Performance Guidelines

Table of Contents

• POSIX Extended Regular Expressions
• Perl-compatible (PCRE) Regular Expressions
• PCRE Subpattern Capture Optimization
• Avoid Unnecessary String Replacements
• Smart Substring Matching
• for() Loops
• Heredoc Strings
• One-time Use Variables
• Redundant Queries

Guidelines

• POSIX Extended Regular Expressions

  Do not use POSIX Extended regular expression functions. When you need a regular expression function, always use the Perl-compatible (PCRE) preg_ functions.

  NEVER USE: ereg() eregi() ereg_replace() eregi_replace() split() spliti() sql_regcase()

• Perl-compatible (PCRE) Regular Expressions

  Do not use regular expression functions unless you need to.

  INCORRECT: $str = preg_replace('/foo/', 'bar', $str); $arr = preg_split('|', $str); $arr = preg_split('|', $str, -1, PREG_SPLIT_NO_EMPTY); // $str is '1|2|3|4|' CORRECT: $str = str_replace('foo', 'bar', $str); $arr = explode('|', $str); $arr = explode('|', trim($str, '|')); // $str is '1|2|3|4|'

• PCRE Subpattern Capture Optimization

  Use ?: at the start of a subpattern if it does not need to be captured for faster execution and memory conservation.

  INCORRECT: $str = preg_replace('/xyz([0-9]+)/', 'zyx', $str); // not using the captured subpattern, so ?: should be used CORRECT: $str = preg_replace('/xyz(?:[0-9]+)/', 'zyx', $str); // correct use when not using the captured subpattern $str = preg_replace('/xyz([0-9]+)/', 'zyx\\1', $str); // correct use of a captured subpattern

• Avoid Unnecessary String Replacements

  Do not perform string replacements unless you need to, and know that the search string exists in the subject string. Use strpos() to see if the replacement is necessary beforehand.

  INCORRECT: foreach ($items as $name => $value) { $str = str_replace($name, $value, $str); } CORRECT: foreach ($items as $name => $value) { if (strpos($str, $name) !== FALSE) { $str = str_replace($name, $value, $str); } }

  Remarkably, even if a match occurs on each loop, the additional processing overhead for the strpos() is negligible (on a 100kb string it adds roughly 0.01 seconds for every 10,000 loops). If there are loops that do not match, this method can approach 100% greater efficiency.

• Smart Substring Matching

  When checking to see if a string has matching characters at the front of the string only, use strncmp() and strncasecmp() instead of substr(). Especially on non-case sensitive checks, these functions are much faster. Never use regular expression functions for this unless you actually need a regular expression match.

  INCORRECT: if (substr($str, 0, 3) == 'foo') if (substr(strtolower($str), 0, 3) == 'foo') if (preg_match('/^foo/', $str)) // no need for regex match for this type of comparison if (ereg('^foo', $str)) // AAAAAH! Never ever use ereg(), remember? CORRECT: if (strncmp($str, 'foo', 3) == 0) if (strncasecmp($str, 'foo', 3) == 0)

  strncmp() and strncasecmp() return < 0 if str1 is less than str2, > 0 if str1 is greater than str2, and 0 if they are equal.

• for() Loops

  Do not perform calculations in the second expression of for() loops, as they will be executed on each iteration of the loop. Perform them either in the first expression, or before entering the loop.

  INCORRECT: for ($i = 0; $i < count($arr); $i++) CORRECT: for ($i = 0, $foo = $count($arr); $i < $foo; $i++) ALTERNATIVE: $foo = count($arr); for ($i = 0; $i < $foo; $i++)

• Heredoc Strings

  Avoid heredoc strings unless absolutely necessary. They are more intensive for PHP to parse than single or double-quoted strings, resulting in slower code execution and increased memory usage.

• One-time Use Variables

  Avoid assigning new variables for one-time use. In the example below, $foo is never used again in the method.

  INCORRECT: $foo = 'a'; $str = $str.$foo; CORRECT: $str = $str.'a';

• Redundant Queries

  Avoid running queries in loops or running identical queries multiple times across page loads. Find a way to run such queries only once, outside of loops, by perhaps accessing all of the information your add-on will require for each iteration, storing it in a master array.

  Make intelligent use of $SESS->cache so these and other "meta" queries are executed only once no matter how many times a method is called on a page load.

  NOTE: To keep the code example simple, the values in the $ids array below are assumed to have already been validated in the code prior to what is being shown. Do not neglect to validate and escape variables before using them in queries!

  INCORRECT: foreach ($ids as $id) { $query = $DB->query("SELECT name FROM exp_pre_email_addresses WHERE id = {$id}"); if ($query->num_rows > 0) { $name = $query->row['name']; // rest of the code } } CORRECT: if ( ! isset($SESS->cache['super_class']['names'])) { $query = $DB->query('SELECT id, name FROM exp_pre_email_addresses WHERE id IN ('.implode(',', $ids).')'); if ($query->num_rows > 0) { foreach ($query->result as $row) { $SESS->cache['super_class']['names'][$row['id']] = $row['name']; } } } $names = $SESS->cache['super_class']['names']; // later in the code looped queries are no longer used foreach ($ids as $id) { $name = $names[$id]; // rest of the code }