The original PostgreSQL README file is here.

This is an experiment to see what happens if SQL isn't used as a wire protocol for relational database access.

The reasoning is as follows:

• Most sophisticated relational database libraries (including ORMs) store queries internally as expression trees.
• These expression trees are converted to SQL for transmission to a database.
• The database then parses the SQL into an expression tree.
• In theory, the expression tree can be passed directly from the client to the server, rather than going through the intermediate SQL conversion step.

As at the date of writing (12/16/2012) this is a minimally viable proof of concept:

• It can execute simple SQL arithmetic expressions. (E.g. "select 1 + 2;")
• It can select simple columns from tables (no namespacing, etc.) (E.g. "select first_name from users;")
• It can name selected columns (E.g. "select 2 * 5 as result;")

There are two repositories associated with this experiment:

• A modified version of PostgreSQL that can accept a serialized expression tree.
• A modified version of ruby-pg, the ruby client-side interface for PostgreSQL. This component links to customized PostgreSQL libraries that parse SQL to an expression tree, before passing that expression tree to the PostgreSQL server.

To be sure you don't break your existing Postgresql installation, we'll install somewhere else:

export INSTALL_PREFIX="${HOME}/test-postgresql"
export DB_PREFIX="${HOME}/testdb"
export DB_NAME="testdb"

1. Download, unpack and cd

2. Build and install

    export CFLAGS="-g -fPIC"
    autoconf
    ./configure --prefix=${INSTALL_PREFIX} --enable-debug --with-libxml
    make && make install
   

1. Set path PATH="${INSTALL_PREFIX}/bin:$PATH"; export PATH

2. Download, unpack and cd

3. Build and install

    rake install_gem
   

1. Create database initdb -D ${DB_PREFIX}

2. Run postgresql server postgres -D ${DB_PREFIX}

3. Create test table

    psql ${DB_NAME}
    create table test (num integer, str varchar(50));
    insert into test values (14, 'Test');
    ^D
   

irb
require 'pg'
conn = PG.connect( host: "localhost", dbname: ENV["DB_PREFIX"])
x = conn.exec "select * from test;"
x.first

My development system runs FreeBSD 9.0. To build in this environment, you must upgrade GCC (I'm using 4.8).