Over the last few weeks I had been quite silent, but that's about to change: Over the next few weeks I'll give a few presentations. Feel free to join any of those.

• January, 18th: Erstellung hochperformanter PHP-Anwendungen mit MySQL (German)
  MySQL Webinar, Online
• February, 9th: MySQL Konnectoren (German)
  OTN Developer Day: MySQL, Frankfurt, Germany
• February 24th/25th: PHP under the hood (English)
  PHP UK Conference, London, UK

One of the great things about the HTTP protocol, besides status code 418, is that it's stateless. A web server therefore is not required to store any information on the user or allocate resources for a user after the individual request is done. By that a single web server can handle many many many different users easily, and well if it can't anymore one can add a new server, put a simple load balancer in front and scale out. Each of those web servers then handles its requests without the need for communication which leads to linear scaling (assuming network provides enough bandwidth etc.).

Now the Web isn't used for serving static documents only anymore but we have all these fancy web apps. And those applications often have the need for a state. The most trivial information they need is the current user. HTTP is a great protocol and provides a way to do authentication which works well with its stateless nature - unfortunately this authentication is implemented badly in current clients. Ugly popups, no logout button, ... I don't have to tell more I think. For having nicer login systems people want web forms. Now the stateless nature of HTTP is a problem: The user may login and then browse around. On later requests it should still be known who that user is - with a custom HTML form based login alone this is not possible. A solution might be cookies. At least one might think so for a second. But setting a cookie "this is an authorized user" alone doesn't make sense as it could easily be faked. Better is to simply store a random identifier in a cookie and then keep a state information on the server. Then all session data is protected and only the user who knows this random identifier is authenticated. If this identifier is wisely chosen and hard to guess this works quite well. Luckily this is a mostly PHP- and MySQL-focused blog and as PHP is a system for building web applications this functionality is part of the core language: The PHP session module.

The session module, which was introduced in PHP 4, partly based on work on the famous phplib library, is quite a fascinating piece of code. It is open and extendable in so many directions but still so simple to use that everybody uses it, often newcomers learn about it on their first day in PHP land. Of course you can not only store the information whether the user is logged in but cache some user-specific data or keep the state on some transactions by the user, like multi-page forms or such.

In its default configuration session state will be stored on the web server's file system. Each session's data in its own file in serialized form. If the filesystem does some caching or one uses a ramdisk or something this can be quite efficient. But as we suddenly have a state on the web server we can't scale as easily as before anymore: If we add a new server and then route a user with an existing session to the new server all the session data won't be there. That is bad. This is often solved by a configuration of the load balancer to route all requests from the same user to the same web server. In some cases this works quite ok, but it is often seen that this might cause problems. Let's assume you want to take a machine down for maintenance. All sessions there will die. Or imagine there's a bunch of users who do complex and expensive tasks - then one of your servers will have a hard time, giving these users bad response times which feels like bad service, even though your other systems are mostly idle.

A nice solution for this would be to store the sessions in a central repository which can be accessed from all web servers.

For the last few months I had quite a few MySQL blog posts and didn't have anything from my "new features in PHP [trunk|5.4]" series. This article is a bridge between those two. The PHP 5.4 NEWS file has a small entry:

MySQLi: Added iterator support in MySQLi. mysqli_result implements Traversable. (Andrey, Johannes)

From the outside it is a really small change and easy to miss. The mentioned class, mysqli_result, implements an interface which adds no new methods. What once can't see is that this relates to some internal C-level functions which can be called by the engine for doing a foreach iteration on objects of this class. So with PHP 5.4 you don't have to use an "ugly" while construct anymore to fetch rows from a mysqli result but can simply do a foreach:

mysqli_report(MYSQLI_REPORT_STRICT);
try {
    $mysqli = new mysqli(/* ... */);
    foreach ($myslqi->query("SELECT a, b, c FROM t") as $row) {
        /* Process $row which is an associative array */
    }
} catch (mysqli_sql_exception $e) {
    /* an error happened ... */
}

I'm configuring mysqli in a way to throw exceptions on error. This is useful in this case as mysqli::query() might return false in the case of an error. Passing false to a foreach will give a fatal error, so I'd need a temporary variable and a check in front of the foreach loop, with exceptions I simply do the error handling in the catch block.

One thing to note is that mysqli is using buffered results ("store result") by default. If you want to use unbuffered result sets ("use result") you can easily do that by setting the flag accordingly:

foreach ($myslqi->query("SELECT a, b, c FROM t", MYSQLI_USE_RESULT) as $row) {
    /* ... */
}

People who are advanced with iterators in PHP might ask "Why did you implement Traversable only, not Iterator?" - the main reason is that we simply didn't want to. The mysqli_result class already has quite a few methods and we didn't want to make the interface confusing. If you need an Iterator class for some purpose you can simply wrap mysqli_result in an IteratoIterator.

Previously I was writing about combining Symfony2 and mysqlnd to get more statistics on what is going on below the surface in the database communication when using a Symfony2 application via the Symfony2 profiler. Now that's not all that can be done and I gave some ideas for extending this. One idea was adding mysqlnd_qc support. mysqlnd_qc is the client side query cache plugin for mysqlnd. This provides a client-side cache for query results transparently without changing the application.

A nice thing about this plugin, for this context here, is the function mysqlnd_qc_get_query_trace_log() which provides information about each query being executed. Not only the query string but also some timing (execution time, result storage time) and a stack trace so you can see where in the code a query was executed. I've added this functionality to the JSMysqlndBundle as you can see in the screenshot. I won't show a screenshot about what happens if you click the stacktrace link as this currently breaks the layout a bit, but maybe somebody wants to make this nicer? - Or maybe even feels motivated to make it even better using mysqlnd_uh (which, as of today, has docs, thanks to Ulf) Feel free to contact me to talk about ideas!

In a previous blog posting I was mentioning that I'm working on a small hobby PHP project. As I'm using this project to update myself to current frameworks I've decided to use Symfony2. Symfony provides a nice feature, which is the Symfony Profilier, an extensive logging and reporting system for Symfony2 developers to understand what's going on. A part of it is the Doctrine query logger which lists all database queries executed by Doctrine and their execution time.

This is nice but when we're using mysqlnd in our PHP build we have more information available. "So why not use that information," I thought and built a new bundle for Symfony2 doing exactly that. The JSMysqlndBundle will take all the 150 or so statistic values collected, so they can be seen in the profiler (click screenshot for a larger view).

As this is the initial value, a quick Sunday morning hack, it has not all features I can imagine. Things one could do include

• Provide information on caching decisions and behavior when mysqlnd_qc is used
• Provide replication-related decisions when the new mysqlnd replication and load balancing plugin is used
• Take David's mysqlnd_uh-based query logging ideas and provide more information on any executed query
• ....

Today we've released a few things for PHP and MySQL users: One is the first (and probably only) beta of the mysqlnd_ms plugin for MySQL Replication and Load Balancing support and the first GA version of a PHP plugin for the Query Analyzer of the MySQL Enterprise Monitor.

Ulf blogged a lot about mysqlnd_ms, so I don't have to repeat him here. what I want to talk about is the other one. So what is that about?

When running a PHP-based application with MySQL it is often quite interesting to see what actually happens on the database sever. Besides monitoring of the system load etc. it is often interesting to see what queries are actually executed and which of them are expensive. A part of MySQL Enterprise Monitor is the MySQL Query Analyzer which helps answering these questions.

Traditionally the MySQL Query Analyzer  was based on MySQL Proxy which is configured to sit between the application and the MySQL server and collects all relevant data.

Now in the new 2.3.7 release of the MySQL Enterprise Monitor we have enhanced this for PHP users: We now provide a plugin which can be loaded in PHP and which will provide data for the Query Analyzer directly from within PHP.

By that we don't only reduce the latency for the data collection but we can provide more information about the current environment.

In the query detail window you now don't only see general query statistics but also a stack trace from the application, so you can immediately identify the part of the application which should be improved. So above you can see a few screenshots I made from this server showing some insights of this blog where I was testing the plugin.

If you want to learn more checkout the documentation and product pages. Hope you like it!

Roughly three years ago I was writing about Direct MySQL Stream Access - a way to access the low-level stream PHP's mysqlnd library is using. Back then this had been a patch against PHP's mysqli extension. As such a feature is quite dangerous (you can easily mess with the connection state which confuses mysqlnd and/or the MySQL server) we didn't push it into the main PHP tree. Now three years later it's time to look at this again as we don't need to patch PHP anymore.

Since the mentioned patch was written mysqlnd got a plugin interface about which I was talking before. This plugin-interface, especially in the version of PHP 5.4, makes it trivial to implement this feature.

PHP_FUNCTION(mysqlnd_to_stream)
{
    zval *conn_zv;
    MYSQLND *conn;

    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "z", &conn_zv) == FAILURE) {
        return;
    }

    if (!(conn = zval_to_mysqlnd(conn_zv))) {
        php_error_docref(NULL TSRMLS_CC, E_WARNING,
                    "Passed variable is no mysqlnd based connection");
        RETURN_FALSE;
    }

    php_stream_to_zval(conn->net->stream, return_value);
}
 

If you take a function like the one shown above and add some general PHP infrastructure you are done. The key function here is the function MYSQLND* zval_to_mysqlnd(zval *connection) which takes a PHP variable as parameter and in case it is a MySQL connection (ext/mysql, mysqli or pdo_mysql) will return the corresponding MYSQLND pointer which gives access to the stream which then has to be packed into a PHP variable, again. The nice thing, compared to the old version is not only that it is a plugin which can be loaded into PHP as shared extension via php.ini but also that it works with all MySQL extensions, not only mysqli as the one before.

You can download the complete source, but be warned: This is experimental stuff and not supported in any way, but I hope good enough to get a feeling what's possible with mysqlnd.

Some time ago I was already writing about the power included with mysqlnd plugins and how they can they can be used transparently to help you with your requirements without changing your code. But well, as mysqlnd plugins in fact are regular PHP extensions they can export functions to the PHP userland and providing complete new functionality.

In my spare time I'm currently writing a shiny Web 2.0 application where I'm heavily using AJAX-like things, so what I do quite often in this application is, basically this: Check some pre-conditions (permissions etc.) then select some data from the database, do a fetch_all to get the complete result set as an array and run it through json_encode; or to have it in code:

<?php
$m = new MySQLi(/*...*/);
check_whether_the_user_is_checked_in_and_allowed_to_see_this();
$result = $m->query("SELECT a,b,c,d FROM t WHERE e=23");
echo json_encode($result->fetch_all());
?>

Of course that example is simplified as I'm using the Symfony 2 framework for this project. When writing a similar function for the 5th time I wondered whether I really need to create the temporary array and all these temporary elements in it.

So I wrote a mysqlnd plugin.

The mysqlnd_query_to_json plugin (hey what a name!) provides a single function, mysqlnd_query_to_json(), which takes two parameters, a connection identifier and an SQL query, and returns a JSON string containing the result set. The connection identifier can be a mysql resource, a mysqli object or even a PDO object. The resulting JSON string will be created directly from the network buffer without the need of temporary complex structures. Using the above example would create code like this:

<?php
$m = new MySQLi(/*...*/);
check_whether_the_user_is_checked_in_and_allowed_to_see_this();
echo mysqlnd_query_to_json($m, "SELECT a,b,c,d FROM t WHERE e=23");
?>

The plugin, which you can find here, requires PHP 5.4 and has a few limitations as it knows nothing about MySQL bitfields or escaping of unicode characters for creating fully valid JSON data and Andrey called it, for good reasons, a hack. Neither did I benchmark it, yet as I merely share it to show what's possible and maybe start some discussion on what is actually needed.

If you want to learn more on these topics I also suggest to check the MySQL Webinar page frequently as Ulf is going to hold a Webinar on myslqnd plugins in October!