Foreign Keys

Not Supported

nessDB is a key-value DBMS so it does not support foreign key.

Storage Model

N-ary Storage Model (Row/Record)

Concurrency Control

Two-Phase Locking (Deadlock Detection)

nessDB v3.0 will use two-phase locking with deadlock detection, but this part does not finish yet. For deadlock detection, nessDB v3.0 will use Helgrind, a thread error detector that can detect potential deadlocks arising from lock ordering problems.

For nessDB v2.0, it is a single-thread engine. The engine can process a single request at a time.

Compression

Naïve (Page-Level)

nessDB v3.0 used Snappy, a data compression and decompression library written in C++ by Google, to compress the buffered-tree node data when serializing the node to disk and decompress it when deserializing. nessDB v2.0 used QuickLZ, a compression library written in C, to compress the key-value pair.

System Architecture

Embedded

Data Model

Key/Value

nessDB is a key-value DBMS, which supports Redis-like protocol, such as SET, GET, DEL, EXISTS. To be specific, both key and value are general raw data and are represented by a pointer with length.

Storage Architecture

Disk-oriented

Indexes

Log-Structured Merge Tree

nessDB used LSM-tree (Log-Structured Merge Tree) in v1.8, Small-Splittable Tree in v2.0, and will use fractal-tree in v3.0 for key-value storage. Those data structures are suitable for high-performance insertion compared to B-tree.

Checkpoints

Blocking

It does not fully support no redo log and recovery. nessDB v3.0 will support sharp checkpoint with a 60 seconds period according to the code, but the recovery part has not been finished.