What is the size limit of a php variable when storing a string?

Question

This is so: I have a 2Gb dump file named myDB.sql . This is a dump file that deletes an existing database and creates a new one, with views and triggers. Therefore, I have a line myDB_OLD spread for many lines of code. I would like to change these string occurrences to myDB_NEW . I could do this easily using notePad ++. But notepad does not open a 2Gb file. What I did is PHP code that reads line by line and finds and replaces the line I want.

This is the code:

 $myfile2 = fopen("myDB.sql", "r") or die("Unable to open file!");//Reads the file while (!feof($myfile2)) {//Pass trough each line $str=fgets($myfile2);//Store the line inside a variable if (preg_match("/myDB_OLD/",$str)) {//If the string I want to change exists - replace it and conacatenate $newStr .= str_replace("myDB_OLD","myDB_NEW",$str); } else {//If not concatenate it $newStr .=$str; } }//End of while fclose($myfile2); //Save the newStr in a new file named $myfile = fopen("newDB.sql", "w") or die("Unable to open file!"); fwrite($myfile, $newStr); echo "finished"; 

This code extracts each line of the file, changes the line, concatenates in the variable, and creates a new file. It should work, but it is not. I do not know why. I use xdebug to find out what the problem is, but no luck.

Therefore, I am changing the approach. Instead of saving each line in a variable, I save it directly to a file and this works well.

This is the new code:

 $myfile = fopen("newDB.sql", "w") or die("Unable to open file!");//Creates a new file "newDB.sql" $myfile2 = fopen("myDB.sql", "r") or die("Unable to open file!");//Reads the file while (!feof($myfile2)) {//Pass trough each line $str=fgets($myfile2);//Store the line inside a variable if (preg_match("/myDB/",$str)) {//If the string I want to change exists - replace it . (Do not concatenate) $strRep=str_replace("myDB","myDB_NEW",$str); } else { $strRep =$str; } fwrite($myfile, $strRep);// Add the new line to the file "newDB.sql" }//End of while fclose($myfile); fclose($myfile2); echo "finished"; 

Well, I solved my problem, but it causes a thought. What is the problem of the first code? I think the problem is the amount of information that needs to be stored in the PHP variable, 2Gb. So, is there a size limit on the size of a PHP variable to hold a value, in this case a string? If so, how can I check or change it? Any php.ini variable?

Answer 1

So, is there a size restriction on the Php variable for storing the value, in this case a string?

Yes. The string can reach 2 GB (maximum 2147483647 bytes) . You cannot override this limit by increasing the memory_limit directive in php.ini.

There is no such restriction from php7 on a 64-bit system:

Support for strings with a length> = 2 ^ 31 bytes in 64-bit assemblies.

Answer 2

The maximum number of bytes a script is allowed to allocate is set in php.ini. Find memory_limit . This is 16Mb after PHP 5.2.0 by default!

You can change this by following these steps:

 ini_set('memory_limit','24M'); 

The maximum row size is 2 GB in PHP, probably due to access restrictions if memory_limit allowed.