CODEWITHSUNDEEP
pythonperformancesocketsnetwork-programmingbuffer
Alexei Tenitski
Alexei Tenitski

Reputation: 9370

Speeding up socket send behavior (in Python)

I have a script which sends 5-10 requests a second to the server. The most crucial requirement i have is a limit of requests per second. It must always be the specific figure, not more and no less. To do it i send requests after a given interval of time (minus time required to send previous request).

Problem: some requests are sent fast enough however others take too much time at sock.sendall() step. I believe this is because send buffer is full and execution is blocked until buffer is cleared.

What can i do to flush that buffer quicker?

One of the options i tried is to disable Nagle:

sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)

but it didn't seem to improve things.

Another option which even sounds too wrong to try it is to set send buffer to the length of the request before each sendall() call.

Is there anything i can do to get more predictable requests per second?

One more option i just thought about: have several processes which will do a small amount of requests per second each, hopefully it will make results more predictable.

OS in question is Centos.

Update: It seems that my error in setting socket options after connect. Looks like size buffer can only be set prior connect() call. Same with TCP_NODELAY. Haven't yet had time to test if it makes any difference.

Upvotes: 1

Views: 2495

Answers (2)

Alexei Tenitski
Alexei Tenitski

Reputation: 9370

(From How can I force a socket to send the data in its buffer?)

You can't force it. Period. TCP makes up its own mind as to when it can send data. Now, normally when you call write() on a TCP socket, TCP will indeed send a segment, but there's no guarantee and no way to force this. There are lots of reasons why TCP will not send a segment: a closed window and the Nagle algorithm are two things to come immediately to mind.

Read the full post, it is quite in-depth and clarified some of the things for me eg when disabling Nagle algorithm makes sense and so on.

Upvotes: 0

user207421
user207421

Reputation: 311048

The most crucial requirement i have is a limit of requests per second. It must always be the specific figure, not more and no less.

That requirement is completely unimplementable via TCP. You would also need real-time guarantees of service times at the peer.

Upvotes: 2

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