I'm creating a service with php that returns json data from a table that contains 2100 rows. I'm using the following setup in dev:
My guess would be memory limitations (the children are being killed by the server). You can increase it but it won't solve the issue - what happens when you have 1 million records?
My advise is that you implement a pagination params and a max number of records to return:
http://website.com/api/v1/getUsers?position=0 http://website.com/api/v1/getUsers?position=100 http://website.com/api/v1/getUsers?position=200 etc..
This will drastically lower the stress on your system and enable the users to also lower their throughput in the event they only want the top x records, last 2, etc..
If you still want to be able to serve all, you can check this thread out to learn how to increase the memory for Apache: http://stackoverflow.com/a/36920556/1935500