Add PostgreSQL database driver

[adamziel]

Big picture

Adds PostgreSQL backend support alongside the existing SQLite backend.

WordPress core unit tests pass to the same extent as with the SQLite backend.

Implementation checkpoints

• PostgreSQL UDF rewrite checkpoint: e1b0bacfe9cd7dc12c2ab0927e7e1a7c73c53cb7 (Rewrite MySQL UDF calls for PostgreSQL).

Try it on a fresh WordPress site

Prerequisites: pdo and pdo_pgsql enabled in PHP.

Install the plugin files into the WordPress site:

export REPO=/path/to/sqlite-database-integration
export WP_ROOT=/path/to/wordpress

mkdir -p "$WP_ROOT/wp-content/plugins/sqlite-database-integration"
rsync -a --delete \
  "$REPO/packages/plugin-sqlite-database-integration/" \
  "$WP_ROOT/wp-content/plugins/sqlite-database-integration/"

# Replace the development symlink with a real copy of the shared database package:
rm -rf "$WP_ROOT/wp-content/plugins/sqlite-database-integration/wp-includes/database"
cp -R \
  "$REPO/packages/mysql-on-sqlite/src" \
  "$WP_ROOT/wp-content/plugins/sqlite-database-integration/wp-includes/database"

Install the WordPress database drop-in:

cp \
  "$WP_ROOT/wp-content/plugins/sqlite-database-integration/db.copy" \
  "$WP_ROOT/wp-content/db.php"

php -r '$file = getenv( "WP_ROOT" ) . "/wp-content/db.php"; $contents = file_get_contents( $file ); $contents = str_replace( array( "'{SQLITE_IMPLEMENTATION_FOLDER_PATH}'", "{SQLITE_PLUGIN}" ), array( "__DIR__ . \"/plugins/sqlite-database-integration\"", "sqlite-database-integration/load.php" ), $contents ); file_put_contents( $file, $contents );'

Configure the database access in wp-config.php:

define( 'DB_ENGINE', 'postgresql' );

define( 'DB_NAME', 'wordpress' );
define( 'DB_USER', 'wordpress' );
define( 'DB_PASSWORD', 'password' );
define( 'DB_HOST', '127.0.0.1:5432' );
define( 'DB_CHARSET', 'utf8mb4' );
define( 'DB_COLLATE', '' );

Then open the site in a browser and run the normal WordPress installer at /wp-admin/install.php. The wp-content/db.php drop-in loads the PostgreSQL wpdb adapter before install, and the PostgreSQL install hooks translate the WordPress schema for PostgreSQL.

After install, a quick smoke test is enough to confirm the site is using the PostgreSQL adapter:

<?php
require __DIR__ . '/wp-load.php';
var_dump( DB_ENGINE );
var_dump( get_class( $GLOBALS['wpdb'] ) );

Expected output includes:

postgresql
WP_PostgreSQL_DB

Repo test environment

The repo still has a supported generated test environment for CI and local parity work:

WP_TEST_DB_BACKEND=postgresql composer run wp-setup
WP_TEST_DB_BACKEND=postgresql composer run wp-test-php
WP_TEST_DB_BACKEND=postgresql composer run wp-test-e2e

Those commands generate the WordPress checkout, Docker override, test configs, drop-in wiring, and node dependencies used by CI. They are useful for repeatable testing, but they are not required to try PostgreSQL on a fresh WordPress site.