如果行数大于6400，PHP / MySQL不会返回任何结果

I am using simple PHP query to fetch rows from the database, there are above 7000 rows in the table and whenever I fetch all rows, the PHP doesn't work and script dies, but when I limit the results to 6400 everything works fine. Is there any limitation in MySQL or PHP that I should be aware of? If any, where I need to configure these settings. Any help is highly appreciated. Please note that my PHP settings allow the script execution time of 1800 seconds and memory usage is set to 512MB.I am using simple PHP query to fetch rows from