rdbms: avoid connections on more lazy DBConnRef methods

Also:
* Fixed LoadBalancer::getAnyOpenConnection for both
  DB_MASTER and DB_REPLICA, which are not real indexes.
* Lock down DBConnRef::close since it can only cause trouble.
* Relax DBConnRef restrictions on tablePrefix()/dbSchema()
  for the harmless "getter" mode case.
* Remove redundant DatabasePostgres::getServer definition.

Change-Id: Ia855d901cc3c28147e52284fdabb1645805d4466

includes/libs/rdbms/database/DBConnRef.php

@@ -74,11 +74,27 @@ class DBConnRef implements IDatabase {
 	}
 
 	public function tablePrefix( $prefix = null ) {
+		if ( $this->conn === null && $prefix === null ) {
+			$domain = DatabaseDomain::newFromId( $this->params[self::FLD_DOMAIN] );
+			// Avoid triggering a database connection
+			return $domain->getTablePrefix();
+		} elseif ( $this->conn !== null && $prefix === null ) {
+			// This will just return the prefix
+			return $this->__call( __FUNCTION__, func_get_args() );
+		}
 		// Disallow things that might confuse the LoadBalancer tracking
 		throw new DBUnexpectedError( $this, "Database selection is disallowed to enable reuse." );
 	}
 
 	public function dbSchema( $schema = null ) {
+		if ( $this->conn === null && $schema === null ) {
+			$domain = DatabaseDomain::newFromId( $this->params[self::FLD_DOMAIN] );
+			// Avoid triggering a database connection
+			return $domain->getSchema();
+		} elseif ( $this->conn !== null && $schema === null ) {
+			// This will just return the schema
+			return $this->__call( __FUNCTION__, func_get_args() );
+		}
 		// Disallow things that might confuse the LoadBalancer tracking
 		throw new DBUnexpectedError( $this, "Database selection is disallowed to enable reuse." );
 	}
@@ -235,7 +251,7 @@ class DBConnRef implements IDatabase {
 	}
 
 	public function close() {
-		return $this->__call( __FUNCTION__, func_get_args() );
+		throw new DBUnexpectedError( $this->conn, 'Cannot close shared connection.' );
 	}
 
 	public function query( $sql, $fname = __METHOD__, $tempIgnore = false ) {
@@ -385,6 +401,12 @@ class DBConnRef implements IDatabase {
 	}
 
 	public function getDBname() {
+		if ( $this->conn === null ) {
+			$domain = DatabaseDomain::newFromId( $this->params[self::FLD_DOMAIN] );
+			// Avoid triggering a database connection
+			return $domain->getDatabase();
+		}
+
 		return $this->__call( __FUNCTION__, func_get_args() );
 	}
 

includes/libs/rdbms/database/DatabasePostgres.php

@@ -1346,10 +1346,6 @@ SQL;
 		return [ $startOpts, $useIndex, $preLimitTail, $postLimitTail, $ignoreIndex ];
 	}
 
-	public function getServer() {
-		return $this->server;
-	}
-
 	public function buildConcat( $stringList ) {
 		return implode( ' || ', $stringList );
 	}

includes/libs/rdbms/loadbalancer/LoadBalancer.php

@@ -566,15 +566,24 @@ class LoadBalancer implements ILoadBalancer {
 	}
 
 	public function getAnyOpenConnection( $i, $flags = 0 ) {
+		$i = ( $i === self::DB_MASTER ) ? $this->getWriterIndex() : $i;
 		$autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
+
 		foreach ( $this->conns as $connsByServer ) {
-			if ( !isset( $connsByServer[$i] ) ) {
-				continue;
+			if ( $i === self::DB_REPLICA ) {
+				$indexes = array_keys( $connsByServer );
+			} else {
+				$indexes = isset( $connsByServer[$i] ) ? [ $i ] : [];
 			}
 
-			foreach ( $connsByServer[$i] as $conn ) {
-				if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
-					return $conn;
+			foreach ( $indexes as $index ) {
+				foreach ( $connsByServer[$index] as $conn ) {
+					if ( !$conn->isOpen() ) {
+						continue; // some sort of error occured?
+					}
+					if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
+						return $conn;
+					}
 				}
 			}
 		}

tests/phpunit/includes/libs/rdbms/database/DBConnRefTest.php

@@ -44,7 +44,27 @@ class DBConnRefTest extends PHPUnit\Framework\TestCase {
 			->disableOriginalConstructor()
 			->getMock();
 
-		$db->method( 'select' )->willReturn( new FakeResultWrapper( [] ) );
+		$open = true;
+		$db->method( 'select' )->willReturnCallback( function () use ( &$open ) {
+			if ( !$open ) {
+				throw new LogicException( "Not open" );
+			}
+
+			return new FakeResultWrapper( [] );
+		} );
+		$db->method( 'close' )->willReturnCallback( function () use ( &$open ) {
+			$open = false;
+
+			return true;
+		} );
+		$db->method( 'isOpen' )->willReturnCallback( function () use ( &$open ) {
+			return $open;
+		} );
+		$db->method( 'open' )->willReturnCallback( function () use ( &$open ) {
+			$open = true;
+
+			return $open;
+		} );
 		$db->method( '__toString' )->willReturn( 'MOCK_DB' );
 
 		return $db;
@@ -122,6 +142,9 @@ class DBConnRefTest extends PHPUnit\Framework\TestCase {
 		$this->assertSame( 'dummy', $ref->getDomainID() );
 	}
 
+	/**
+	 * @covers Wikimedia\Rdbms\DBConnRef::select
+	 */
 	public function testSelect() {
 		// select should get passed through normally
 		$ref = $this->getDBConnRef();
@@ -137,4 +160,13 @@ class DBConnRefTest extends PHPUnit\Framework\TestCase {
 		$this->assertInternalType( 'string', $ref->__toString() );
 	}
 
+	/**
+	 * @covers Wikimedia\Rdbms\DBConnRef::close
+	 * @expectedException \Wikimedia\Rdbms\DBUnexpectedError
+	 */
+	public function testClose() {
+		$lb = $this->getLoadBalancerMock();
+		$ref = new DBConnRef( $lb, [ DB_REPLICA, [], 'dummy', 0 ] );
+		$ref->close();
+	}
 }