# [web] Firefox users who "tune" their browsers

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markr    1692
Hi all, A lot of Firefox users see pages like this and think that it's a really good idea to increase things like
network.http.max-persistent-connections-per-server to 8 or more

in about:config The problem is, that this value defaults to 2 for a good reason. It's because the W3C recommended that value to have minimal negative impact on server performance "for the greater good". MSIE and other browsers also respect this ethic, that creating large numbers of persistent connections is generally a bad thing (may be tunable in IE too, but not so easily). So it seems to me, that the users doing this "tuning" are trying to be greedy by getting more for themselves at the expense of other net users. Moreover, most articles which suggest these "optimisations" make no mention of this. Mark

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paulecoyote    1065
If it bothers admins of webservers it is possible to ensure that only 2 connections come from a specific destination from the server side - subsequent connection attempts are refused.

You can tune IE via a registry poke to have more then 2 connections, in fact there is an msdn article about it.

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DaBono    1496
I agree that setting your browser to more than 8 persisten connections is useless and not very social behaviour.

Looking at it the other way, the W3C recommended this probably way before web servers were stacked with RAM. Nowadays, also, CSS-scripts and favicon.ico's increased the number of requests per page, since every page nowadays contains tons of graphics.

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The fun thing about persistent connections is -- as the name suggests -- that they persist. There's a difference between just using a TCP stream just for one object, i.e. an image, and keeping that stream open for further requests to reduce the nontrivial overhead TCP has when opening a connection. Using a higher number of parallel but short-lived connections is not so big an issue, and even less one if you consider the hardware TCP offload engines that are more and more common. However, there's a maximum of connections somewhere inside the server's socket implementation, and if each client soaks up a number of those the server will not be able to answer more connection requests sooner or later, just because some idiots' browsers are idling on all the sockets.

Server performance might be affected because operations like select() are becoming more expensive with a bigger number of sockets to handle.

(Quick edit:) Also note that there are several options in Firefox that relate to the number of connections, here with the defaults as they are set on my system:

network.http.max-connections (24)
network.http.max-connections-per-server (8)
network.http.max-persistent-connections-per-proxy (4)
network.http.max-persistent-connections-per-server (2)