Kdb+

Kdb+ is a column-based relational time series database, developed by Kx Systems. Kdb+ database is designed to be used in financial area and store time series data.

History

In 1998, Kx Systems released kdb. Kx Systems then released kdb+ as the 64-bit version in 2003. It is written in q language. Kdb+ is built to process large volume of time-series data in areas including finance and IoT.

Logging

Physical Logging

Kdb+ uses physical logging and WAL. In-memory event-engine will log new data tolog file to ensure durability.

Concurrency Control

Deterministic Concurrency Control

Kdb+ supports deterministic concurrency control.

Isolation Levels

Serializable

Kdb+ only supports SERIALIZABLE isolation level since it uses deterministic concurrency control.

Joins

Hash Join Semi Join

Kdb+ supports sql standard joins. It also supports as-of join and window join.

Data Model

Relational

Kdb+ uses relational model.

Compression

Naïve (Record-Level)

Kdb+ supports on-disk compression with following algorithms:

  • kdb+ algorithm: default compression algorithm

  • gzip: supports different level of compression, larger compression rate needs more computation time

  • Google Snappy: time performance is better but compression rate is lower compared with previous two algorithms

Storage Model

Decomposition Storage Model (Columnar)

Kdb+ uses DSM both for in-memory and on-disk storage.

Query Execution

Vectorized Model

Kdb+ is written in q language and it's vector-based. Each function/operation in the query plan manipulates array/vector data.

Storage Architecture

Hybrid

Kdb+ has both in-memory and on-disk storage. New data is held in memory and old data is flushed to disk. The flush is controlled by event-engine. By default, event-engine will flush in-memory data to disk at daily basis. Rationale behind this design is the system wants to keep everyday new data in memory for fast query.

Indexes

B+Tree

Kdb+ supports both primary and secondary indexes.

Query Interface

SQL HTTP / REST

Kdb+ also supports ODBC/JDBC query interfaces.

Stored Procedures

Supported

Kdb+ supports user to write and store UDF in q language in addition to built-in functions.

Foreign Keys

Supported

Kdb+ supports referential integrity.

System Architecture

Shared-Nothing

Kdb+ uses Lambda architecture on each single node. It has the following properties:

  • Data currently using stores in memory, while historical data is stored on disk.

  • New data come in from streaming sources.

  • Event-engine distribute data to downstream subscribers, including real-time database engine and streaming query engine.

  • Real-time database projects its content down to on-disk historical database for analytic use at daily basis, controlled by event-engine.

Kdb+ Logo
Website

https://kx.com/

Tech Docs

https://code.kx.com/

Developer

Kx Systems

Country of Origin

US

Start Year

1998

Former Name

kdb

Acquired By

First Derivatives plc

Project Type

Commercial

Supported languages

C, C#, C++, Go, Java, JavaScript, Lua, Matlab, Perl, PHP, Python, R, Scala

Operating Systems

Linux, OS X, Solaris, Windows

Licenses

Proprietary

Wikipedia

https://en.wikipedia.org/wiki/Kdb%2B