does exactly what LevelDB name suggests: LEVEL. The SSTable files are organized into levels: The top level (level 0) contains small SSTable files and each level down contains file size bigger than the previous level. This organization of data makes the new data available on the top level while the older data is aggregated and stored in the lower levels.

Node.js makes use of LevelDB for their backing store because LevelDB provides a way for Node to stream a set of sorted-key data very efficiently.

LevelDB can be best used with Gecko, a contention-oblivious disk array which separates write and read workload by intelligently allocating disks for write only while read workloads are spread to other disks with the help of caches for reading from the write-only disks.