Why Is My AJAX POST Data Limited Even With High PHP Limits?

PHP/Apache/AJAX POST Data Limit

When attempting to send a large amount of data (2 million characters) via POST using AJAX (jQuery), the PHP side fails to retrieve the data and returns an "Undefined index" error. This issue is not related to the post_max_size setting in php.ini, which is sufficiently high (256M).

Investigating Limits

The problem lies in the multiple limits imposed by various components involved in the process:

1. Apache:

   • LimitRequestBody: Controls the maximum size of incoming POST requests. You should check your Apache error logs to determine the actual limit, which is generally around 2GB by default.

2. PHP:

   • post_max_size: Limits the size of POST data. Ensure this setting is set high enough in your php.ini (e.g., 256M).
   • upload_max_filesize: Although unrelated to POST data, it's worth mentioning for completeness.
   • max_input_time: Controls the maximum time allowed for POST data processing. Set it to a large value to avoid timeouts (e.g., -1).
   • max_input_nesting_level: Limits the depth of nested arrays in POST data. If your data contains deeply nested arrays, you may need to increase this value.
   • max_execution_time: Unlikely to be the cause of the issue.
   • memory_limit: Ensures that the PHP subprocess has ample memory to handle the data. Adjust this setting accordingly (e.g., 256M).
   • max_input_vars: Limits the number of variables in POST requests. If your data contains a large number of elements, you may need to increase this value.

Solution

If Apache's LimitRequestBody is reached, you cannot directly POST the data as it exceeds the compiled-in limit. You must break the data into smaller chunks and send it in multiple POST requests.

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