See Also consistent read, isolation level, non-repeatable read, READ UNCOMMITTED, REPEATABLE READ, SERIALIZABLE, transaction. PHP  A programming language originating with web applications. The code is typically embedded as blocks within the source of a web page, with the output substituted into the page as it is transmitted by the web server. This is in contrast to applications such as CGI scripts that print output in the form of an entire web page. The PHP style of coding is used for highly interactive and dynamic web pages. Modern PHP programs can also be run as command-line or GUI applications. MySQL applications are written using one of the  PHP APIs . Reusable modules can be written in  C  and called from PHP. Another technology for writing server-side web pages with MySQL is  ASP.net . See Also ASP.net, C, PHP API. PHP API  Several  APIs  are available for writing MySQL applications in the  PHP  language: the original MySQL API ( Mysql ) the MySQL Improved Extension ( Mysqli ) the MySQL Native Driver ( Mysqlnd ) the MySQL functions ( PDO_MYSQL ), and Connector/PHP. For details, see MySQL and PHP. See Also API, PHP. physical  A type of operation that involves hardware-related aspects such as disk blocks, memory pages, files, bits, disk reads, and so on. Typically, physical aspects are important during expert-level performance tuning and problem diagnosis. Contrast with  logical . See Also logical, physical backup. physical backup  A  backup  that copies the actual data files. For example, the  mysqlbackup  command of the  MySQL Enterprise Backup  product produces a physical backup, because its output contains data files that can be used directly by the  mysqld  server, resulting in a faster  restore  operation. Contrast with  logical backup . See Also backup, logical backup, MySQL Enterprise Backup, restore. PITR  Acronym for  point-in-time recovery . See Also point-in-time recovery. plan stability  A property of a  query execution plan , where the optimizer makes the same choices each time for a given query , so that performance is consistent and predictable. See Also query, query execution plan. point-in-time recovery  The process of restoring a  backup  to recreate the state of the database at a specific date and time. Commonly abbreviated “PITR” . Because it is unlikely that the specified time corresponds exactly to the time of a backup, this technique usually requires a combination of a  physical backup  and a  logical backup . For example, with the MySQL Enterprise Backup  product, you restore the last backup that you took before the specified point in time, then replay changes from the  binary log  between the time of the backup and the PITR time. See Also backup, binary log, logical backup, MySQL Enterprise Backup, physical backup. port  The number of the TCP/IP socket the database server listens on, used to establish a  connection . Often specified in conjunction with a  host . Depending on your use of network encryption, there might be one port for unencrypted traffic and another port for  SSL  connections. 6176