Parsing large file using php linux server - php

Question

I am a php programmer and currently I am working with files. I have to parse and insert the data to mysql database. Since its large amount of data php unable to load or parse the file. I am getting memory leak error even though I have increased memory_limit upto 1500MB.
FATAL: emalloc(): Unable to allocate 456185835 bytes
my text file contains text and xml data. I have to parse the xml data from the text file.
eg: <ajax>some text goes here</ajax> non relativ text <ajax>other content</ajax>
In the above example I have to parse the content inside tag. If any one can give some advice to separate each tag into individual file(eg: 1.txt, 2.txt), it will be great(perl or c or shell scripting..etc ).

Answer 1

Cough... a 1500 MB memory limit is a sure sign you have gone off the rails.
Where are you getting your file? I assume (given the size) that this is a local file. If you are trying to load the file into a string using file_get_contents() it is worth noting that the docs are wrong and that said function does not in fact using memory-mapped I/O (cf. bug 52802). So this is not going to work for you.
What you might try is instead falling back to more C-like (but still PHP) constructs, in particular fopen(), fseek(), and fread(). If the file is of a known structure with newlines, you might also consider fgets().
These should allow you to read in bytes in chunks into a reasonable size buffer from which you can do your processing. Since it looks like you are processing tagged strings, you will have to play the usual games of keeping multiple buffers around in which you can accumulate data until processable. This is fairly standard stuff covered in most introductions to, e.g., stream processing in C.
Note that in PHP (or any other language for that matter), you are also going to have to potentially consider issues of string encoding because, in general, it is no longer the case that 1 byte == 1 character (cf. Unicode).
As you insinuate, PHP may well not be the best language for this task (though it certainly can do it). But your problem isn't really a language-specific one; you are running into a fundamental limitation of handling large files without memory-mapping.

Answer 2

you can actually parse XML with PHP a small block at a time so you dont actually require much ram at all:
set_time_limit(0);
define('__BUFFER_SIZE__', 131072);
define('__XML_FILE__', 'pf_1360591.xml');
function elementStart($p, $n, $a) {
//handle opening of elements
}
function elementEnd($p, $n) {
//handle closing of elements
}
function elementData($p, $d) {
//handle cdata in elements
}
$xml = xml_parser_create();
xml_parser_set_option($xml, XML_OPTION_TARGET_ENCODING, 'UTF-8');
xml_parser_set_option($xml, XML_OPTION_CASE_FOLDING, 0);
xml_parser_set_option($xml, XML_OPTION_SKIP_WHITE, 1);
xml_set_element_handler($xml, 'elementStart', 'elementEnd');
xml_set_character_data_handler($xml, 'elementData');
$f = fopen(__XML_FILE__, 'r');
if($f) {
while(!feof($f)) {
$content = fread($f, __BUFFER_SIZE__);
xml_parse($xml, $content, feof($f));
unset($content);
}
fclose($f);
}