How can I store large chunks into json file without memory crash?

You could do something like this as you mentioned you know how to use array_chunk();Let's look into simplifying the process with a built-in PHP function called array_chunk();

We'll be using HTML tables for design which isn't recommended. The task is better accomplished with CSS, you can follow same way without HTML and CSS.

Our table :

id  datePosted  firstName   lastName    pictureName          anotherColumn1   2013-07-01  John        Smith       SmithJohn.jpg        anotherValue2   2013-05-06  Elroy       Johnson     JohnsonElroy.jpg     anotherValue3   2013-06-18  Jake        Bible       BibleJake.jpg        anotherValue4   2013-07-17  Steve       Stevenson   StevensonSteve.jpg   anotherValue5   2013-04-08  Bill        Smith       SmithBill2.jpg       anotherValue

Building HTML Tables

PDO query is used to grab the database information with prepared statements, Note that the loop only generates the code to display the columns.The tests to detect where the rows begin and end are unnecessary.

//INITIALIZE VARIABLES$colsToDisplay = 3;$htmlOutput    = array();//GET PICTURE LIST$sql = "SELECT datePosted, firstName, lastName, pictureName FROM pictureList ORDER BY datePosted DESC";$stmt = $pdo->prepare($sql);$stmt->execute();while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {     $htmlOutput[] = "<td><img src='images/{$row['pictureName']}' alt='' /><br />{$row['firstName']} {$row['lastName']}</td>";}

Once the loop is done, the array containing the column information can be broken into groups of three... or whatever value was assigned to $colsToDisplay, What we did here ? we tooks 3 columns from table, So divide table in two parts.

while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {     //...}//BREAK THE COLUMNS INTO GROUPS$htmlOutput = array_chunk($htmlOutput, $colsToDisplay);

All that's left is to display the table information. Note that array_chunk() creates a multi-dimensional array. The foreach loop is used to process the groups of columns. Each group is assigned to $currRow which contains an array of columns for the current row. The implode() function is used to quickly display the columns as a string.

Lets continue :

//BREAK THE COLUMNS INTO GROUPS$htmlOutput = array_chunk($htmlOutput, $colsToDisplay);//DISPLAY TABLEprint '<table>';foreach($htmlOutput as $currRow) {     print '<tr>' . implode('', $currRow) . '</tr>';}print '</table>';

Checking For Missing Column Tags

One thing you may have noticed is the code to add missing columns was left out.In other words, this example results in an HTML table where the last row only has two columns.

Apparently, the missing columns aren't needed according to the W3C Markup Validation Service… so they weren't included. However, they can be added by running the following code right before array_chunk() is called.

$colsDifference = count($htmlOutput) % $colsToDisplay;if($colsDifference) {     while($colsDifference < $colsToDisplay) {                   $htmlOutput[] = '<td></td>';                   $colsDifference++;    } } 

Final Code :

    //INITIALIZE VARIABLES    $colsToDisplay = 3;    $htmlOutput    = array();    //GET PICTURE LIST    $sql = "SELECT datePosted, firstName, lastName, pictureName FROM pictureList ORDER BY datePosted DESC";    $stmt = $pdo->prepare($sql);    $stmt->execute();    while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {         $htmlOutput[] = "<td><img src='images/{$row['pictureName']}' alt='' /><br />{$row['firstName']} {$row['lastName']}</td>";    }    //OPTIONAL CODE    //IF NEEDED, ADD MISSING COLUMNS    $colsDifference = count($htmlOutput) % $colsToDisplay;    if($colsDifference) {         while($colsDifference < $colsToDisplay) {                       $htmlOutput[] = '<td></td>';                       $colsDifference++;              }    }         //END: OPTIONAL CODE          //BREAK THE COLUMNS INTO GROUPS    $htmlOutput = array_chunk($htmlOutput, $colsToDisplay);           //DISPLAY TABLE print '<table>';     foreach($htmlOutput as $currRow) {              print '<tr>' . implode('', $currRow) . '</tr>';     }     print '</table>'; 

Idea Behind This Tutorial :

1. You dont need to create a file and write arrays into that file to display in datatable.
2. If you still wants that you can (divide table in two parts) to create two arrays and than write into file, and than use array_push(); or array_merge(); to get both arrays into one.

I might have bad explanition please forgive for mistakes, Hope this help you in your coding life :)

Sticking to your solution, you can append the other chunks to your exisiting file. This works by setting the flag FILE_APPEND, e.g.:

$table_json = $serializer->serialize($table[1], 'json', $context);$myfile = fopen($_SERVER['DOCUMENT_ROOT']."/files/myfile.json", "w") or die("Unable to open file!");file_put_contents($_SERVER['DOCUMENT_ROOT']."/files/myfile.json", $table_json, FILE_APPEND | LOCK_EX);

(LOCK_EX flag to prevent anyone else writing to the file at the same time)