Re: [squid-users] Q: http keepalives and time_wait sockets

Amos Jeffries wrote:
> Gaetano Giunta wrote:
>> Q1: Reading the archives of this mailing list, I concluded that squid
>> does not support using keep-alive in connections to source servers.
>>
>> I assume that setting keep-alive On on an Apache source server cached
>> by squid would thus be harmless: since squid does not do keepalives,
>> the connections would be terminated immediately - Apache would waste
>> time keeping processes busy waiting on sockets after squid terminated
>> its http/1.0 request.
>>
>> The advantage being that is the same apache server serves some other
>> site beside the one cached by squid, or if squid is disabled
>> temporarily, keepalives will be automatically in effect.
>>
>> Is this correct? Are there any advantages/drawbacks that are escaping
>> me?
>
> The conclusion that Squid does not support keepalive is incorrect.
> Note the default config setting.
> http://www.squid-cache.org/Doc/config/server_persistent_connections/
>
Sorry, I must have confused it with HTTP 1.1 (I was not fully aware of
HTTP 1.0 keep alives).

One more question about keepalives is then the following: is a keepalive
connection to the origin server only used for a single client, or can it
be used for requests coming from many different clients?
If the former, is the keeplaive connection to the origin server kept
open as long as the one with the client is?
In short: is there a recommendation about setting the keepalivetimeout /
maxkeepaliverequests parameters for a high traffic apache server proxied
by squid, where the squid cache hit rate is about 80%?
If the average webpage contains eg. 50 objects, with such a cache hit
rate a client requesting them all with keepalive would on average
generate requests for 10 objects to the origin server - but the requests
could be 'sparse' in time, for the client would spend some time in
between requesting/receiveing the objects that squid has in cache...

> Also, HTTP/1.0 protocol assumes that keepalive is off unless
> explicitly stated as provided. Thus Apache receiving HTTP/1.0 request
> without keepalive permitted will result in the Apache will terminate
> the connection or send back a reply explicitly requesting the proxy to
> do keepalive.
>
> When Squid closes any connection the far-end always receives a FIN or
> RST TCP message. They are not left hanging waiting for data.
>
>>
>> Q2: Using squid as reverse proxy, I have seen that a lot of sockets
>> (200 to 300) are always listed on the origin server, coming from the
>> squid server, in TIME_WAIT status.
>> Using netstat on the squid server itself at the same time, I see
>> about 10 open sockets, none of which in TIME_WAIT.
>> Is this normal? Is it a sign of some misconfiguration? (note: there
>> is probably a firewall currently sitting between the two servers).
>> Can it be related somehow to keepalives?
>
> Maybe yes, maybe no. More likely related to unknown-length objects
> with the server closing the connection after each send to signal
> end-of-object.
Interesting.
I suppose that files (images/css/js) always have a known length, that
would leave only requests for dynamically generated objects as possible
cause (or responses without bodies?).

Thanks for the quick answer
Gaetano

>
> TIME_WAIT only means that the sockets were previously used (even if
> closed properly) and are waiting the TCP timeout before safe re-use.
>
> Amos
Received on Mon Apr 19 2010 - 14:38:43 MDT