Just another programmer's blog

It is a quite common problem when cache is expired and multiple PHP processes are trying to update it. There is even a special term for this - "cache slam". The "cache slam" problem is described very good on php.net " If a highly shared cache entry stored, for example, in Memcache expires, many clients gets a cache miss. Many client requests can no longer be served from the cache but try to run the underlying query on the database server. Until the cache entry is refreshed, more and more clients contact the database server. In the worst case, a total lost of service is the result. " You can't do $memcached->set('lock_xyz') and then in some other place if ($memcached->get('lock_xyz')) like described in a lot of suggestions all over the internet. Imaging that 10 processes in parallel are trying to check whether lock exists and if not - set it. All of them will end up with setting the lock and do the cache refresh process. I

Sometimes you need to profile your queries with EXPLAIN to see what makes it slow. To do this you need a real SQL query, not DQL. Of course you can take it from Symfony Debug page, but it won't contain binded data, only "?" marks and the parameters that Doctrine binds. It is quite boring to insert them manually, you loose your time on this, can make a mistake etc. I wrote a simple logger, that can log query with inserted parameters. Installation: composer require --dev cmyker / doctrine - sql - logger : dev - master Usage: $connection = $this -> getEntityManager ()-> getConnection (); $logger = new \Cmyker\DoctrineSqlLogger\Logger ( $connection ); $connection -> getConfiguration ()-> setSQLLogger ( $logger ); //some query here echo $logger -> lastQuery ; //or see the output

Generators support was introduced in PHP 5.5. The yield keyword is a really cool thing that allows to write an elegant and memory efficient code. It was existing in another dynamic languages like python for quite a long time and now it is in PHP as well! To demonstrate generators concept, i wrote a sample function that  yields  all permutations of the given array and avoids of data copying on recursive calls: function permute( $array ) { $length = sizeof( $array ); $inner = function ( $ix = []) use ( $array , $length , & $inner ) { $yield = sizeof( $ix ) == $length - 1 ; for ( $i = 0 ; $i < $length ; $i ++) { if (in_array( $i , $ix )) { continue ; } elseif ( $yield ) { $toYield = []; foreach (array_merge( $ix , [ $i ]) as $index ) { $toYield [] = $array [ $index ]; } yield $toYield ; } el