diff --git a/src/Database/DBA.php b/src/Database/DBA.php
new file mode 100644
index 0000000000..28eedec151
--- /dev/null
+++ b/src/Database/DBA.php
@@ -0,0 +1,1522 @@
+<?php
+
+namespace Friendica\Database;
+
+// Do not use Core\Config in this class at risk of infinite loop.
+// Please use App->getConfigVariable() instead.
+//use Friendica\Core\Config;
+
+use Friendica\Core\System;
+use Friendica\Util\DateTimeFormat;
+
+/**
+ * @class MySQL database class
+ *
+ * This class is for the low level database stuff that does driver specific things.
+ */
+class dba
+{
+	public static $connected = false;
+
+	private static $server_info = '';
+	private static $db;
+	private static $driver;
+	private static $error = false;
+	private static $errorno = 0;
+	private static $affected_rows = 0;
+	private static $in_transaction = false;
+	private static $in_retrial = false;
+	private static $relation = [];
+	private static $db_serveraddr = '';
+	private static $db_user = '';
+	private static $db_pass = '';
+	private static $db_name = '';
+	private static $db_charset = '';
+
+	public static function connect($serveraddr, $user, $pass, $db, $charset = null)
+	{
+		if (!is_null(self::$db) && self::connected()) {
+			return true;
+		}
+
+		// We are storing these values for being able to perform a reconnect
+		self::$db_serveraddr = $serveraddr;
+		self::$db_user = $user;
+		self::$db_pass = $pass;
+		self::$db_name = $db;
+		self::$db_charset = $charset;
+
+		$serveraddr = trim($serveraddr);
+
+		$serverdata = explode(':', $serveraddr);
+		$server = $serverdata[0];
+
+		if (count($serverdata) > 1) {
+			$port = trim($serverdata[1]);
+		}
+
+		$server = trim($server);
+		$user = trim($user);
+		$pass = trim($pass);
+		$db = trim($db);
+		$charset = trim($charset);
+
+		if (!(strlen($server) && strlen($user))) {
+			return false;
+		}
+
+		if (class_exists('\PDO') && in_array('mysql', PDO::getAvailableDrivers())) {
+			self::$driver = 'pdo';
+			$connect = "mysql:host=".$server.";dbname=".$db;
+
+			if (isset($port)) {
+				$connect .= ";port=".$port;
+			}
+
+			if ($charset) {
+				$connect .= ";charset=".$charset;
+			}
+
+			try {
+				self::$db = @new PDO($connect, $user, $pass);
+				self::$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
+				self::$connected = true;
+			} catch (PDOException $e) {
+			}
+		}
+
+		if (!self::$connected && class_exists('mysqli')) {
+			self::$driver = 'mysqli';
+			self::$db = @new mysqli($server, $user, $pass, $db, $port);
+			if (!mysqli_connect_errno()) {
+				self::$connected = true;
+
+				if ($charset) {
+					self::$db->set_charset($charset);
+				}
+			}
+		}
+
+		// No suitable SQL driver was found.
+		if (!self::$connected) {
+			self::$driver = null;
+			self::$db = null;
+		}
+
+		return self::$connected;
+	}
+
+	/**
+	 * Disconnects the current database connection
+	 */
+	public static function disconnect()
+	{
+		if (is_null(self::$db)) {
+			return;
+		}
+
+		switch (self::$driver) {
+			case 'pdo':
+				self::$db = null;
+				break;
+			case 'mysqli':
+				self::$db->close();
+				self::$db = null;
+				break;
+		}
+	}
+
+	/**
+	 * Perform a reconnect of an existing database connection
+	 */
+	public static function reconnect() {
+		self::disconnect();
+
+		$ret = self::connect(self::$db_serveraddr, self::$db_user, self::$db_pass, self::$db_name, self::$db_charset);
+		return $ret;
+	}
+
+	/**
+	 * Return the database object.
+	 * @return PDO|mysqli
+	 */
+	public static function get_db()
+	{
+		return self::$db;
+	}
+
+	/**
+	 * @brief Returns the MySQL server version string
+	 *
+	 * This function discriminate between the deprecated mysql API and the current
+	 * object-oriented mysqli API. Example of returned string: 5.5.46-0+deb8u1
+	 *
+	 * @return string
+	 */
+	public static function server_info() {
+		if (self::$server_info == '') {
+			switch (self::$driver) {
+				case 'pdo':
+					self::$server_info = self::$db->getAttribute(PDO::ATTR_SERVER_VERSION);
+					break;
+				case 'mysqli':
+					self::$server_info = self::$db->server_info;
+					break;
+			}
+		}
+		return self::$server_info;
+	}
+
+	/**
+	 * @brief Returns the selected database name
+	 *
+	 * @return string
+	 */
+	public static function database_name() {
+		$ret = self::p("SELECT DATABASE() AS `db`");
+		$data = self::inArray($ret);
+		return $data[0]['db'];
+	}
+
+	/**
+	 * @brief Analyze a database query and log this if some conditions are met.
+	 *
+	 * @param string $query The database query that will be analyzed
+	 */
+	private static function logIndex($query) {
+		$a = get_app();
+
+		if (!$a->getConfigVariable('system', 'db_log_index')) {
+			return;
+		}
+
+		// Don't explain an explain statement
+		if (strtolower(substr($query, 0, 7)) == "explain") {
+			return;
+		}
+
+		// Only do the explain on "select", "update" and "delete"
+		if (!in_array(strtolower(substr($query, 0, 6)), ["select", "update", "delete"])) {
+			return;
+		}
+
+		$r = self::p("EXPLAIN ".$query);
+		if (!DBM::is_result($r)) {
+			return;
+		}
+
+		$watchlist = explode(',', $a->getConfigVariable('system', 'db_log_index_watch'));
+		$blacklist = explode(',', $a->getConfigVariable('system', 'db_log_index_blacklist'));
+
+		while ($row = self::fetch($r)) {
+			if ((intval($a->getConfigVariable('system', 'db_loglimit_index')) > 0)) {
+				$log = (in_array($row['key'], $watchlist) &&
+					($row['rows'] >= intval($a->getConfigVariable('system', 'db_loglimit_index'))));
+			} else {
+				$log = false;
+			}
+
+			if ((intval($a->getConfigVariable('system', 'db_loglimit_index_high')) > 0) && ($row['rows'] >= intval($a->getConfigVariable('system', 'db_loglimit_index_high')))) {
+				$log = true;
+			}
+
+			if (in_array($row['key'], $blacklist) || ($row['key'] == "")) {
+				$log = false;
+			}
+
+			if ($log) {
+				$backtrace = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);
+				@file_put_contents($a->getConfigVariable('system', 'db_log_index'), DateTimeFormat::utcNow()."\t".
+						$row['key']."\t".$row['rows']."\t".$row['Extra']."\t".
+						basename($backtrace[1]["file"])."\t".
+						$backtrace[1]["line"]."\t".$backtrace[2]["function"]."\t".
+						substr($query, 0, 2000)."\n", FILE_APPEND);
+			}
+		}
+	}
+
+	public static function escape($str) {
+		switch (self::$driver) {
+			case 'pdo':
+				return substr(@self::$db->quote($str, PDO::PARAM_STR), 1, -1);
+			case 'mysqli':
+				return @self::$db->real_escape_string($str);
+		}
+	}
+
+	public static function connected() {
+		$connected = false;
+
+		if (is_null(self::$db)) {
+			return false;
+		}
+
+		switch (self::$driver) {
+			case 'pdo':
+				$r = self::p("SELECT 1");
+				if (DBM::is_result($r)) {
+					$row = self::inArray($r);
+					$connected = ($row[0]['1'] == '1');
+				}
+				break;
+			case 'mysqli':
+				$connected = self::$db->ping();
+				break;
+		}
+		return $connected;
+	}
+
+	/**
+	 * @brief Replaces ANY_VALUE() function by MIN() function,
+	 *  if the database server does not support ANY_VALUE().
+	 *
+	 * Considerations for Standard SQL, or MySQL with ONLY_FULL_GROUP_BY (default since 5.7.5).
+	 * ANY_VALUE() is available from MySQL 5.7.5 https://dev.mysql.com/doc/refman/5.7/en/miscellaneous-functions.html
+	 * A standard fall-back is to use MIN().
+	 *
+	 * @param string $sql An SQL string without the values
+	 * @return string The input SQL string modified if necessary.
+	 */
+	public static function any_value_fallback($sql) {
+		$server_info = self::server_info();
+		if (version_compare($server_info, '5.7.5', '<') ||
+			(stripos($server_info, 'MariaDB') !== false)) {
+			$sql = str_ireplace('ANY_VALUE(', 'MIN(', $sql);
+		}
+		return $sql;
+	}
+
+	/**
+	 * @brief beautifies the query - useful for "SHOW PROCESSLIST"
+	 *
+	 * This is safe when we bind the parameters later.
+	 * The parameter values aren't part of the SQL.
+	 *
+	 * @param string $sql An SQL string without the values
+	 * @return string The input SQL string modified if necessary.
+	 */
+	public static function clean_query($sql) {
+		$search = ["\t", "\n", "\r", "  "];
+		$replace = [' ', ' ', ' ', ' '];
+		do {
+			$oldsql = $sql;
+			$sql = str_replace($search, $replace, $sql);
+		} while ($oldsql != $sql);
+
+		return $sql;
+	}
+
+
+	/**
+	 * @brief Replaces the ? placeholders with the parameters in the $args array
+	 *
+	 * @param string $sql SQL query
+	 * @param array $args The parameters that are to replace the ? placeholders
+	 * @return string The replaced SQL query
+	 */
+	private static function replaceParameters($sql, $args) {
+		$offset = 0;
+		foreach ($args AS $param => $value) {
+			if (is_int($args[$param]) || is_float($args[$param])) {
+				$replace = intval($args[$param]);
+			} else {
+				$replace = "'".self::escape($args[$param])."'";
+			}
+
+			$pos = strpos($sql, '?', $offset);
+			if ($pos !== false) {
+				$sql = substr_replace($sql, $replace, $pos, 1);
+			}
+			$offset = $pos + strlen($replace);
+		}
+		return $sql;
+	}
+
+	/**
+	 * @brief Convert parameter array to an universal form
+	 * @param array $args Parameter array
+	 * @return array universalized parameter array
+	 */
+	private static function getParam($args) {
+		unset($args[0]);
+
+		// When the second function parameter is an array then use this as the parameter array
+		if ((count($args) > 0) && (is_array($args[1]))) {
+			return $args[1];
+		} else {
+			return $args;
+		}
+	}
+
+	/**
+	 * @brief Executes a prepared statement that returns data
+	 * @usage Example: $r = p("SELECT * FROM `item` WHERE `guid` = ?", $guid);
+	 *
+	 * Please only use it with complicated queries.
+	 * For all regular queries please use dba::select or dba::exists
+	 *
+	 * @param string $sql SQL statement
+	 * @return bool|object statement object or result object
+	 */
+	public static function p($sql) {
+		$a = get_app();
+
+		$stamp1 = microtime(true);
+
+		$params = self::getParam(func_get_args());
+
+		// Renumber the array keys to be sure that they fit
+		$i = 0;
+		$args = [];
+		foreach ($params AS $param) {
+			// Avoid problems with some MySQL servers and boolean values. See issue #3645
+			if (is_bool($param)) {
+				$param = (int)$param;
+			}
+			$args[++$i] = $param;
+		}
+
+		if (!self::$connected) {
+			return false;
+		}
+
+		if ((substr_count($sql, '?') != count($args)) && (count($args) > 0)) {
+			// Question: Should we continue or stop the query here?
+			logger('Parameter mismatch. Query "'.$sql.'" - Parameters '.print_r($args, true), LOGGER_DEBUG);
+		}
+
+		$sql = self::clean_query($sql);
+		$sql = self::any_value_fallback($sql);
+
+		$orig_sql = $sql;
+
+		if ($a->getConfigValue('system', 'db_callstack')) {
+			$sql = "/*".System::callstack()." */ ".$sql;
+		}
+
+		self::$error = '';
+		self::$errorno = 0;
+		self::$affected_rows = 0;
+
+		// We have to make some things different if this function is called from "e"
+		$trace = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 2);
+
+		if (isset($trace[1])) {
+			$called_from = $trace[1];
+		} else {
+			// We use just something that is defined to avoid warnings
+			$called_from = $trace[0];
+		}
+		// We are having an own error logging in the function "e"
+		$called_from_e = ($called_from['function'] == 'e');
+
+		switch (self::$driver) {
+			case 'pdo':
+				// If there are no arguments we use "query"
+				if (count($args) == 0) {
+					if (!$retval = self::$db->query($sql)) {
+						$errorInfo = self::$db->errorInfo();
+						self::$error = $errorInfo[2];
+						self::$errorno = $errorInfo[1];
+						$retval = false;
+						break;
+					}
+					self::$affected_rows = $retval->rowCount();
+					break;
+				}
+
+				if (!$stmt = self::$db->prepare($sql)) {
+					$errorInfo = self::$db->errorInfo();
+					self::$error = $errorInfo[2];
+					self::$errorno = $errorInfo[1];
+					$retval = false;
+					break;
+				}
+
+				foreach ($args AS $param => $value) {
+					if (is_int($args[$param])) {
+						$data_type = PDO::PARAM_INT;
+					} else {
+						$data_type = PDO::PARAM_STR;
+					}
+					$stmt->bindParam($param, $args[$param], $data_type);
+				}
+
+				if (!$stmt->execute()) {
+					$errorInfo = $stmt->errorInfo();
+					self::$error = $errorInfo[2];
+					self::$errorno = $errorInfo[1];
+					$retval = false;
+				} else {
+					$retval = $stmt;
+					self::$affected_rows = $retval->rowCount();
+				}
+				break;
+			case 'mysqli':
+				// There are SQL statements that cannot be executed with a prepared statement
+				$parts = explode(' ', $orig_sql);
+				$command = strtolower($parts[0]);
+				$can_be_prepared = in_array($command, ['select', 'update', 'insert', 'delete']);
+
+				// The fallback routine is called as well when there are no arguments
+				if (!$can_be_prepared || (count($args) == 0)) {
+					$retval = self::$db->query(self::replaceParameters($sql, $args));
+					if (self::$db->errno) {
+						self::$error = self::$db->error;
+						self::$errorno = self::$db->errno;
+						$retval = false;
+					} else {
+						if (isset($retval->num_rows)) {
+							self::$affected_rows = $retval->num_rows;
+						} else {
+							self::$affected_rows = self::$db->affected_rows;
+						}
+					}
+					break;
+				}
+
+				$stmt = self::$db->stmt_init();
+
+				if (!$stmt->prepare($sql)) {
+					self::$error = $stmt->error;
+					self::$errorno = $stmt->errno;
+					$retval = false;
+					break;
+				}
+
+				$param_types = '';
+				$values = [];
+				foreach ($args AS $param => $value) {
+					if (is_int($args[$param])) {
+						$param_types .= 'i';
+					} elseif (is_float($args[$param])) {
+						$param_types .= 'd';
+					} elseif (is_string($args[$param])) {
+						$param_types .= 's';
+					} else {
+						$param_types .= 'b';
+					}
+					$values[] = &$args[$param];
+				}
+
+				if (count($values) > 0) {
+					array_unshift($values, $param_types);
+					call_user_func_array([$stmt, 'bind_param'], $values);
+				}
+
+				if (!$stmt->execute()) {
+					self::$error = self::$db->error;
+					self::$errorno = self::$db->errno;
+					$retval = false;
+				} else {
+					$stmt->store_result();
+					$retval = $stmt;
+					self::$affected_rows = $retval->affected_rows;
+				}
+				break;
+		}
+
+		// We are having an own error logging in the function "e"
+		if ((self::$errorno != 0) && !$called_from_e) {
+			// We have to preserve the error code, somewhere in the logging it get lost
+			$error = self::$error;
+			$errorno = self::$errorno;
+
+			logger('DB Error '.self::$errorno.': '.self::$error."\n".
+				System::callstack(8)."\n".self::replaceParameters($sql, $args));
+
+			// On a lost connection we try to reconnect - but only once.
+			if ($errorno == 2006) {
+				if (self::$in_retrial || !self::reconnect()) {
+					// It doesn't make sense to continue when the database connection was lost
+					if (self::$in_retrial) {
+						logger('Giving up retrial because of database error '.$errorno.': '.$error);
+					} else {
+						logger("Couldn't reconnect after database error ".$errorno.': '.$error);
+					}
+					exit(1);
+				} else {
+					// We try it again
+					logger('Reconnected after database error '.$errorno.': '.$error);
+					self::$in_retrial = true;
+					$ret = self::p($sql, $args);
+					self::$in_retrial = false;
+					return $ret;
+				}
+			}
+
+			self::$error = $error;
+			self::$errorno = $errorno;
+		}
+
+		$a->save_timestamp($stamp1, 'database');
+
+		if ($a->getConfigValue('system', 'db_log')) {
+			$stamp2 = microtime(true);
+			$duration = (float)($stamp2 - $stamp1);
+
+			if (($duration > $a->getConfigValue('system', 'db_loglimit'))) {
+				$duration = round($duration, 3);
+				$backtrace = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);
+
+				@file_put_contents($a->getConfigValue('system', 'db_log'), DateTimeFormat::utcNow()."\t".$duration."\t".
+						basename($backtrace[1]["file"])."\t".
+						$backtrace[1]["line"]."\t".$backtrace[2]["function"]."\t".
+						substr(self::replaceParameters($sql, $args), 0, 2000)."\n", FILE_APPEND);
+			}
+		}
+		return $retval;
+	}
+
+	/**
+	 * @brief Executes a prepared statement like UPDATE or INSERT that doesn't return data
+	 *
+	 * Please use dba::delete, dba::insert, dba::update, ... instead
+	 *
+	 * @param string $sql SQL statement
+	 * @return boolean Was the query successfull? False is returned only if an error occurred
+	 */
+	public static function e($sql) {
+		$a = get_app();
+
+		$stamp = microtime(true);
+
+		$params = self::getParam(func_get_args());
+
+		// In a case of a deadlock we are repeating the query 20 times
+		$timeout = 20;
+
+		do {
+			$stmt = self::p($sql, $params);
+
+			if (is_bool($stmt)) {
+				$retval = $stmt;
+			} elseif (is_object($stmt)) {
+				$retval = true;
+			} else {
+				$retval = false;
+			}
+
+			self::close($stmt);
+
+		} while ((self::$errorno == 1213) && (--$timeout > 0));
+
+		if (self::$errorno != 0) {
+			// We have to preserve the error code, somewhere in the logging it get lost
+			$error = self::$error;
+			$errorno = self::$errorno;
+
+			logger('DB Error '.self::$errorno.': '.self::$error."\n".
+				System::callstack(8)."\n".self::replaceParameters($sql, $params));
+
+			// On a lost connection we simply quit.
+			// A reconnect like in self::p could be dangerous with modifications
+			if ($errorno == 2006) {
+				logger('Giving up because of database error '.$errorno.': '.$error);
+				exit(1);
+			}
+
+			self::$error = $error;
+			self::$errorno = $errorno;
+		}
+
+		$a->save_timestamp($stamp, "database_write");
+
+		return $retval;
+	}
+
+	/**
+	 * @brief Check if data exists
+	 *
+	 * @param string $table Table name
+	 * @param array $condition array of fields for condition
+	 *
+	 * @return boolean Are there rows for that condition?
+	 */
+	public static function exists($table, $condition) {
+		if (empty($table)) {
+			return false;
+		}
+
+		$fields = [];
+
+		reset($condition);
+		$first_key = key($condition);
+		if (!is_int($first_key)) {
+			$fields = [$first_key];
+		}
+
+		$stmt = self::select($table, $fields, $condition, ['limit' => 1]);
+
+		if (is_bool($stmt)) {
+			$retval = $stmt;
+		} else {
+			$retval = (self::num_rows($stmt) > 0);
+		}
+
+		self::close($stmt);
+
+		return $retval;
+	}
+
+	/**
+	 * Fetches the first row
+	 *
+	 * Please use dba::selectFirst or dba::exists whenever this is possible.
+	 *
+	 * @brief Fetches the first row
+	 * @param string $sql SQL statement
+	 * @return array first row of query
+	 */
+	public static function fetch_first($sql) {
+		$params = self::getParam(func_get_args());
+
+		$stmt = self::p($sql, $params);
+
+		if (is_bool($stmt)) {
+			$retval = $stmt;
+		} else {
+			$retval = self::fetch($stmt);
+		}
+
+		self::close($stmt);
+
+		return $retval;
+	}
+
+	/**
+	 * @brief Returns the number of affected rows of the last statement
+	 *
+	 * @return int Number of rows
+	 */
+	public static function affected_rows() {
+		return self::$affected_rows;
+	}
+
+	/**
+	 * @brief Returns the number of columns of a statement
+	 *
+	 * @param object Statement object
+	 * @return int Number of columns
+	 */
+	public static function columnCount($stmt) {
+		if (!is_object($stmt)) {
+			return 0;
+		}
+		switch (self::$driver) {
+			case 'pdo':
+				return $stmt->columnCount();
+			case 'mysqli':
+				return $stmt->field_count;
+		}
+		return 0;
+	}
+	/**
+	 * @brief Returns the number of rows of a statement
+	 *
+	 * @param PDOStatement|mysqli_result|mysqli_stmt Statement object
+	 * @return int Number of rows
+	 */
+	public static function num_rows($stmt) {
+		if (!is_object($stmt)) {
+			return 0;
+		}
+		switch (self::$driver) {
+			case 'pdo':
+				return $stmt->rowCount();
+			case 'mysqli':
+				return $stmt->num_rows;
+		}
+		return 0;
+	}
+
+	/**
+	 * @brief Fetch a single row
+	 *
+	 * @param mixed $stmt statement object
+	 * @return array current row
+	 */
+	public static function fetch($stmt) {
+		$a = get_app();
+
+		$stamp1 = microtime(true);
+
+		$columns = [];
+
+		if (!is_object($stmt)) {
+			return false;
+		}
+
+		switch (self::$driver) {
+			case 'pdo':
+				$columns = $stmt->fetch(PDO::FETCH_ASSOC);
+				break;
+			case 'mysqli':
+				if (get_class($stmt) == 'mysqli_result') {
+					$columns = $stmt->fetch_assoc();
+					break;
+				}
+
+				// This code works, but is slow
+
+				// Bind the result to a result array
+				$cols = [];
+
+				$cols_num = [];
+				for ($x = 0; $x < $stmt->field_count; $x++) {
+					$cols[] = &$cols_num[$x];
+				}
+
+				call_user_func_array([$stmt, 'bind_result'], $cols);
+
+				if (!$stmt->fetch()) {
+					return false;
+				}
+
+				// The slow part:
+				// We need to get the field names for the array keys
+				// It seems that there is no better way to do this.
+				$result = $stmt->result_metadata();
+				$fields = $result->fetch_fields();
+
+				foreach ($cols_num AS $param => $col) {
+					$columns[$fields[$param]->name] = $col;
+				}
+		}
+
+		$a->save_timestamp($stamp1, 'database');
+
+		return $columns;
+	}
+
+	/**
+	 * @brief Insert a row into a table
+	 *
+	 * @param string $table Table name
+	 * @param array $param parameter array
+	 * @param bool $on_duplicate_update Do an update on a duplicate entry
+	 *
+	 * @return boolean was the insert successfull?
+	 */
+	public static function insert($table, $param, $on_duplicate_update = false) {
+
+		if (empty($table) || empty($param)) {
+			logger('Table and fields have to be set');
+			return false;
+		}
+
+		$sql = "INSERT INTO `".self::escape($table)."` (`".implode("`, `", array_keys($param))."`) VALUES (".
+			substr(str_repeat("?, ", count($param)), 0, -2).")";
+
+		if ($on_duplicate_update) {
+			$sql .= " ON DUPLICATE KEY UPDATE `".implode("` = ?, `", array_keys($param))."` = ?";
+
+			$values = array_values($param);
+			$param = array_merge_recursive($values, $values);
+		}
+
+		return self::e($sql, $param);
+	}
+
+	/**
+	 * @brief Fetch the id of the last insert command
+	 *
+	 * @return integer Last inserted id
+	 */
+	public static function lastInsertId() {
+		switch (self::$driver) {
+			case 'pdo':
+				$id = self::$db->lastInsertId();
+				break;
+			case 'mysqli':
+				$id = self::$db->insert_id;
+				break;
+		}
+		return $id;
+	}
+
+	/**
+	 * @brief Locks a table for exclusive write access
+	 *
+	 * This function can be extended in the future to accept a table array as well.
+	 *
+	 * @param string $table Table name
+	 *
+	 * @return boolean was the lock successful?
+	 */
+	public static function lock($table) {
+		// See here: https://dev.mysql.com/doc/refman/5.7/en/lock-tables-and-transactions.html
+		if (self::$driver == 'pdo') {
+			self::e("SET autocommit=0");
+			self::$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, true);
+		} else {
+			self::$db->autocommit(false);
+		}
+
+		$success = self::e("LOCK TABLES `".self::escape($table)."` WRITE");
+
+		if (self::$driver == 'pdo') {
+			self::$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
+		}
+
+		if (!$success) {
+			if (self::$driver == 'pdo') {
+				self::e("SET autocommit=1");
+			} else {
+				self::$db->autocommit(true);
+			}
+		} else {
+			self::$in_transaction = true;
+		}
+		return $success;
+	}
+
+	/**
+	 * @brief Unlocks all locked tables
+	 *
+	 * @return boolean was the unlock successful?
+	 */
+	public static function unlock() {
+		// See here: https://dev.mysql.com/doc/refman/5.7/en/lock-tables-and-transactions.html
+		self::performCommit();
+
+		if (self::$driver == 'pdo') {
+			self::$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, true);
+		}
+
+		$success = self::e("UNLOCK TABLES");
+
+		if (self::$driver == 'pdo') {
+			self::$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
+			self::e("SET autocommit=1");
+		} else {
+			self::$db->autocommit(true);
+		}
+
+		self::$in_transaction = false;
+		return $success;
+	}
+
+	/**
+	 * @brief Starts a transaction
+	 *
+	 * @return boolean Was the command executed successfully?
+	 */
+	public static function transaction() {
+		if (!self::performCommit()) {
+			return false;
+		}
+
+		switch (self::$driver) {
+			case 'pdo':
+				if (self::$db->inTransaction()) {
+					break;
+				}
+				if (!self::$db->beginTransaction()) {
+					return false;
+				}
+				break;
+			case 'mysqli':
+				if (!self::$db->begin_transaction()) {
+					return false;
+				}
+				break;
+		}
+
+		self::$in_transaction = true;
+		return true;
+	}
+
+	private static function performCommit()
+	{
+		switch (self::$driver) {
+			case 'pdo':
+				if (!self::$db->inTransaction()) {
+					return true;
+				}
+				return self::$db->commit();
+			case 'mysqli':
+				return self::$db->commit();
+		}
+		return true;
+	}
+
+	/**
+	 * @brief Does a commit
+	 *
+	 * @return boolean Was the command executed successfully?
+	 */
+	public static function commit() {
+		if (!self::performCommit()) {
+			return false;
+		}
+		self::$in_transaction = false;
+		return true;
+	}
+
+	/**
+	 * @brief Does a rollback
+	 *
+	 * @return boolean Was the command executed successfully?
+	 */
+	public static function rollback() {
+		$ret = false;
+
+		switch (self::$driver) {
+			case 'pdo':
+				if (!self::$db->inTransaction()) {
+					$ret = true;
+					break;
+				}
+				$ret = self::$db->rollBack();
+				break;
+			case 'mysqli':
+				$ret = self::$db->rollback();
+				break;
+		}
+		self::$in_transaction = false;
+		return $ret;
+	}
+
+	/**
+	 * @brief Build the array with the table relations
+	 *
+	 * The array is build from the database definitions in DBStructure.php
+	 *
+	 * This process must only be started once, since the value is cached.
+	 */
+	private static function buildRelationData() {
+		$definition = DBStructure::definition();
+
+		foreach ($definition AS $table => $structure) {
+			foreach ($structure['fields'] AS $field => $field_struct) {
+				if (isset($field_struct['relation'])) {
+					foreach ($field_struct['relation'] AS $rel_table => $rel_field) {
+						self::$relation[$rel_table][$rel_field][$table][] = $field;
+					}
+				}
+			}
+		}
+	}
+
+	/**
+	 * @brief Delete a row from a table
+	 *
+	 * @param string  $table       Table name
+	 * @param array   $conditions  Field condition(s)
+	 * @param array   $options
+	 *                - cascade: If true we delete records in other tables that depend on the one we're deleting through
+	 *                           relations (default: true)
+	 * @param boolean $in_process  Internal use: Only do a commit after the last delete
+	 * @param array   $callstack   Internal use: prevent endless loops
+	 *
+	 * @return boolean|array was the delete successful? When $in_process is set: deletion data
+	 */
+	public static function delete($table, array $conditions, array $options = [], $in_process = false, array &$callstack = [])
+	{
+		if (empty($table) || empty($conditions)) {
+			logger('Table and conditions have to be set');
+			return false;
+		}
+
+		$commands = [];
+
+		// Create a key for the loop prevention
+		$key = $table . ':' . json_encode($conditions);
+
+		// We quit when this key already exists in the callstack.
+		if (isset($callstack[$key])) {
+			return $commands;
+		}
+
+		$callstack[$key] = true;
+
+		$table = self::escape($table);
+
+		$commands[$key] = ['table' => $table, 'conditions' => $conditions];
+
+		$cascade = defaults($options, 'cascade', true);
+
+		// To speed up the whole process we cache the table relations
+		if ($cascade && count(self::$relation) == 0) {
+			self::buildRelationData();
+		}
+
+		// Is there a relation entry for the table?
+		if ($cascade && isset(self::$relation[$table])) {
+			// We only allow a simple "one field" relation.
+			$field = array_keys(self::$relation[$table])[0];
+			$rel_def = array_values(self::$relation[$table])[0];
+
+			// Create a key for preventing double queries
+			$qkey = $field . '-' . $table . ':' . json_encode($conditions);
+
+			// When the search field is the relation field, we don't need to fetch the rows
+			// This is useful when the leading record is already deleted in the frontend but the rest is done in the backend
+			if ((count($conditions) == 1) && ($field == array_keys($conditions)[0])) {
+				foreach ($rel_def AS $rel_table => $rel_fields) {
+					foreach ($rel_fields AS $rel_field) {
+						$retval = self::delete($rel_table, [$rel_field => array_values($conditions)[0]], $options, true, $callstack);
+						$commands = array_merge($commands, $retval);
+					}
+				}
+				// We quit when this key already exists in the callstack.
+			} elseif (!isset($callstack[$qkey])) {
+
+				$callstack[$qkey] = true;
+
+				// Fetch all rows that are to be deleted
+				$data = self::select($table, [$field], $conditions);
+
+				while ($row = self::fetch($data)) {
+					// Now we accumulate the delete commands
+					$retval = self::delete($table, [$field => $row[$field]], $options, true, $callstack);
+					$commands = array_merge($commands, $retval);
+				}
+
+				self::close($data);
+
+				// Since we had split the delete command we don't need the original command anymore
+				unset($commands[$key]);
+			}
+		}
+
+		if (!$in_process) {
+			// Now we finalize the process
+			$do_transaction = !self::$in_transaction;
+
+			if ($do_transaction) {
+				self::transaction();
+			}
+
+			$compacted = [];
+			$counter = [];
+
+			foreach ($commands AS $command) {
+				$conditions = $command['conditions'];
+				reset($conditions);
+				$first_key = key($conditions);
+
+				$condition_string = self::buildCondition($conditions);
+
+				if ((count($command['conditions']) > 1) || is_int($first_key)) {
+					$sql = "DELETE FROM `" . $command['table'] . "`" . $condition_string;
+					logger(self::replaceParameters($sql, $conditions), LOGGER_DATA);
+
+					if (!self::e($sql, $conditions)) {
+						if ($do_transaction) {
+							self::rollback();
+						}
+						return false;
+					}
+				} else {
+					$key_table = $command['table'];
+					$key_condition = array_keys($command['conditions'])[0];
+					$value = array_values($command['conditions'])[0];
+
+					// Split the SQL queries in chunks of 100 values
+					// We do the $i stuff here to make the code better readable
+					$i = isset($counter[$key_table][$key_condition]) ? $counter[$key_table][$key_condition] : 0;
+					if (isset($compacted[$key_table][$key_condition][$i]) && count($compacted[$key_table][$key_condition][$i]) > 100) {
+						++$i;
+					}
+
+					$compacted[$key_table][$key_condition][$i][$value] = $value;
+					$counter[$key_table][$key_condition] = $i;
+				}
+			}
+			foreach ($compacted AS $table => $values) {
+				foreach ($values AS $field => $field_value_list) {
+					foreach ($field_value_list AS $field_values) {
+						$sql = "DELETE FROM `" . $table . "` WHERE `" . $field . "` IN (" .
+							substr(str_repeat("?, ", count($field_values)), 0, -2) . ");";
+
+						logger(self::replaceParameters($sql, $field_values), LOGGER_DATA);
+
+						if (!self::e($sql, $field_values)) {
+							if ($do_transaction) {
+								self::rollback();
+							}
+							return false;
+						}
+					}
+				}
+			}
+			if ($do_transaction) {
+				self::commit();
+			}
+			return true;
+		}
+
+		return $commands;
+	}
+
+	/**
+	 * @brief Updates rows
+	 *
+	 * Updates rows in the database. When $old_fields is set to an array,
+	 * the system will only do an update if the fields in that array changed.
+	 *
+	 * Attention:
+	 * Only the values in $old_fields are compared.
+	 * This is an intentional behaviour.
+	 *
+	 * Example:
+	 * We include the timestamp field in $fields but not in $old_fields.
+	 * Then the row will only get the new timestamp when the other fields had changed.
+	 *
+	 * When $old_fields is set to a boolean value the system will do this compare itself.
+	 * When $old_fields is set to "true" the system will do an insert if the row doesn't exists.
+	 *
+	 * Attention:
+	 * Only set $old_fields to a boolean value when you are sure that you will update a single row.
+	 * When you set $old_fields to "true" then $fields must contain all relevant fields!
+	 *
+	 * @param string $table Table name
+	 * @param array $fields contains the fields that are updated
+	 * @param array $condition condition array with the key values
+	 * @param array|boolean $old_fields array with the old field values that are about to be replaced (true = update on duplicate)
+	 *
+	 * @return boolean was the update successfull?
+	 */
+	public static function update($table, $fields, $condition, $old_fields = []) {
+
+		if (empty($table) || empty($fields) || empty($condition)) {
+			logger('Table, fields and condition have to be set');
+			return false;
+		}
+
+		$table = self::escape($table);
+
+		$condition_string = self::buildCondition($condition);
+
+		if (is_bool($old_fields)) {
+			$do_insert = $old_fields;
+
+			$old_fields = self::selectFirst($table, [], $condition);
+
+			if (is_bool($old_fields)) {
+				if ($do_insert) {
+					$values = array_merge($condition, $fields);
+					return self::insert($table, $values, $do_insert);
+				}
+				$old_fields = [];
+			}
+		}
+
+		$do_update = (count($old_fields) == 0);
+
+		foreach ($old_fields AS $fieldname => $content) {
+			if (isset($fields[$fieldname])) {
+				if ($fields[$fieldname] == $content) {
+					unset($fields[$fieldname]);
+				} else {
+					$do_update = true;
+				}
+			}
+		}
+
+		if (!$do_update || (count($fields) == 0)) {
+			return true;
+		}
+
+		$sql = "UPDATE `".$table."` SET `".
+			implode("` = ?, `", array_keys($fields))."` = ?".$condition_string;
+
+		$params1 = array_values($fields);
+		$params2 = array_values($condition);
+		$params = array_merge_recursive($params1, $params2);
+
+		return self::e($sql, $params);
+	}
+
+	/**
+	 * Retrieve a single record from a table and returns it in an associative array
+	 *
+	 * @brief Retrieve a single record from a table
+	 * @param string $table
+	 * @param array  $fields
+	 * @param array  $condition
+	 * @param array  $params
+	 * @return bool|array
+	 * @see self::select
+	 */
+	public static function selectFirst($table, array $fields = [], array $condition = [], $params = [])
+	{
+		$params['limit'] = 1;
+		$result = self::select($table, $fields, $condition, $params);
+
+		if (is_bool($result)) {
+			return $result;
+		} else {
+			$row = self::fetch($result);
+			self::close($result);
+			return $row;
+		}
+	}
+
+	/**
+	 * @brief Select rows from a table
+	 *
+	 * @param string $table     Table name
+	 * @param array  $fields    Array of selected fields, empty for all
+	 * @param array  $condition Array of fields for condition
+	 * @param array  $params    Array of several parameters
+	 *
+	 * @return boolean|object
+	 *
+	 * Example:
+	 * $table = "item";
+	 * $fields = array("id", "uri", "uid", "network");
+	 *
+	 * $condition = array("uid" => 1, "network" => 'dspr');
+	 * or:
+	 * $condition = array("`uid` = ? AND `network` IN (?, ?)", 1, 'dfrn', 'dspr');
+	 *
+	 * $params = array("order" => array("id", "received" => true), "limit" => 10);
+	 *
+	 * $data = dba::select($table, $fields, $condition, $params);
+	 */
+	public static function select($table, array $fields = [], array $condition = [], array $params = [])
+	{
+		if ($table == '') {
+			return false;
+		}
+
+		$table = self::escape($table);
+
+		if (count($fields) > 0) {
+			$select_fields = "`" . implode("`, `", array_values($fields)) . "`";
+		} else {
+			$select_fields = "*";
+		}
+
+		$condition_string = self::buildCondition($condition);
+
+		$param_string = self::buildParameter($params);
+
+		$sql = "SELECT " . $select_fields . " FROM `" . $table . "`" . $condition_string . $param_string;
+
+		$result = self::p($sql, $condition);
+
+		return $result;
+	}
+
+	/**
+	 * @brief Counts the rows from a table satisfying the provided condition
+	 *
+	 * @param string $table Table name
+	 * @param array $condition array of fields for condition
+	 *
+	 * @return int
+	 *
+	 * Example:
+	 * $table = "item";
+	 *
+	 * $condition = ["uid" => 1, "network" => 'dspr'];
+	 * or:
+	 * $condition = ["`uid` = ? AND `network` IN (?, ?)", 1, 'dfrn', 'dspr'];
+	 *
+	 * $count = dba::count($table, $condition);
+	 */
+	public static function count($table, array $condition = [])
+	{
+		if ($table == '') {
+			return false;
+		}
+
+		$condition_string = self::buildCondition($condition);
+
+		$sql = "SELECT COUNT(*) AS `count` FROM `".$table."`".$condition_string;
+
+		$row = self::fetch_first($sql, $condition);
+
+		return $row['count'];
+	}
+
+	/**
+	 * @brief Returns the SQL condition string built from the provided condition array
+	 *
+	 * This function operates with two modes.
+	 * - Supplied with a filed/value associative array, it builds simple strict
+	 *   equality conditions linked by AND.
+	 * - Supplied with a flat list, the first element is the condition string and
+	 *   the following arguments are the values to be interpolated
+	 *
+	 * $condition = ["uid" => 1, "network" => 'dspr'];
+	 * or:
+	 * $condition = ["`uid` = ? AND `network` IN (?, ?)", 1, 'dfrn', 'dspr'];
+	 *
+	 * In either case, the provided array is left with the parameters only
+	 *
+	 * @param array $condition
+	 * @return string
+	 */
+	public static function buildCondition(array &$condition = [])
+	{
+		$condition_string = '';
+		if (count($condition) > 0) {
+			reset($condition);
+			$first_key = key($condition);
+			if (is_int($first_key)) {
+				$condition_string = " WHERE (" . array_shift($condition) . ")";
+			} else {
+				$new_values = [];
+				$condition_string = "";
+				foreach ($condition as $field => $value) {
+					if ($condition_string != "") {
+						$condition_string .= " AND ";
+					}
+					if (is_array($value)) {
+						/* Workaround for MySQL Bug #64791.
+						 * Never mix data types inside any IN() condition.
+						 * In case of mixed types, cast all as string.
+						 * Logic needs to be consistent with dba::p() data types.
+						 */
+						$is_int = false;
+						$is_alpha = false;
+						foreach ($value as $single_value) {
+							if (is_int($single_value)) {
+								$is_int = true;
+							} else {
+								$is_alpha = true;
+							}
+						}
+
+						if ($is_int && $is_alpha) {
+							foreach ($value as &$ref) {
+								if (is_int($ref)) {
+									$ref = (string)$ref;
+								}
+							}
+							unset($ref); //Prevent accidental re-use.
+						}
+
+						$new_values = array_merge($new_values, array_values($value));
+						$placeholders = substr(str_repeat("?, ", count($value)), 0, -2);
+						$condition_string .= "`" . $field . "` IN (" . $placeholders . ")";
+					} else {
+						$new_values[$field] = $value;
+						$condition_string .= "`" . $field . "` = ?";
+					}
+				}
+				$condition_string = " WHERE (" . $condition_string . ")";
+				$condition = $new_values;
+			}
+		}
+
+		return $condition_string;
+	}
+
+	/**
+	 * @brief Returns the SQL parameter string built from the provided parameter array
+	 *
+	 * @param array $params
+	 * @return string
+	 */
+	public static function buildParameter(array $params = [])
+	{
+		$order_string = '';
+		if (isset($params['order'])) {
+			$order_string = " ORDER BY ";
+			foreach ($params['order'] AS $fields => $order) {
+				if (!is_int($fields)) {
+					$order_string .= "`" . $fields . "` " . ($order ? "DESC" : "ASC") . ", ";
+				} else {
+					$order_string .= "`" . $order . "`, ";
+				}
+			}
+			$order_string = substr($order_string, 0, -2);
+		}
+
+		$limit_string = '';
+		if (isset($params['limit']) && is_int($params['limit'])) {
+			$limit_string = " LIMIT " . $params['limit'];
+		}
+
+		if (isset($params['limit']) && is_array($params['limit'])) {
+			$limit_string = " LIMIT " . intval($params['limit'][0]) . ", " . intval($params['limit'][1]);
+		}
+
+		return $order_string.$limit_string;
+	}
+
+	/**
+	 * @brief Fills an array with data from a query
+	 *
+	 * @param object $stmt statement object
+	 * @return array Data array
+	 */
+	public static function inArray($stmt, $do_close = true) {
+		if (is_bool($stmt)) {
+			return $stmt;
+		}
+
+		$data = [];
+		while ($row = self::fetch($stmt)) {
+			$data[] = $row;
+		}
+		if ($do_close) {
+			self::close($stmt);
+		}
+		return $data;
+	}
+
+	/**
+	 * @brief Returns the error number of the last query
+	 *
+	 * @return string Error number (0 if no error)
+	 */
+	public static function errorNo() {
+		return self::$errorno;
+	}
+
+	/**
+	 * @brief Returns the error message of the last query
+	 *
+	 * @return string Error message ('' if no error)
+	 */
+	public static function errorMessage() {
+		return self::$error;
+	}
+
+	/**
+	 * @brief Closes the current statement
+	 *
+	 * @param object $stmt statement object
+	 * @return boolean was the close successful?
+	 */
+	public static function close($stmt) {
+		$a = get_app();
+
+		$stamp1 = microtime(true);
+
+		if (!is_object($stmt)) {
+			return false;
+		}
+
+		switch (self::$driver) {
+			case 'pdo':
+				$ret = $stmt->closeCursor();
+				break;
+			case 'mysqli':
+				// MySQLi offers both a mysqli_stmt and a mysqli_result class.
+				// We should be careful not to assume the object type of $stmt
+				// because dba::p() has been able to return both types.
+				if ($stmt instanceof mysqli_stmt) {
+					$stmt->free_result();
+					$ret = $stmt->close();
+				} elseif ($stmt instanceof mysqli_result) {
+					$stmt->free();
+					$ret = true;
+				} else {
+					$ret = false;
+				}
+				break;
+		}
+
+		$a->save_timestamp($stamp1, 'database');
+
+		return $ret;
+	}
+}