Question

I’m working currently on a long polling script where i’ve to check a database for new changes.

I’m wondering if it will be too much resources consuming to do the query in a while loop then do the query again without any delay, or if i should let a little delay like one second.

When I look on Facebook for example it seems to have the new changes within the second so i guess they they don’t have any delay while checking the database or this delay is really short like half a second.

I don’t expect a straight answer but more advises on the best practices for this

Thanks

Answer 1

Yeah, if the while loop runs as fast as it can (it will) you will not just get a fast rate which might overwhelm the database connection, but you’ll also not get a very ‘even’ rate of polling.

Try something like

$polllength = 1;
while(1) {
    $polltime = microtime(true);
    //poll function call;
    $endtime = microtime(true);
    $sleeptime = $polllength - ($endtime-$polltime);
    sleep($sleeptime);
}

This way your polls are about $polllength seconds apart no matter how the polling function varies (it will due to INTARNETS)

EDIT: also, make sure there’s a way out of that while loop but everyone should know that y’all

For load balancing, you want to be able to tweak the polllength value somehow, so as to not be completely hardcoded. Whether it be in a configuration file or whatnot is up to you, it might even be a value that increases as load increases. That’s up to how it actually ‘feels’ to the end user and how the server is really faring. A good rule of thumb is that n threads max means n * (poll length / avg response time) users. Reaching beyond that limit would doubtlessly increase response times as the users wait for responses from the overwhelmed server.