Why Am I Receiving \"Undefined Index\" Errors When Sending Large POST Data to PHP?

Content Too Big for PHP POST

You are experiencing difficulties sending POST data that exceeds 2 million characters via AJAX to PHP. Specifically, you encounter an "Undefined index" error when attempting to retrieve the data from $_POST['data_string'].

Apache Limits

Firstly, consider the limits imposed by Apache. Check the LimitRequestBody parameter, which typically defaults around 2Gb. If your data size surpasses this limit, you may observe errors in the Apache error logs.

PHP Configuration

Next, examine the PHP configuration settings:

• post_max_size: This parameter directly governs the maximum POST size. Ensure it is set to a value greater than 256M.
• upload_max_filesize: Though unrelated, this setting may also impact file uploads, which could potentially interfere with your request.
• max_input_time: Adjust this setting to prevent the POST operation from exceeding a certain time limit.
• max_input_nesting_level: If your data contains deeply nested arrays, this limit may need increasing.
• max_execution_time: This setting is unlikely to affect the issue.
• memory_limit: Verify that your data size does not exceed the memory limit allocated to the PHP subprocess.
• max_input_vars: Ensure this parameter is set high enough to accommodate the number of elements in the POST data array.

Other Considerations

If you confirm that the Apache and PHP limits are sufficient, consider the following:

• Check the size of the data you are attempting to send.
• Ensure that the browser is not limiting data transmission.
• Examine the server logs for any additional error messages.

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