How fast does tcp_tw_recycle mean?

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We use the TCP short connection to connect to server. When the web view is too high, many TIME_WAIT tcp connections cause system can not establish new connection.

I searched some information in Web, and I found many people recommended to set tcp_tw_recycle to 1.

The Linux official document explains this option as follows:
tcp_tw_recycle - BOOLEAN
Enable fast recycling TIME-WAIT sockets. Default value is 0.
It should not be changed without advice/request of technical
experts.

This explanation is not specific. I have the following two questions:
1) How fast? 1 min, 1 sec or others?
2) what does the warning "It should not be changed without advice/request of technical
experts." imply ?

Posted 23-Oct-12 22:25pm

WebMaster

Updated 23-Oct-12 22:30pm

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Richard MacCutchan · Answer 1 · 2012-10-23T22:35:00

Solution 1

There seems very little documentation or user experiences of this value but the bottom line seems to be:

No idea; look at the Linux source code.
Don't do it.

The warning against use suggests that it may have other side effects but no one seems to know what they may be.

Posted 23-Oct-12 22:35pm

Richard MacCutchan

Comments

[no name] 24-Oct-12 4:56am

Thanks for your comment though it is not the final solution :)

Richard MacCutchan 24-Oct-12 5:06am

Looking at the Google search finds I get the feeling there is not a full or useful answer around.

[no name] 24-Oct-12 5:15am

me too :)

markkuk 24-Oct-12 7:41am

The "side effects" involve load balancers, stateful firewalls or other network devices that track TCP connection states. They may get confused and drop packets if sockets get reused too early.

Richard MacCutchan 24-Oct-12 7:58am

So I think the advice "It should not be changed without advice/request of technical experts." should just read "It should not be changed".

markkuk · Answer 2 · 2012-10-24T01:43:00

Solution 2

Try tcp_tw_reuse=1 instead, it's generally considered safer. See here[^] for more details.

Posted 24-Oct-12 1:43am

markkuk

Comments

[no name] 24-Oct-12 21:55pm

Thanks. tcp_tw_reuse may be better choice.