PHP Tutorials - Herong's Tutorial Examples - v5.17, by Herong Yang
memory_get_usage() - Memory Usage Info
This section provides a tutorial example on how to the memory_get_usage() function to get memory usage information. ini_set('memory_limit', '256M') can be used increase memory limit. unset($o) can be used from objects from memory.
If you are running PHP scripts that use large objects, repeating loops, and/or recursive calls, you may experience system memory issues. There are several functions that allows you to query and manage system memories:
Here is simple PHP script to demonstrate above functions:
<?php # memory-test.php #- Copyright 2003 (c) HerongYang.com. All Rights Reserved. echo "Memory usage report:"."\n"; $total = memory_get_usage(True); $used = memory_get_usage(False); echo " Total memory: ".$total."\n"; echo " Used memory: ".$used."\n"; echo "Memory test on string object (10Ki) allocatin:"."\n"; $before = memory_get_usage(); $o = str_repeat("Hello PHP!", 1024); # 10,240 byte-string $after = memory_get_usage(); unset($o); $final = memory_get_usage(); echo " Memory used before allocation: ".$before."\n"; echo " Memory used used by the string: ".($after-$before)."\n"; echo " Memory freed up by the string: ".($after-$final)."\n"; echo "Increase memory upper limit:"."\n"; $before = ini_get('memory_limit'); ini_set('memory_limit', '256M'); $after = ini_get('memory_limit'); echo " Memory limit before: ".$before."\n"; echo " Memory limit after: ".$after."\n"; ?>
Below is the output of the above script on my Linux computer:
herong$ php memory-test.php Memory usage report: Total memory: 262144 Used memory: 227512 Memory test on string object (10Ki) allocatin: Memory used before allocation: 227600 Memory used used by the string: 10536 Memory freed up by the string: 10264 Increase memory upper limit: Memory limit before: 128M Memory limit after: 256M
Note that:
If you get a memory overflow error message, you should view the reported memory size and object size that caused the overflow. For example, the following error message says that PHP engine failed to allocate an object of 12,288 bytes (a small object) at line 1,291. So the code before this line has consumed almost the entire memory of 134,217,728 bytes. You need to review the code to ensure there is no memory leaks.
Allowed memory size of 134,217,728 bytes exhausted (tried to allocate 12288 bytes) in some-script.php on line 1291.
However, the following error message says that PHP engine failed to allocate an object of 331,776 bytes (a large object) at line 1,291. So maybe this time, this large object is questionable. Why this object is so big?
Allowed memory size of 268435456 bytes exhausted (tried to allocate 331776 bytes) in other-script.php on line 159.
Table of Contents
Introduction and Installation of PHP
PHP Data Types and Data Literals
Variables, References, and Constants
Expressions, Operations and Type Conversions
Conditional Statements - "if" and "switch"
Loop Statements - "while", "for", and "do ... while"
Function Declaration, Arguments, and Return Values
►Interface with Operating System
$argv[] - Command Line Arguments
Options to Execute External Programs
exec() - Execute External Programs
system() - Execute External Programs
passthru() - Execute External Programs
popen() - Execute External Programs
proc_open() - Execute External Programs
►memory_get_usage() - Memory Usage Info
set_time_limit() - max_execution_time
Introduction of Class and Object
Integrating PHP with Apache Web Server
Retrieving Information from HTTP Requests
Creating and Managing Sessions in PHP Scripts
Sending and Receiving Cookies in PHP Scripts
Controlling HTTP Response Header Lines in PHP Scripts
MySQL Server Connection and Access Functions
Functions to Manage Directories, Files and Images
SOAP Extension Function and Calling Web Services
SOAP Server Functions and Examples
Localization Overview of Web Applications
Using Non-ASCII Characters in HTML Documents
Using Non-ASCII Characters as PHP Script String Literals
Receiving Non-ASCII Characters from Input Forms
"mbstring" Extension and Non-ASCII Encoding Management
Managing Non-ASCII Character Strings with MySQL Servers
Parsing and Managing HTML Documents
Configuring and Sending Out Emails
Managing PHP Engine and Modules on macOS