well, obviously with a heavy traffic site this solution is much less than
ideal. i was thinking more along the lines of a very low traffic site
(small intranets, for instance) where you REALLY WANT TO KNOW when that
client's machine and/or browser goes down. even without the massive network
load the processing load on the server is going to be insane trying to track
and determine time outs for thousands or tens of thousands of connections...
also there's no reason the heartbeat has to be that fast or even has to be a
heartbeat at all. a simpler approach is that when a session is invalidated
on the server due to timeout you could "ping" the applet on the client to
see if the user is there, but sleeping. if no response, throw the session
away and forget about it. if the user is still staring at the page (i.e.,
the applet is still around) then perhaps you want to hold onto that session
a little longer. this minimizes the traffic to (N*1000)/T (where T is the
time-out interval, probably something >= 30 seconds). this frees the server
up from having to count how long it's been since user X (of N*1000) sent in
a heartbeat and adds only 1 transaction per user per time-out interval
(worst case - that assumes all of your users suddenly fell asleep).
better? worse? am i totally off track? (wouldn't be the first time, won't
be the last). :)
................ron.
-----Original Message-----
From: Preston L. Bannister <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Saturday, December 04, 1999 2:52 PM
Subject: Re: [Session tracking]
>Also note that heartbeats scale very poorly. I expect large numbers of
low-activity users. Say the number of "connected" users is:
>
> N*1000
>
>Then the number of heartbeats with one every 5 seconds is:
>
> N*1000/5 => N*200 per second
>
>So I can expect N*200 requests per second when absolutely nothing is
happening.
>
>This is not a particularly good design...
>
>> -----Original Message-----
>> From: A mailing list for discussion about Sun Microsystem's Java Servlet
>> API Technology. [mailto:[EMAIL PROTECTED]]On Behalf Of Chris
>> Pratt
>> Sent: Saturday, December 04, 1999 1:34 PM
>> To: [EMAIL PROTECTED]
>> Subject: Re: [Session tracking]
>>
>>
>> So what you're saying is that if you use a heartbeat of about 5 seconds
(so
>> you don't overload your network with heartbeats) and then allow the user
to
>> miss, oh let's say 6 heartbeats just for the sake of argument to make
sure
>> it's not the insanely heavy network traffic that's in the way, your user
>> will be marked as go 30 seconds after his last confirmed heartbeat.
Seems
>> like I have the same time lag and I didn't have to do any extra
programming
>> to achieve it. =8^)
>> (*Chris*)
>>
>> ----- Original Message -----
>> From: "Ron Reynolds" <[EMAIL PROTECTED]>
>> To: <[EMAIL PROTECTED]>
>> Sent: Saturday, December 04, 1999 6:32 AM
>> Subject: Re: [Session tracking]
>>
>>
>> > a heart-beat would do it. if, after x seconds, you don't receive a
>> > heartbeat from your applet you can assume either (a) insanely heavy
>> network
>> > traffic, (b) client machine is unbelievably bogged down to a point
where
>> the
>> > applet can't get a time slice, or (c) the client machine is dead and/or
>> > disconnected from the network. combine that with simple ping and you
can
>> > even determine the difference between the browser being off and the
>> computer
>> > being off (again, assuming a stable, non-flooded network). (the other
>> way,
>> > even without power failures, is to terminate the browser process
>> directly).
>> > ................ron.
>
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