Show real time data to users with same response time - php

Question

I've doubt regarding speed and latency for show real time data.
Let's assume that I want to show read time data to users by fire ajax requests at every second that get data from MySql table by simple collection query.
For that currently these two options are bubbling in my mind
MySql / Amazon Aurora
File system
Among these options which would be better? Or any other solution?
As I checked practically, if we open one page in browser then ajax requests gives response in less than 500ms using PHP, MySql, Nginx stack.
But if we open more pages then same ajax requests gives response in more than 1 second that should be less than 500ms for every visitors.
So in this case if visitors increase then ajax requests gives very poor response.
I also checked with Node.js+MySql but same result.
Is it good to create json files for records and fetch data from file? Or any other solution?

Answer 1

Indeed, you have to use database to store actual data but you can easily add memory cache (it could be internal dictionary or separate component) to track actual updates.
Than your typical ajax request will look something like:
Memcache, do we have anything new for user 123?
Last update was 10 minutes ago
aha, so nothing new, let's return null;
When you write data:
Put data into database
Update lastupdated time for clients in memcache
Actual key might be different - e.g. chat room id. Idea is to read database only when updates actually happened.
Level 2:
You will burn you webserver and also client internet with high number of calls. You can do something:
DateTime start = DateTime.Now;
while(Now.Subtract(30 seconds) < start)
{
if (hasUpdates) return updates;
sleep(100);
}
Than client will call server 1 time per 30 seconds.
Client will get response immediately when server notices new data.