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2. echo is faster than print. echo 比 print 快。
3. Use echo's multiple parameters instead of string concatenation. 使用echo的多重參數(shù)(譯注：指用逗號(hào)而不是句點(diǎn))代替字符串連接。
4. Set the maxvalue for your for-loops before and not in the loop. 在執(zhí)行for循環(huán)之前確定最大循環(huán)數(shù)，不要每循環(huán)一次都計(jì)算最大值。
5. Unset your variables to free memory, especially large arrays. 注銷那些不用的變量尤其是大數(shù)組，以便釋放內(nèi)存。
6. Avoid magic like __get, __set, __autoload 盡量避免使用__get,__set,__autoload.
7. require_once() is expensive require_once()代價(jià)昂貴。
8. Use full paths in includes and requires, less time spent on resolving the OS paths. 在包含文件時(shí)使用完整路徑，解析操作系統(tǒng)路徑所需的時(shí)間會(huì)更少。
9. If you need to find out the time when the script started executing, $_SERVER['REQUEST_TIME'] is preferred to time() 如果你想知道腳本開始執(zhí)行(譯注：即服務(wù)器端收到客戶端請(qǐng)求)的時(shí)刻，使用$_SERVER['REQUEST_TIME']要好于time()。
10. See if you can use strncasecmp, strpbrk and stripos instead of regex. 檢查是否能用strncasecmp,strpbrk,stripos函數(shù)代替正則表達(dá)式完成相同功能。
11. str_replace is faster than preg_replace, but strtr is faster than str_replace by a factor of 4. str_replace函數(shù)比preg_replace函數(shù)快，但strtr函數(shù)的效率是str_replace函數(shù)的四倍。
12. If the function, such as string replacement function, accepts both arrays and single characters as arguments, and if your argument list is not too long, consider writing a few redundant replacement statements, passing one character at a time, instead of one line of code that accepts arrays as search and replace arguments. 如果一個(gè)字符串替換函數(shù)，可接受數(shù)組或字符作為參數(shù)，并且參數(shù)長(zhǎng)度不太長(zhǎng)，那么可以考慮額外寫一段替換代碼，使得每次傳遞參數(shù)是一個(gè)字符，而不是只寫一行代碼接受數(shù)組作為查詢和替換的參數(shù)。
13. It's better to use select statements than multi if, else if, statements. 使用選擇分支語(yǔ)句(譯注：即switch case)好于使用多個(gè)if,else if語(yǔ)句。
14. Error suppression with @ is very slow. 用@屏蔽錯(cuò)誤消息的做法非常低效。
15. Turn on apache's mod_deflate 打開apache的mod_deflate模塊。
16. Close your database connections when you're done with them. 數(shù)據(jù)庫(kù)連接當(dāng)使用完畢時(shí)應(yīng)關(guān)掉。
17. $row['id'] is 7 times faster than $row[id]. $row['id']的效率是$row[id]的7倍。
18. Error messages are expensive. 錯(cuò)誤消息代價(jià)昂貴。
19. Do not use functions inside of for loop, such as for ($x=0; $x < count($array); $x) The count() function gets called each time. 盡量不要在for循環(huán)中使用函數(shù)，比如for ($x=0; $x < count($array); $x)每循環(huán)一次都會(huì)調(diào)用count()函數(shù)。
20. Incrementing a local variable in a method is the fastest. Nearly the same as calling a local variable in a function. 在方法中遞增局部變量，速度是最快的。幾乎與在函數(shù)中調(diào)用局部變量的速度相當(dāng)。
21. Incrementing a global variable is 2 times slow than a local var. 遞增一個(gè)全局變量要比遞增一個(gè)局部變量慢2倍。
22. Incrementing an object property (eg. $this->prop++) is 3 times slower than a local variable. 遞增一個(gè)對(duì)象屬性(如：$this->prop++)要比遞增一個(gè)局部變量慢3倍。
23. Incrementing an undefined local variable is 9-10 times slower than a pre-initialized one. 遞增一個(gè)未預(yù)定義的局部變量要比遞增一個(gè)預(yù)定義的局部變量慢9至10倍。
24. Just declaring a global variable without using it in a function also slows things down (by about the same amount as incrementing a local var)。 php probably does a check to see if the global exists. 僅定義一個(gè)局部變量而沒(méi)在函數(shù)中調(diào)用它，同樣會(huì)減慢速度(其程度相當(dāng)于遞增一個(gè)局部變量)。php大概會(huì)檢查看是否存在全局變量。
25. Method invocation appears to be independent of the number of methods defined in the class because I added 10 more methods to the test class (before and after the test method) with no change in performance. 方法調(diào)用看來(lái)與類中定義的方法的數(shù)量無(wú)關(guān)，因?yàn)槲?在測(cè)試方法之前和之后都)添加了10個(gè)方法，但性能上沒(méi)有變化。
26. Methods in derived classes run faster than ones defined in the base class. 派生類中的方法運(yùn)行起來(lái)要快于在基類中定義的同樣的方法。
27. A function call with one parameter and an empty function body takes about the same time as doing 7-8 $localvar++ operations. A similar method call is of course about 15 $localvar++ operations. 調(diào)用帶有一個(gè)參數(shù)的空函數(shù)，其花費(fèi)的時(shí)間相當(dāng)于執(zhí)行7至8次的局部變量遞增操作。類似的方法調(diào)用所花費(fèi)的時(shí)間接近于15次的局部變量遞增操作。
28. Surrounding your string by ' instead of " will make things interpret a little faster since php looks for variables inside "…" but not inside '…'. Of course you can only do this when you don't need to have variables in the string. 用單引號(hào)代替雙引號(hào)來(lái)包含字符串，這樣做會(huì)更快一些。因?yàn)?a href=/itjie/phpjishu/ target=_blank class=infotextkey>php會(huì)在雙引號(hào)包圍的字符串中搜尋變量，單引號(hào)則不會(huì)。當(dāng)然，只有當(dāng)你不需要在字符串中包含變量時(shí)才可以這么做。
29. When echoing strings it's faster to separate them by comma instead of dot. Note: This only works with echo, which is a function that can take several strings as arguments. 輸出多個(gè)字符串時(shí)，用逗號(hào)代替句點(diǎn)來(lái)分隔字符串，速度更快。注意：只有echo能這么做，它是一種可以把多個(gè)字符串當(dāng)作參數(shù)的"函數(shù)"(譯注：php手冊(cè)中說(shuō)echo是語(yǔ)言結(jié)構(gòu)，不是真正的函數(shù)，故把函數(shù)加上了雙引號(hào))。
30. A php script will be served at least 2-10 times slower than a static HTML page by Apache. Try to use more static HTML pages and fewer scripts. Apache解析一個(gè)php腳本的時(shí)間要比解析一個(gè)靜態(tài)HTML頁(yè)面慢2至10倍。盡量多用靜態(tài)HTML頁(yè)面，少用腳本。
31. Your php scripts are recompiled every time unless the scripts are cached. Install a php caching product to typically increase performance by 25-100% by removing compile times. 除非腳本可以緩存，否則每次調(diào)用時(shí)都會(huì)重新編譯一次。引入一套php緩存機(jī)制通常可以提升25%至100%的性能，以免除編譯開銷。
32. Cache as much as possible. Use memcached - memcached is a high-performance memory object caching system intended to speed up dynamic web applications by alleviating database load. OP code caches are useful so that your script does not have to be compiled on every request. 盡量做緩存，可使用memcached.memcached是一款高性能的內(nèi)存對(duì)象緩存系統(tǒng)，可用來(lái)加速動(dòng)態(tài)Web應(yīng)用程序，減輕數(shù)據(jù)庫(kù)負(fù)載。對(duì)運(yùn)算碼(OP code)的緩存很有用，使得腳本不必為每個(gè)請(qǐng)求做重新編譯。
33. When working with strings and you need to check that the string is either of a certain length you'd understandably would want to use the strlen() function. This function is pretty quick since it's operation does not perform any calculation but merely return the already known length of a string available in the zval structure (internal C struct used to store variables in php)。 However because strlen() is a function it is still somewhat slow because the function call requires several operations such as lowercase & hashtable lookup followed by the execution of said function. In some instance you can improve the speed of your code by using an isset() trick. 當(dāng)操作字符串并需要檢驗(yàn)其長(zhǎng)度是否滿足某種要求時(shí)，你想當(dāng)然地會(huì)使用strlen()函數(shù)。此函數(shù)執(zhí)行起來(lái)相當(dāng)快，因?yàn)樗蛔鋈魏斡?jì)算，只返回在zval結(jié)構(gòu)(C的內(nèi)置數(shù)據(jù)結(jié)構(gòu)，用于存儲(chǔ)php變量)中存儲(chǔ)的已知字符串長(zhǎng)度。但是，由于strlen()是函數(shù)，多多少少會(huì)有些慢，因?yàn)楹瘮?shù)調(diào)用會(huì)經(jīng)過(guò)諸多步驟，如字母小寫化(譯注：指函數(shù)名小寫化，php不區(qū)分函數(shù)名大小寫)、哈希查找，會(huì)跟隨被調(diào)用的函數(shù)一起執(zhí)行。在某些情況下，你可以使用isset()技巧加速執(zhí)行你的代碼。
Ex.(舉例如下)
if (strlen($foo) < 5) { echo "Foo is too short"; }
vs.(與下面的技巧做比較)
if (!isset($foo{5})) { echo "Foo is too short"; }
Calling isset() happens to be faster then strlen() because unlike strlen()， isset() is a language construct and not a function meaning that it's execution does not require function lookups and lowercase. This means you have virtually no overhead on top of the actual code that determines the string's length. 調(diào)用isset()恰巧比strlen()快，因?yàn)榕c后者不同的是，isset()作為一種語(yǔ)言結(jié)構(gòu)，意味著它的執(zhí)行不需要函數(shù)查找和字母小寫化。也就是說(shuō)，實(shí)際上在檢驗(yàn)字符串長(zhǎng)度的頂層代碼中你沒(méi)有花太多開銷。
34. When incrementing or decrementing the value of the variable $i++ happens to be a tad slower then ++$i. This is something php specific and does not apply to other languages, so don't go modifying your C or Java code thinking it'll suddenly become faster, it won't. ++$i happens to be faster in php because instead of 4 opcodes used for $i++ you only need 3. Post incrementation actually causes in the creation of a temporary var that is then incremented. While pre-incrementation increases the original value directly. This is one of the optimization that opcode optimized like Zend's php optimizer. It is still a good idea to keep in mind since not all opcode optimizers perform this optimization and there are plenty of ISPs and servers running without an opcode optimizer. 當(dāng)執(zhí)行變量$i的遞增或遞減時(shí)，$i++會(huì)比++$i慢一些。這種差異是php特有的，并不適用于其他語(yǔ)言，所以請(qǐng)不要修改你的C或Java代碼并指望它們能立即變快，沒(méi)用的。++$i更快是因?yàn)樗恍枰?條指令(opcodes)，$i++則需要4條指令。后置遞增實(shí)際上會(huì)產(chǎn)生一個(gè)臨時(shí)變量，這個(gè)臨時(shí)變量隨后被遞增。而前置遞增直接在原值上遞增。這是最優(yōu)化處理的一種，正如Zend的php優(yōu)化器所作的那樣。牢記這個(gè)優(yōu)化處理不失為一個(gè)好主意，因?yàn)椴⒉皇撬械闹噶顑?yōu)化器都會(huì)做同樣的優(yōu)化處理，并且存在大量沒(méi)有裝配指令優(yōu)化器的互聯(lián)網(wǎng)服務(wù)提供商(ISPs)和服務(wù)器。
35. Not everything has to be OOP, often it is too much overhead, each method and object call consumes a lot of memory. 并不是事必面向?qū)ο?OOP)，面向?qū)ο笸_銷很大，每個(gè)方法和對(duì)象調(diào)用都會(huì)消耗很多內(nèi)存。
36. Do not implement every data structure as a class, arrays are useful, too. 并非要用類實(shí)現(xiàn)所有的數(shù)據(jù)結(jié)構(gòu)，數(shù)組也很有用。
37. Don't split methods too much, think, which code you will really re-use. 不要把方法細(xì)分得過(guò)多，仔細(xì)想想你真正打算重用的是哪些代碼?
38. You can always split the code of a method later, when needed. 當(dāng)你需要時(shí)，你總能把代碼分解成方法。
39. Make use of the countless predefined functions. 盡量采用大量的php內(nèi)置函數(shù)。
40. If you have very time consuming functions in your code, consider writing them as C extensions. 如果在代碼中存在大量耗時(shí)的函數(shù)，你可以考慮用C擴(kuò)展的方式實(shí)現(xiàn)它們。
41. Profile your code. A profiler shows you, which parts of your code consumes how many time. The Xdebug debugger already contains a profiler. Profiling shows you the bottlenecks in overview. 評(píng)估檢驗(yàn)(profile)你的代碼。檢驗(yàn)器會(huì)告訴你，代碼的哪些部分消耗了多少時(shí)間。Xdebug調(diào)試器包含了檢驗(yàn)程序，評(píng)估檢驗(yàn)總體上可以顯示出代碼的瓶頸。
42. mod_gzip which is available as an Apache module compresses your data on the fly and can reduce the data to transfer up to 80%. mod_zip可作為Apache模塊，用來(lái)即時(shí)壓縮你的數(shù)據(jù)，并可讓數(shù)據(jù)傳輸量降低80%.
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