Installing PL/V8 in PostgreSQL 9.5

Goal

This is a very straightforward entry. Our only goal in this post is to make sure we have installed PostgreSQL’s PL/V8.

Full Disclosure: Most of this is straight off the GitHub page.

Purpose

Install PL/V8 so that we can use JavaScript to write functions for Postgres and PostGIS. This entry assumes you have a working PostgreSQL v9.2+ installation. If you don’t, check out this tutorial.

Solution

System Info

I’m using…

• OS: Ubuntu 16.04
• PostgreSQL Server 9.5
• PostGIS 2.2 (Not relevant for this process, as long as your version supports PL/v8)

Process

Thanks to apt this installation is very easy! Just run:

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sudo apt install postgresql-9.5-plv8

Check GitHub to see if your PostgreSQL version works with PL/V8. I was able to successfully install PL/V8 for PostgreSQL 9.6 by simply tweaking the version number:

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sudo apt install postgresql-9.6-plv8

After a successful installation, we’ll need to add the language to your database:

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psql -d <database name> -c 'CREATE EXTENSION plv8'

If you use CoffeeScript and LiveScript, you can use plcoffee and plls respectively in place of plv8.

Okay. PL/V8 installed? Check! Language added to the database? Check. Let’s move on to making sure it works.

GitHub says you can use psql -c 'SELECT plv8_version()' to check your version with PL/V8 as of 2.0.0. This did not work for me because at the time of writing the the version in the apt repo is 1:1.4.6.ds-1.

Another method, and perhaps a more direct one, is to 1.) define a simple function and 2.) pass it some dummy data.

First we define a test function:

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CREATE OR REPLACE FUNCTION plv8_test(keys text[], vals text[])
RETURNS text AS $$
  var o = {};
  for(var i=0; i<keys.length; i++){
    o[keys[i]] = vals[i];
  }
  return JSON.stringify(o);
$$ LANGUAGE plv8 IMMUTABLE STRICT;

Second we pass it some dummy data:

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SELECT plv8_test(ARRAY['name', 'age'], ARRAY['Tom', '29']);

If successful, you should see this response:

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         plv8_test
---------------------------
 {"name":"Tom","age":"29"}
(1 row)

Conclusions

According to this post from Regina Obe, PL/V8 is great for Map Algebra. Unfortunately, as with most posts I’ve found about the PostGIS Raster Module, fails to use a geographically relevant example of raster analysis. I attempt to remedy that with this series of posts on writing ST_MapAlgebra callback functions, but I’m yet to try any with PL/V8 yet.