General tips for writing lean fast php code

[joflow]

I have a feeling that the php code for a site I'm working on is very slow. It seems like its taking a few seconds for my host to process the script and thats just with one person browsing. Are there any general tips out there for writing lean fast code.

[viv5]

Check out this post:

PHP and MySQL coding tips

[ServerStorm]

Some general tips:

1. narrow database queries scope: instead of doing Select * from someTable do Select * from someTable Where xxx or Select * from someTable Select * from someTable Limit 5, 10. If you have even just one query of an entire table it can kill the speed of you application; or many non-narrowed queries can also lead to slow results
2. If using classes, include them when they are needed rather than loading classes that are not used for the current execution.
3. Use single quotes whenever possible (rather than double quotes)
4. Employ Chunked Buffering to Cache for a long time the parts of your pages that rarely change, and regularly update areas of frequent use by having short caching periods. Rather than writing your own caching engine you might consider using PEARS Cache_Lite class.
5. Write code so that you have only the minimum amount of code to service the job. Look for places where tasks are being repeated and roll functions to reduce the scope of code that needs traversing. For example write functions that are polymorphic or use Object Orient Programming (OOP) and write classes that utilize Inheritance, Polymorphism, Aggregation, and Composition. By combining OOP with Caching you can write less code and have good performance. For a great case on why to use OOP read this http://www.sitepoint.com/forums/showthread.php?t=59898 thread. little plug for OOP.
6. Don't do things like this:

for ($i = 1; i <= COUNT($Units); ++$i){
                echo "$i";
  } 

Instead do this:

  $count = COUNT($Units);
   for ($i = 1; i <= $count; ++$i){
                 echo "$i";
   } 

calling functions in loops again and again can be costly on speed and memory. When possible try to re-write loops such that the any static values required for the loop's evaluation are determined before the loop is run.

Hope some of this helps,
ServerStorm

[Vennie]

Regarding SQL

Select * from someTable

Rather then doing select *, only specify the columns you really need:
SELECT column1, column2, column3 FROM sometable

Never nest mysql queries. So do NOT do this:

$sQuery = 'SELECT id FROM table1';
$rsResult = mysql_query($sQuery);
while($aRow = mysql_fetch_assoc($rsResult)){
  $sQuery = 'SELECT column1, column2, column3 FROM table2 WHERE id = '.$aRow['id'];
  // etcetera
} 

Also: instead of performing multiple queries, try using joins (on well-indexed tables)

[stereofrog]

I have a feeling that the php code for a site I'm working on is very slow. It seems like its taking a few seconds for my host to process the script and thats just with one person browsing. Are there any general tips out there for writing lean fast code.

Well generally there is no "general" tips. You'll need to profile your application first to find out what exactly slows it down.