nessDB

nessDB is an embedded key-value DBMS written in ANSI C with BSD license. It does not require any external dependencies and works in most POSIX systems. As for storage engine, nessDB used LSM-tree (Log-Structured Merge Tree) in v1.8, B-epsilon-tree in v2.0, and will use fractal-tree in v3.0. nessDB also used fractional cascading to speed up query.

History

It has released two main versions (v1.8 and v2.0), while v3.0 is still work in progress.

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.

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.

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.

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.

Foreign Keys

Not Supported

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

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.

Isolation Levels

Serializable

nessDB v3.0 support four isolation levels: read uncommitted, read committed, repeatable read and serializable.

Joins

Not Supported

nessDB does not support join. It is a key-value DBMS with only interfaces such as SET, GET, DEL, EXISTS.

Query Execution

Tuple-at-a-Time Model

nessDB is a key-value DBMS and each query only involves a single key-value pair.

Query Interface

Custom API

nessDB is an embedded DBMS with custom C API, as well as wrappers for Java, Python and Lua.

Storage Architecture

Disk-oriented

nessDB is a disk-oriented DBMS. All data are stored in nonvalatile storage after shutdown.

Storage Model

N-ary Storage Model (Row/Record)

nessDB v2.0 used a Small-Splittable Tree (SST), a variant of B-Epsilon-tree, for storage engine. SST has multiple levels with exponential expanding size. For level0, the data is un-sorted and the other levels are sorted. This data structure has good performance for random write.

Storage Organization

Heaps

For a tree node file, there is a header which stored the key-value pair in each level. And the header is followed by several var-length key-value pairs with data-offset.

Stored Procedures

Not Supported

System Architecture

Embedded

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nessDB Logo
Website

https://github.com/BohuTANG/nessDB

Source Code

https://github.com/BohuTANG/nessDB

Tech Docs

https://github.com/BohuTANG/nessDB/wiki

Developer

Bohu Tang

Country of Origin

CN

Start Year

2011

End Year

2016

Project Type

Open Source

Written in

C

Supported languages

C, C++, Java, Lua, Python

Operating Systems

BSD, Linux

Licenses

BSD

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