Configuration Constants

Common Constants

Constant	Purpose
DB_ENGINE	Database backend. Accepts sqlite, postgresql, duckdb, and aliases such as postgres, pgsql, duck, and sqlite3.
DATABASE_ENGINE	Backward-compatible database engine constant.
DB_DIR	Directory used by file-backed engines.
DB_FILE	SQLite database file name.

DuckDB Storage Constants

The setup CLI can write the common DuckDB storage constants for you with --duckdb-backend, --duckdb-external-storage-dir, and --duckdb-working-database-file.

Constant	Purpose
DUCKDB_FILE	Native DuckDB database file name.
DUCKDB_BACKEND	Backend name. Built-in presets: parquet, csv, json. Any other name uses custom SQL templates.
DUCKDB_EXTERNAL_STORAGE_DIR	Directory or URI prefix that stores one file per WordPress table, such as wp_options.parquet.
DUCKDB_WORKING_DATABASE_FILE	Mutable DuckDB working database. Keep this even for external backends.
DUCKDB_METADATA_MANIFEST_FILE	Optional local file for WordPress schema/index metadata.
DUCKDB_BACKEND_FILE_EXTENSION	File extension for path-based custom backends, such as psv or parquet.
DUCKDB_BACKEND_READ_SQL	SQL relation template used to hydrate one local working table.
DUCKDB_BACKEND_WRITE_SQL	SQL statement template used to flush one local working table.
DUCKDB_BACKEND_SETUP_SQL	SQL statements to run after connecting, such as INSTALL, LOAD, CREATE SECRET, or ATTACH.
DUCKDB_BACKEND_TABLES	Explicit table list for remote/object/attached backends that PHP cannot discover by scanning a local directory.
DUCKDB_BACKEND_ATOMIC_FLUSH	Whether to write local path-based output to a temporary file first. Defaults to on for local paths and off for URIs.

DuckDB Connection Constants

Constant	Purpose
DUCKDB_PHP_AUTOLOAD	Composer autoload path for the DuckDB PHP client.
DUCKDB_CONNECTION	Native DuckDB file connection mode: ffi, embedded, unix, tcp, http, or sidecar.
DUCKDB_REMOTE_SOCKET	Unix socket path for DUCKDB_CONNECTION=unix.
DUCKDB_REMOTE_HOST / DUCKDB_REMOTE_PORT	Host and port for DUCKDB_CONNECTION=tcp.
DUCKDB_REMOTE_URL	HTTP endpoint for DUCKDB_CONNECTION=http.
DUCKDB_SIDECAR_COMMAND	Stdio sidecar command for DUCKDB_CONNECTION=sidecar.
DUCKDB_CONNECTION_SETUP_SQL	Optional SQL string or array of SQL strings to run on each DuckDB connection, such as SET threads=2.
WP_DUCKDB_CONNECTION_SETUP_SQL_JSON	Environment variable form for sidecar process setup SQL.
WP_DUCKDB_REQUEST_TRANSACTION	Optional performance flag. Set to 1 to batch request writes into one DuckDB transaction.

SQL Template Placeholders

Placeholder	Replaced with
{table} or {table_identifier}	The local DuckDB table as a quoted identifier, for example "wp_options".
{table_name}	The table name as a quoted string literal, for example 'wp_options'.
{path} or {source}	The per-table path or URI as a quoted string literal, for example 's3://bucket/wp/wp_options.parquet'.

External storage metadata is stored outside formats such as JSON, CSV, and Parquet because those formats do not preserve all MySQL DDL semantics by themselves.