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Re: [HELP] What's the underlying connection reusing policy, can it be RR
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From: Daniel Stenberg via curl-library <curl-library_at_lists.haxx.se>
Date: Wed, 19 Jan 2022 11:03:04 +0100 (CET)
On Wed, 19 Jan 2022, 白水月 via curl-library wrote:
I don't quite understand what you want to accomplish.
The connection pool libcurl maintains is there to enable repeated requests
to the same hosts to reuse connections.
If you don't do repeated requests, like if the requests are done with so long
interval that the connections are closed by the server before they are used
again, then maybe just let that happen?
> 4. As time pass by, some underlying TCP connection was close by the server.
> The periodic keepalive request fail to save the underlying TCP connection
> due to libcurl will reuse existing connection, which leads to one
> connection(in this case) never send keepalive request to server.
For most use cases it is most efficient to pick the most recently used
connection for reuse (and not round-robin) - quite simply for better success
rate. The longer a connection has been left idle, the bigger the risk that it
doesn't work anymore.
> Another "easy" approach is if we can set the resuse policy of existing
> connections to Round Robin, it seems everything goes well. But I fail to
> find out any stuff about the reusing policy. Is it possible to do this? And
> what's best practise for the scenario that I faced?
There's no such option available and I can't think of any proper way for an
application to trick libcurl into behaving like this.
If the connections are created at different times, there is
CURLOPT_MAXLIFETIME_CONN that can make libcurl stop considering a connection
for reuse once it has reached a certain age, but that doesn't seem to be very
helpful for your case.
Date: Wed, 19 Jan 2022 11:03:04 +0100 (CET)
On Wed, 19 Jan 2022, 白水月 via curl-library wrote:
I don't quite understand what you want to accomplish.
The connection pool libcurl maintains is there to enable repeated requests
to the same hosts to reuse connections.
If you don't do repeated requests, like if the requests are done with so long
interval that the connections are closed by the server before they are used
again, then maybe just let that happen?
> 4. As time pass by, some underlying TCP connection was close by the server.
> The periodic keepalive request fail to save the underlying TCP connection
> due to libcurl will reuse existing connection, which leads to one
> connection(in this case) never send keepalive request to server.
For most use cases it is most efficient to pick the most recently used
connection for reuse (and not round-robin) - quite simply for better success
rate. The longer a connection has been left idle, the bigger the risk that it
doesn't work anymore.
> Another "easy" approach is if we can set the resuse policy of existing
> connections to Round Robin, it seems everything goes well. But I fail to
> find out any stuff about the reusing policy. Is it possible to do this? And
> what's best practise for the scenario that I faced?
There's no such option available and I can't think of any proper way for an
application to trick libcurl into behaving like this.
If the connections are created at different times, there is
CURLOPT_MAXLIFETIME_CONN that can make libcurl stop considering a connection
for reuse once it has reached a certain age, but that doesn't seem to be very
helpful for your case.
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