When the MySQL server has "gone away," attempt to reconnect and retry the query.

props pento.
see #5932.


git-svn-id: https://develop.svn.wordpress.org/trunk@27075 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/wp-db.php

@@ -157,6 +157,16 @@ class wpdb {
 	 */
 	var $queries;
 
+	/**
+	 * The number of times to retry reconnecting before dying.
+	 *
+	 * @since 3.9.0
+	 * @access protected
+	 * @see wpdb::check_connection()
+	 * @var int
+	 */
+	protected $reconnect_retries = 5;
+
 	/**
 	 * WordPress table prefix
 	 *
@@ -1192,11 +1202,17 @@ class wpdb {
 	}
 
 	/**
-	 * Connect to and select database
+	 * Connect to and select database.
 	 *
 	 * @since 3.0.0
+	 *
+	 * @param bool $allow_bail Optional. Allows the function to bail, default true. If this is set
+	 *                         to false, you will need to handle the lack of database connection
+	 *                         manually. Available since 3.9.0.
+	 *
+	 * @return bool True with a successful connection, false on failure.
 	 */
-	function db_connect() {
+	function db_connect( $allow_bail = true ) {
 
 		$this->is_mysql = true;
 
@@ -1217,7 +1233,7 @@ class wpdb {
 			$this->dbh = @mysql_connect( $this->dbhost, $this->dbuser, $this->dbpassword, $new_link, $client_flags );
 		}
 
-		if ( !$this->dbh ) {
+		if ( ! $this->dbh && $allow_bail ) {
 			wp_load_translations_early();
 
 			// Load custom DB error template, if present.
@@ -1237,16 +1253,72 @@ class wpdb {
 <p>If you're unsure what these terms mean you should probably contact your host. If you still need help you can always visit the <a href='http://wordpress.org/support/'>WordPress Support Forums</a>.</p>
 " ), htmlspecialchars( $this->dbhost, ENT_QUOTES ) ), 'db_connect_fail' );
 
-			return;
+			return false;
+		} else if ( $this->dbh ) {
+			$this->set_charset( $this->dbh );
+			$this->set_sql_mode();
+			$this->ready = true;
+			$this->select( $this->dbname, $this->dbh );
+
+			return true;
 		}
 
-		$this->set_charset( $this->dbh );
+		return false;
+	}
 
-		$this->set_sql_mode();
+	/**
+	 * Check that the connection to the database is still up. If not, try to reconnect.
+	 *
+	 * If this function is unable to reconnect, it will forcibly die.
+	 *
+	 * @since 3.9.0
+	 *
+	 * @return bool True if the connection is up.
+	 */
+	function check_connection() {
+		if ( @mysql_ping( $this->dbh ) ) {
+			return true;
+		}
 
-		$this->ready = true;
+		$error_reporting = false;
 
-		$this->select( $this->dbname, $this->dbh );
+		// Disable warnings, as we don't want to see a multitude of "unable to connect" messages
+		if ( WP_DEBUG ) {
+			$error_reporting = error_reporting();
+			error_reporting( $error_reporting & ~E_WARNING );
+		}
+
+		for ( $tries = 1; $tries <= $this->reconnect_retries; $tries++ ) {
+			// On the last try, re-enable warnings. We want to see a single instance of the
+			// "unable to connect" message on the bail() screen, if it appears.
+			if ( $this->reconnect_retries === $tries && WP_DEBUG ) {
+				error_reporting( $error_reporting );
+			}
+
+			if ( $this->db_connect( false ) ) {
+				if ( $error_reporting ) {
+					error_reporting( $error_reporting );
+				}
+
+				return true;
+			}
+
+			sleep( 1 );
+		}
+
+		// We weren't able to reconnect, so we better bail.
+		$this->bail( sprintf( ( "
+<h1>Error reconnecting to the database</h1>
+<p>This means that we lost contact with the database server at <code>%s</code>. This could mean your host's database server is down.</p>
+<ul>
+	<li>Are you sure that the database server is running?</li>
+	<li>Are you sure that the database server is not under particularly heavy load?</li>
+</ul>
+<p>If you're unsure what these terms mean you should probably contact your host. If you still need help you can always visit the <a href='http://wordpress.org/support/'>WordPress Support Forums</a>.</p>
+" ), htmlspecialchars( $this->dbhost, ENT_QUOTES ) ), 'db_connect_fail' );
+
+		// Call dead_db() if bail didn't die, because this database is no more. It has ceased to be (at least temporarily).
+		dead_db();
 	}
 
 	/**
@@ -1262,6 +1334,7 @@ class wpdb {
 	function query( $query ) {
 		if ( ! $this->ready )
 			return false;
+
 		/**
 		 * Filter the database query.
 		 *
@@ -1281,14 +1354,14 @@ class wpdb {
 		// Keep track of the last query for debug..
 		$this->last_query = $query;
 
-		if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES )
+		$this->_do_query( $query );
-			$this->timer_start();
 
-		$this->result = @mysql_query( $query, $this->dbh );
+		// MySQL server has gone away, try to reconnect
-		$this->num_queries++;
+		if ( empty( $this->dbh ) || 2006 == mysql_errno( $this->dbh ) ) {
-
+			if ( $this->check_connection() ) {
-		if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES )
+				$this->_do_query( $query );
-			$this->queries[] = array( $query, $this->timer_stop(), $this->get_caller() );
+			}
+		}
 
 		// If there is an error then take note of it..
 		if ( $this->last_error = mysql_error( $this->dbh ) ) {
@@ -1326,6 +1399,29 @@ class wpdb {
 		return $return_val;
 	}
 
+	/**
+	 * Internal function to perform the mysql_query call
+	 *
+	 * @since 3.9.0
+	 *
+	 * @access private
+	 * @see wpdb::query()
+	 *
+	 * @param string $query The query to run
+	 */
+	private function _do_query( $query ) {
+		if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES ) {
+			$this->timer_start();
+		}
+
+		$this->result = @mysql_query( $query, $this->dbh );
+		$this->num_queries++;
+
+		if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES ) {
+			$this->queries[] = array( $query, $this->timer_stop(), $this->get_caller() );
+		}
+	}
+
 	/**
 	 * Insert a row into a table.
 	 *

tests/phpunit/tests/db.php

@@ -40,6 +40,23 @@ class Tests_DB extends WP_UnitTestCase {
 		return $sql;
 	}
 
+	/**
+	 * Test that WPDB will reconnect when the DB link dies
+	 * @ticket 5932
+	 */
+	public function test_db_reconnect() {
+		global $wpdb;
+
+		$var = $wpdb->get_var( "SELECT ID FROM $wpdb->users LIMIT 1" );
+		$this->assertGreaterThan( 0, $var );
+
+		mysql_close( $wpdb->dbh );
+		unset( $wpdb->dbh );
+
+		$var = $wpdb->get_var( "SELECT ID FROM $wpdb->users LIMIT 1" );
+		$this->assertGreaterThan( 0, $var );
+	}
+
 	/**
 	 * Test that floats formatted as "0,700" get sanitized properly by wpdb
 	 * @global mixed $wpdb