Allow user to configure default MotherDuck database in postgresql.conf (

#470)

Allow the user to configure a different default MotherDuck database from
`my_db` in `postgresql.conf`. This affords flexibility because there is
currently no user-facing API to change the internal "default" DB in
MotherDuck.

Fixes #459

---------

Co-authored-by: Jelte Fennema-Nio <[email protected]>

README.md

@@ -177,6 +177,12 @@ If you installed `pg_duckdb` in a different Postgres database than the default o
 duckdb.motherduck_postgres_database = 'your_database_name'
 ```
 
+The default MotherDuck database will be easiest to use (see below for details), by default this is `my_db`. If you want to specify which MotherDuck database is your default database, then you can also add the following line to your `postgresql.conf` file:
+
+```ini
+duckdb.motherduck_default_database = 'your_motherduck_database_name'
+```
+
 After doing this (and possibly restarting Postgres). You can then you create tables in the MotherDuck database by using the `duckdb` [Table Access Method][tam] like this:
 ```sql
 CREATE TABLE orders(id bigint, item text, price NUMERIC(10, 2)) USING duckdb;
@@ -189,7 +195,7 @@ CREATE TABLE users_md_copy USING duckdb AS SELECT * FROM users;
 Any tables that you already had in MotherDuck are automatically available in Postgres. Since DuckDB and MotherDuck allow accessing multiple databases from a single connection and Postgres does not, we map database+schema in DuckDB to a schema name in Postgres.
 
 This is done in the following way:
-1. Each schema in your default MotherDuck database are simply merged with the Postgres schemas with the same name.
+1. Each schema in your default MotherDuck database (see above on how to specify which database is the default) are simply merged with the Postgres schemas with the same name.
 2. Except for the `main` DuckDB schema in your default database, which is merged with the Postgres `public` schema.
 3. Tables in other databases are put into dedicated DuckDB-only schemas. These schemas are of the form `ddb$<duckdb_db_name>$<duckdb_schema_name>` (including the literal `$` characters).
 4. Except for the `main` schema in those other databases. That schema should be accessed using the shorter name `ddb$<db_name>` instead.

docs/motherduck.md

@@ -55,7 +55,13 @@ CREATE TABLE users_md_copy USING duckdb AS SELECT * FROM users;
 
 Any tables that you already had in MotherDuck are automatically available in Postgres. Since DuckDB and MotherDuck allow accessing multiple databases from a single connection and Postgres does not, we map database+schema in DuckDB to a schema name in Postgres.
 
-This is done in the following way:
+The default MotherDuck database will be easiest to use (see below for details), by default this is `my_db`. If you want to specify which MotherDuck database is your default database, then you can also add the following line to your `postgresql.conf` file:
+
+```ini
+duckdb.motherduck_default_database = 'your_motherduck_database_name'
+```
+
+The mapping of database+schema to schema name is then done in the following way:
 
 1. Each schema in your default MotherDuck database are simply merged with the Postgres schemas with the same name.
 2. Except for the `main` DuckDB schema in your default database, which is merged with the Postgres `public` schema.

docs/settings.md

@@ -38,6 +38,17 @@ Default: `"postgres"`
 
 Access: General
 
+### `duckdb.motherduck_default_database`
+
+Which MotherDuck database to use as the default database, i.e. the one that
+gets merged with Postgres schemas instead of getting dedicated `ddb$` prefixed
+schemas. The empty string means that pg_duckdb should use the default database
+set by MotherDuck, which is currently always `my_db`.
+
+Default: `""`
+
+Access: Needs to be in the `postgresql.conf` file and requires a restart
+
 ## Security
 
 ### `duckdb.postgres_role`

include/pgduckdb/pgduckdb_guc.h

@@ -11,3 +11,4 @@ extern char *duckdb_motherduck_postgres_database;
 extern int duckdb_motherduck_enabled;
 extern char *duckdb_motherduck_token;
 extern char *duckdb_postgres_role;
+extern char *duckdb_motherduck_default_database;

sql/pg_duckdb--0.1.0--0.2.0.sql

@@ -74,3 +74,6 @@ CREATE PROCEDURE duckdb.recycle_ddb()
 REVOKE ALL ON PROCEDURE duckdb.recycle_ddb() FROM PUBLIC;
 
 ALTER TABLE duckdb.secrets ADD COLUMN scope TEXT;
+
+ALTER TABLE duckdb.tables ADD COLUMN default_database TEXT NOT NULL DEFAULT 'my_db';
+ALTER TABLE duckdb.tables ALTER COLUMN default_database DROP DEFAULT;

src/pgduckdb.cpp

@@ -18,6 +18,7 @@ int duckdb_max_threads_per_postgres_scan = 1;
 int duckdb_motherduck_enabled = MotherDuckEnabled::MOTHERDUCK_AUTO;
 char *duckdb_motherduck_token = strdup("");
 char *duckdb_motherduck_postgres_database = strdup("postgres");
+char *duckdb_motherduck_default_database = strdup("");
 char *duckdb_postgres_role = strdup("");
 
 int duckdb_maximum_threads = -1;
@@ -164,4 +165,8 @@ DuckdbInitGUC(void) {
 
 	DefineCustomVariable("duckdb.motherduck_postgres_database", "Which database to enable MotherDuck support in",
 	                     &duckdb_motherduck_postgres_database);
+
+	DefineCustomVariable("duckdb.motherduck_default_database",
+	                     "Which database in MotherDuck to designate as default (in place of my_db)",
+	                     &duckdb_motherduck_default_database, PGC_POSTMASTER, GUC_SUPERUSER_ONLY);
 }

src/pgduckdb_background_worker.cpp

@@ -682,9 +682,10 @@ SyncMotherDuckCatalogsWithPg_Cpp(bool drop_with_cascade) {
 			continue;
 		}
 
-		Oid arg_types[] = {TEXTOID, TEXTOID};
+		Oid arg_types[] = {TEXTOID, TEXTOID, TEXTOID};
 		Datum values[] = {CStringGetTextDatum(motherduck_db.c_str()),
-		                  CStringGetTextDatum(pgduckdb::current_motherduck_catalog_version)};
+		                  CStringGetTextDatum(pgduckdb::current_motherduck_catalog_version),
+		                  CStringGetTextDatum(default_db.c_str())};
 
 		/*
 		 * We use a cursor here instead of plain SPI_execute, to put a limit on
@@ -695,7 +696,10 @@ SyncMotherDuckCatalogsWithPg_Cpp(bool drop_with_cascade) {
 		Portal deleted_tables_portal =
 		    SPI_cursor_open_with_args(nullptr, R"(
 			SELECT relid::text FROM duckdb.tables
-			WHERE duckdb_db = $1 AND motherduck_catalog_version != $2
+			WHERE duckdb_db = $1 AND (
+				motherduck_catalog_version != $2 OR
+				default_database != $3
+			)
 			)",
 		                              lengthof(arg_types), arg_types, values, NULL, false, 0);
 

src/pgduckdb_ddl.cpp

@@ -281,20 +281,21 @@ DECLARE_PG_FUNCTION(duckdb_create_table_trigger) {
 		int sec_context;
 		const char *postgres_schema_name = get_namespace_name_or_temp(get_rel_namespace(relid));
 		const char *duckdb_db = (const char *)linitial(pgduckdb_db_and_schema(postgres_schema_name, true));
+		auto default_db = pgduckdb::DuckDBManager::Get().GetDefaultDBName();
 		GetUserIdAndSecContext(&saved_userid, &sec_context);
 		SetUserIdAndSecContext(BOOTSTRAP_SUPERUSERID, sec_context | SECURITY_LOCAL_USERID_CHANGE);
 
-		Oid arg_types[] = {OIDOID, TEXTOID, TEXTOID};
-		Datum values[] = {relid_datum, CStringGetTextDatum(duckdb_db), 0};
-		char nulls[] = {' ', ' ', 'n'};
+		Oid arg_types[] = {OIDOID, TEXTOID, TEXTOID, TEXTOID};
+		Datum values[] = {relid_datum, CStringGetTextDatum(duckdb_db), 0, CStringGetTextDatum(default_db.c_str())};
+		char nulls[] = {' ', ' ', 'n', ' '};
 
 		if (pgduckdb::doing_motherduck_sync) {
 			values[2] = CStringGetTextDatum(pgduckdb::current_motherduck_catalog_version);
 			nulls[2] = ' ';
 		}
 		ret = SPI_execute_with_args(R"(
-			INSERT INTO duckdb.tables (relid, duckdb_db, motherduck_catalog_version)
-			VALUES ($1, $2, $3)
+			INSERT INTO duckdb.tables (relid, duckdb_db, motherduck_catalog_version, default_database)
+			VALUES ($1, $2, $3, $4)
 			)",
 		                            lengthof(arg_types), arg_types, values, nulls, false, 0);
 

src/pgduckdb_duckdb.cpp

@@ -15,6 +15,7 @@
 extern "C" {
 #include "postgres.h"
 #include "catalog/namespace.h"
+#include "lib/stringinfo.h"
 #include "utils/lsyscache.h"  // get_relname_relid
 #include "utils/fmgrprotos.h" // pg_sequence_last_value
 #include "common/file_perm.h"
@@ -77,6 +78,24 @@ CreateOrGetDirectoryPath(const char *directory_name) {
 	return duckdb_data_directory;
 }
 
+static char *
+uri_escape(const char *str) {
+	StringInfoData buf;
+	initStringInfo(&buf);
+
+	while (*str) {
+		char c = *str++;
+		if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '-' || c == '_' ||
+		    c == '.' || c == '~') {
+			appendStringInfoChar(&buf, c);
+		} else {
+			appendStringInfo(&buf, "%%%02X", (unsigned char)c);
+		}
+	}
+
+	return buf.data;
+}
+
 namespace ddb {
 bool
 DidWrites() {
@@ -145,10 +164,12 @@ DuckDBManager::Initialize() {
 		 * is not trivial, so for now we simply disable the web login.
 		 */
 		setenv("motherduck_disable_web_login", "1", 1);
+		duckdb_motherduck_default_database = uri_escape(duckdb_motherduck_default_database);
 		if (duckdb_motherduck_token[0] == '\0') {
-			connection_string = "md:";
+			connection_string = psprintf("md:%s", duckdb_motherduck_default_database);
 		} else {
-			connection_string = psprintf("md:?motherduck_token=%s", duckdb_motherduck_token);
+			connection_string =
+			    psprintf("md:%s?motherduck_token=%s", duckdb_motherduck_default_database, duckdb_motherduck_token);
 		}
 	}