Datahike database configuration

At database creation datahike supports features that can be configured based on the application's requirements. As of version 0.2.0 configuration for the storage backend, the schema flexibility, and the time variance is supported. Be aware: all these features can be set at database creation but can not be changed afterwards.

Storage Backend

The backend configuration can be encoded within a base uri we can connect to. It has the following scheme:

datahike:<backend>://(<username>:<password>@)<host>:<port><path>

Each backend needs a different set of provided parameters. See definition below for further information. For simple and fast creation you can simple type:

(:require '[datahike.api :as d])
(def uri "datahike:mem://example")
(d/create-database uri)

If you prefer data structures for configuration you may use a hash map. The example above looks like:

(:require '[datahike.api :as d])
(def config {:backend :mem :host "example"})
(d/create-database config)

At the moment we support four different backends: in-memory ,file-based, LevelDB, and PostgreSQL.

in-memory

• <backend>: mem
• host: name of the database
• uri example: datahike:mem://mem-example
• hash map example: {:backend :mem :host "mem-example"}

file-based

• <backend>: file
• path: absolute path to the storage folder
• uri example: datahike:file:///tmp/file-example
• hash map example: {:backend :file :path "/tmp/file-example"}

LevelDB

• <backend>: level
• path: absolute path to the LevelDB instance
• uri example: datahike:level:///tmp/level-example
• hash map example: {:backend :level :path "/tmp/level-example"}

PostgreSQL

• <backend>: pg
• username: PostgreSQL instance username
• password: PostgreSQL instance password
• host: PostgreSQL instance host
• port: PostgreSQL instance port
• path: name of the PostgreSQL database, must be present in the instance
• uri example: datahike:pg://alice:foobar@localhost:5432/pg_example
• hash map example: {:backend :pg :host "localhost" :port 5432 :username "alice" :password "foobar" :path "/pg_example"}

Schema Flexibility

By default the datahike api uses a schema-on-write approach with strict value types that need to be defined in advance. If you are not sure how your data model looks like and you want to transact any kind of data into the database you can set schema-on-read to true by adding it as optional parameter at database creation. You may add basic schema definitions like :db/unique, :db/cardinality or db.type/ref where these kind of structure is needed.

(:require '[datahike.api :as d])
(d/create-database "datahike:mem://example" :schema-on-read true)

Have a look at the schema documentation for more information.

Time Variance

Datahike has the capability to inspect and query historical data within temporal indices. If your application does not require any temporal data, you may set :temporal-index to false.

(:require '[datahike.api :as d])
(d/create-database "datahike:mem://example" :temporal-index false)

Be aware: when deactivating the temporal index you may not use any temporal databases like history, as-of, or since.

Refer to the time variance documentation for more information.