20.1. SPI Overview
When you implement a new Presto plugin, you implement interfaces and override methods defined by the SPI.
Plugins can provide additional Connectors, Types, Functions and System Access Control. In particular, connectors are the source of all data for queries in Presto: they back each catalog available to Presto.
The SPI source can be found in the
presto-spi directory in the
root of the Presto source tree.
Each plugin identifies an entry point: an implementation of the
Plugin interface. This class name is provided to Presto via
the standard Java
ServiceLoader interface: the classpath contains
a resource file named
com.facebook.presto.spi.Plugin in the
META-INF/services directory. The content of this file is a
single line listing the name of the plugin class:
For a built-in plugin that is included in the Presto source code,
this resource file is created whenever the
pom.xml file of a plugin
contains the following line:
Plugin interface is a good starting place for developers looking
to understand the Presto SPI. It contains access methods to retrieve
various classes that a Plugin can provide. For example, the
method is a top-level function that Presto calls to retrieve a
ConnectorFactory when Presto
is ready to create an instance of a connector to back a catalog. There are similar
Building Plugins via Maven
Plugins depend on the SPI from Presto:
<dependency> <groupId>com.facebook.presto</groupId> <artifactId>presto-spi</artifactId> <scope>provided</scope> </dependency>
The plugin uses the Maven
provided scope because Presto provides
the classes from the SPI at runtime and thus the plugin should not
include them in the plugin assembly.
There are a few other dependencies that are provided by Presto, including Slice and Jackson annotations. In particular, Jackson is used for serializing connector handles and thus plugins must use the annotations version provided by Presto.
All other dependencies are based on what the plugin needs for its own implementation. Plugins are loaded in a separate class loader to provide isolation and to allow plugins to use a different version of a library that Presto uses internally.
For an example
pom.xml file, see the example HTTP connector in the
presto-example-http directory in the root of the Presto source tree.
Deploying a Custom Plugin
In order to add a custom plugin to a Presto installation, create a directory
for that plugin in the Presto plugin directory and add all the necessary jars
for the plugin to that directory. For example, for a plugin called
my-functions, you would create a directory
my-functions in the Presto
plugin directory and add the relevant jars to that directory.
By default, the plugin directory is the
plugin directory relative to the
directory in which Presto is installed, but it is configurable using the
plugin.config-dir. In order for Presto to pick up
the new plugin, you must restart Presto.
Plugins must be installed on all nodes in the Presto cluster (coordinator and workers).