Community version of the PostgreSQL multi-purpose Ruby Foreign Data Wrapper
C Ruby Shell Makefile C++
Switch branches/tags
Nothing to show
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Permalink
Failed to load latest commit information.
builtin_wrappers/holycorn-redis
config
examples
tests
.gitignore
.travis.yml
Changelog
Dockerfile
HISTORY.md
LICENSE.md
META.json
Makefile
README.md
Rakefile
execution_state.h
holycorn--1.0.sql
holycorn.c
holycorn.control
options.h
plan_state.h

README.md

Holycorn: PostgreSQL multi-purpose Ruby data wrapper Travis

(m)Ruby + PostgreSQL = <3

Holycorn makes it easy to implement a Foreign Data Wrapper using Ruby.

It is based on top of mruby, that provides sandboxing capabilities the regular Ruby VM "MRI/CRuby" does not implement.

Join the chat at https://gitter.im/franckverrot/holycorn

Built-in Wrappers

Holycorn is the combination of the mruby VM, some supporting gems (some basic libraries and some more advanced ones), and custom code that implement the actual foreign data wrappers.

All the following wrappers are currently linked against Holycorn:

  • Redis, using the mruby-redis gem

INSTALLATION

Prerequisites

  • PostgreSQL 9.1+

Setup

Simply run

rake

to vendor and build mruby.

Now that mruby is built, building holycorn requires to run

make

and installing it only requires to run

make install

Now connect to PostgreSQL and install the extension:

λ psql
psql (9.4.1)
Type "help" for help.

DROP EXTENSION holycorn CASCADE;
CREATE EXTENSION holycorn;

Using Builtin Foreign Data Wrappers

A set of builtin FDW are distributed with Holycorn for an easy setup. All one needs to provide are the options that will allow the FDW to be configured:

λ psql
psql (9.4.1)
Type "help" for help.

CREATE SERVER holycorn_server FOREIGN DATA WRAPPER holycorn;
CREATE FOREIGN TABLE redis_table (key text, value text)
  SERVER holycorn_server
  OPTIONS (wrapper_class 'HolycornRedis', host '127.0.0.1', port '6379', db '0');

As Holycorn doesn't support INSERTs yet, let's create some manually:

λ redis-cli
127.0.0.1:6379> select 0
OK
127.0.0.1:6379> keys *
(empty list or set)
127.0.0.1:6379> set foo 1
OK
127.0.0.1:6379> set bar 2
OK
127.0.0.1:6379> set baz 3
OK
127.0.0.1:6379> keys *
1) "bar"
2) "foo"
3) "baz"

Now that the table has been created and we have some data in Redis, we can select data from the foreign table.

SELECT * from redis_table;

 key | value
-----+-------
 bar | 2
 foo | 1
 baz | 3
(3 rows)

Using custom scripts

Alternatively, custom scripts can be used as the source for a Foreign Data Wrapper:

DROP EXTENSION holycorn CASCADE;
CREATE EXTENSION holycorn;
CREATE SERVER holycorn_server FOREIGN DATA WRAPPER holycorn;
CREATE FOREIGN TABLE holytable (some_date timestamptz) \
  SERVER holycorn_server
  OPTIONS (wrapper_path '/tmp/source.rb');

And the source file of the wrapper:

# /tmp/source.rb
class Producer
  def initialize(env = {}) # env contains informations provided by Holycorn
  end

  def each
    @enum ||= Enumerator.new do |y|
      10.times do |t|
        y.yield [ Time.now ]
      end
    end
    @enum.next
  end
  self
end

Now you can select data out of the wrapper:

λ psql
psql (9.4.1)
Type "help" for help.

franck=# SELECT * FROM holytable;
      some_date
---------------------
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
(10 rows)

Pretty neat.

SUPPORTED SCRIPTS

General rules

Any type of Ruby object can act as a FDW. The only requirements are that it can receive .new (with arity = 1) and return an object that can receive each (arity = 0).

It doesn't have to be a Class, and there's currently no will to provide a superclass to be inherited from.

In future versions, there will be many more callbacks to interact with PG's FDW infrastructure through Holycorn.

Also, the script can only be a single word - like MyClass - as long as MyClass has been defined and exists within your compilation of mruby.

Environment

A hash is passed by Holycorn to the Ruby script. Its current keys are:

  • PG_VERSION
  • PG_VERSION_NUM
  • PACKAGE_STRING
  • PACKAGE_VERSION
  • MRUBY_RUBY_VERSION
  • WRAPPER_PATH

SUPPORTED TYPES (Ruby => PG)

Builtin types

  • MRB_TT_FREE => null
  • MRB_TT_FALSE => Boolean
  • MRB_TT_TRUE => Boolean
  • MRB_TT_FIXNUM => Int64
  • MRB_TT_SYMBOL => Text
  • MRB_TT_UNDEF => Unsupported
  • MRB_TT_FLOAT => Float8
  • MRB_TT_CPTR => Unsupported
  • MRB_TT_OBJECT => Text (to_s is called)
  • MRB_TT_CLASS => Text (class.to_s is called)
  • MRB_TT_MODULE => Text (to_s is called)
  • MRB_TT_ICLASS => Unsupported
  • MRB_TT_SCLASS => Unsupported
  • MRB_TT_PROC => Text (inspect is called)
  • MRB_TT_ARRAY => Text (inspect is called)
  • MRB_TT_HASH => Text (inspect is called)
  • MRB_TT_STRING => Text
  • MRB_TT_RANGE => Text (inspect is called)
  • MRB_TT_EXCEPTION => Unsupported
  • MRB_TT_FILE => Unsupported
  • MRB_TT_ENV => Unsupported
  • MRB_TT_DATA => See "Arbitraty Ruby objects" section
  • MRB_TT_FIBER => Text (inspect is called)
  • MRB_TT_MAXDEFINE => Unsupported

Arbitraty Ruby objects

  • Time (Ruby) => timestamptz

CONFIGURATION

Server

None (yet).

Foreign Table

Either wrapper_class or wrapper_path can be used to defined whether an external script or a built-in wrapper will manage the foreign table.

  • wrapper_class: Name of the built-in wrapper class
  • wrapper_path: Path of a custom script

In both case, any other option will be pushed down to the wrapper class via the constructor.

TODO

  • Array type
  • JSON type
  • Range type
  • Support PG 9.5's IMPORT FOREIGN SCHEMA for easy setup

Note on Patches/Pull Requests

  • Fork the project.
  • Make your feature addition or bug fix.
  • Add tests for it. This is important so I don't break it in a future version unintentionally.
  • Commit, do not mess with version or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
  • Send me a pull request. Bonus points for topic branches.

LICENSE

Copyright (c) 2015-2017 Franck Verrot

Holycorn is an Open Source project licensed under the terms of the LGPLv3 license. Please see http://www.gnu.org/licenses/lgpl-3.0.html for license text.

Holycorn Pro has a commercial-friendly license allowing private forks and modifications of Holycorn. Please see http://holycorn.org/pro/ or email at franck @ holycorn . org for more details. You can find the commercial license terms in COMM-LICENSE.

AUTHOR

Franck Verrot, @franckverrot