javascript - how to get users online status jsp -

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i want web application users logged list possible flows unexpected shutdown (power cut), force closed browser , whatever in flow. want show online users status text. find solutions but,they solutions take server lot of memory update login table last_logged column current time every 20 seconds client side server side , check last_logged time less 20 seconds takes status offline. need perfect solution out heavy work load server. simply, want gmail chat list flows working fine on gmail chat. don't know these concept new concept. may find solution if know solution type of concept please share knowledge. it, must helpful developers , appreciate effect.

thanks spending valuable time reading post :)

why think updating table takes "a lot of memory"? or why think "heavy work load server"? nothing. there no solution other using database described, because browsers don't implement kind of messages when user leaves site. you've got track updating table last access time , on.

and if browsers did implement "user has left site" type messages, still have update database , read 1 track stuff.

plus, if browsers sent these kinds of message, if user lost power, browser not able send it.


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