Don't think that using references will lower your RAM usage
Objects are always copied by reference in PHP 5, which means that copying even the most complex object is instantaneous and essentially free in terms of memory usage. Furthermore, PHP makes extensive use of "copy-on-write", which means taking ten copies of the same array is also free, because they all point to the same object. It's called "copy-on-write" because the minute one of the arrays change from the others, a full copy is made so the change is kept separate.
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Pre-increment where possible
Performance Optimising your code Write your code sensibly Use your tools wisely Avoid functions for maximum performance Use the Zend Optimizer Use a PHP code cache Read the manual carefully Get your loops right first Pre-increment where possible Don't think that using references will lower your RAM usage Be wary of garbage collection, part 1 Be wary of garbage collection, part 2 Listen to all errors, big and small Keep up to date Cache array data Compress your output Don't use CGI Don't use dl() Debug your code Cache your pages Use persistent connections Take advantage of new features Compile right Ignore the myths Avoid mod_access if you can Don't fret about Apache 2.0 Optimising your SQL Prioritise your data Optimise your tables Select as little data as possible Use shorter queries where possible Use the EXPLAIN statement Change your hardware Choose your data types carefully Size vs. Speed Declare fields NOT NULL Load data intelligently Consider splitting off variable-length fields Be wary of locks Consider switching OS Spot slow queries Perform joins carefully Index your data Make sure your indexes are being used Normalisation Upgrade MySQL Increase your buffers Keep tabs on your server Lock your tables when appropriate Don't rely on automatic type conversion Benchmark, benchmark, benchmark! Know MySQL's strengths Server PHP Accelerators Caching PHP PHP as a CGI or a module? Size of scripts Summary Exercises Further reading Next chapter
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