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![public function foo($file1, $file2){
$obj = new Obj();
$data = array();
$data[] = $obj->importAFile($file1);
$data[] = $obj->importAFile($file2);
return $data;
}](https://image.slidesharecdn.com/allowedmemory-131027152150-phpapp02/85/PHPConPl-2013-Allowed-memory-size-of-X-bytes-exhausted-19-320.jpg)
![public function foo($file1, $file2){
$obj = new Obj();
$data = array();
$data[] = $obj->importAFile($file1);
$data[] = $obj->importAFile($file2);
return $data;
}](https://image.slidesharecdn.com/allowedmemory-131027152150-phpapp02/85/PHPConPl-2013-Allowed-memory-size-of-X-bytes-exhausted-23-320.jpg)
Uploaded byPiotr Pasich
PHPConPl 2013 - Allowed memory size of X bytes exhausted
The document discusses PHP memory usage and management. It explains that variables in PHP use more memory than in C due to overhead from structured like zvals. Different areas that consume memory are the heap, extensions, and parsed code. Techniques for monitoring and reducing memory usage include Xdebug profiling, OPcache, and avoiding unnecessary variable references. Managing memory leaks and optimizing data structures can help applications use memory efficiently.
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PHPConPl 2013 - Allowed memory size of X bytes exhausted
- 1. Allowed memory size ofX bytes exhausted Piotr Pasich piotr.pasich @xsolve.pl @piotrpasich
- 2. „A good understanding ofhow variables are stored and manipulated is essential to becoming a Hacker.” php.net
- 3. „A good understanding ofhow variables are stored and manipulated is essential to becoming a Hacker.” php.net
- 4. Have you everthought why don't you do this?
- 5. public function foo() { $a= new stdClass; $b = array(); //(...) unset($a); unset($b); return; }
- 6. It might savememory
- 7.
- 8.
- 9.
- 10.
- 12.
- 13. It's mostly usedto store variables in functions
- 14. So, variables liveonly in functions
- 15. Not PHP functions, butC functions
- 16. One PHP function!= One C function
- 17. They are allocated andfreed automatically
- 18. At function returnthe stack is popped
- 19. public function foo($file1,$file2){ $obj = new Obj(); $data = array(); $data[] = $obj->importAFile($file1); $data[] = $obj->importAFile($file2); return $data; }
- 20. Does the memoryallocated for $obj get freed after the return?
- 21.
- 22. And when itisn't?
- 23. public function foo($file1,$file2){ $obj = new Obj(); $data = array(); $data[] = $obj->importAFile($file1); $data[] = $obj->importAFile($file2); return $data; }
- 24.
- 25. It frees allvariables to which there are no references left
- 26.
- 27.
- 29.
- 30. No limit onmemory size*
- 31. You have tomanage it
- 32. Variables can beaccessed globally
- 33.
- 34.
- 35.
- 36.
- 37.
- 38.
- 39.
- 40.
- 41.
- 42.
- 43. more code ==more memory
- 44. more code ==more time
- 45.
- 46.
- 47. sudo pecl installzendopcache-7.0.2
- 48.
- 49. Stores precompiled script bytecode inshared memory
- 51.
- 52.
- 53.
- 54.
- 55. $startMemory = memory_get_usage(); $array= range(1, 100000); echo memory_get_usage() - $startMemory, ' bytes';
- 56. C 100 000 *8 bytes = 800 000 bytes
- 57. PHP 14 649 016bytes
- 58.
- 59. All variables are represented byone structure
- 60.
- 61. typedef struct _zval_struct{ zvalue_value value; /* variable value */ zend_uint refcount__gc; /* reference counter */ zend_uchar type; /* value type */ zend_uchar is_ref__gc; /* reference flag */ } zval;
- 62. typedef union _zvalue_value{ long lval; /* long value */ double dval; /* double value */ struct { char *val; int len; /* this will always be set for strings */ } str; /* string (always has length) */ HashTable *ht; /* an array */ zend_object_value obj; /* stores an object store handle, and handlers */ } zvalue_value;
- 63. Each variable needs muchmore memory than in C
- 64. | 64 bit| 32 bit --------------------------------------------------zval | 24 bytes | 16 bytes + cyclic GC info | 8 bytes | 4 bytes + allocation header | 16 bytes | 8 bytes =================================================== zval (value) total | 48 bytes | 28 bytes =================================================== bucket | 72 bytes | 36 bytes + allocation header | 16 bytes | 8 bytes + pointer | 8 bytes | 4 bytes =================================================== bucket (array element) total | 96 bytes | 48 bytes =================================================== total total | 144 bytes | 76 bytes
- 65. 144 bytes *100 000 = 1 440 0000
- 66. What happened to therest 249 016 bytes?
- 67.
- 68. 2^17 = 131072 131 072 – 100 000 = 31 072 pointers
- 69. 31 072 pointers* 8 bytes = 248 576 missing bytes
- 70.
- 71. We can useSplFixedArray
- 72. That’s 56 bytesper element
- 73. SplFixedArray is writting 33% faster reading 10% faster
- 74. Uff, now youknow a lot
- 75. „Am I ahacker now?”
- 76. Not yet, waita second
- 77. Be like aninja!
- 78.
- 79. PHP Fatal Error:Allowed memory size of 8388608 bytes exhausted
- 80.
- 81.
- 82.
- 83. Fatal error: Allowedmemory size of 33554432 bytes exhausted (tried to allocate 2798048 bytes) in /***/app/http.php on line 6331
- 84.
- 85. Let’s move toanother
- 86.
- 87.
- 88. You can debugit step by step
- 90.
- 91.
- 92.
- 93.
- 94.
- 95.
- 96. Default 0.0004 114272 ->str_split() ../trace.php:8 0.0153 117424 -> ret_ord() ../trace.php:10 1 0.0004 0.0007 114272 117424 -> str_split(string(6)) ../trace.php:8 -> ret_ord(string(1)) ../trace.php:10 3 0.0004 0.0007 114272 117424 -> str_split('Xdebug') ../trace.php:8 -> ret_ord('X') ../trace.php:10 4 0.0004 0.0007 114272 117424 -> str_split('Xdebug') ../trace.php:8 -> ret_ord($c = 'X') ../trace.php:10
- 97.
- 98.
- 99. You can useWebgrind
- 100. You can useWebgrind
- 101.
- 104.
- 105.
- 106.