StackOverflow2013

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copied!<p>I have added a chat capability to a site using jquery and PHP and it seems to generally work well, but I am worried about scalability. I wonder if anyone has some advice. The key area for me I think is efficiently managing awareness of who is onine.</p> <p>detail: I haven't implemented long-polling (yet) and I'm worried about the raw number of long-running processes in PHP (Apache) getting out of control.</p> <p>My code runs a periodic jquery ajax poll (4secs), that first updates the db to say I am active and sets a timestamp. Then there is a routine that checks the timestamp for all active users and sets those outside (10mins) to inactive. This is fairly normal from my research so far. However, I am concenred that if I allow every active user to check every other active user and then everyone update the db to kick off inactive users, then I will get duplicated effort, record locks and unnecessary server load. </p> <p>So I have implemented an idea of the role of a 'sweeper'. This is just one of the online users, who inherits the role of the person doing the cleanup. Everyone else just checks whether there is a 'sweeper' in existence (DB read) and carries on. If there is no sweeper when they check, they make themselves sweeper (DB write for their own record). If there are more than one, make yourself 'non-sweeper', sleep for a random period and check again.</p> <p>My theory is that this way there is only one user regularly writing updates to several records on the relevant table and everyone else is either reading or just writing to their own record. So it works OK, but the problem possibly is that the process requires a few DB reads and may actually be less efficient than just letting everyone do the cleanup as with other research as I mentioned.</p> <p>I have had over 100 concurrent users running OK so far, but the client wants to scale up to several 100's, even over 1,000 and I have no idea of knowing at this stage whether this idea is good or not.</p> <p>Does anyone know whether this is a good approach or not, whether it is scalable to hundreds of active users, or whether you can recommend a different approach?</p> <p>AS an aside, long polling / comet for the actual chat messages seems simple and I have found a good resource for the code, but there are several blog comments that suggest it's dangerous with PHP and apache specifically. active threads etc. Impact minimsed with usleep and session_write_close. </p> <p>Again does anyone have any practical experience of a PHP long polling set up for hundreds of active users, maybe you can put my mind at ease ! Do I really ahve to look to migrate this to node.js (no experience) ?</p> <p>Thank you in advance </p> <p>Tony</p>

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