ks_socket.c File Reference

libkarmaclient abstract socket type and documentation. More...

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Detailed Description

libkarmaclient abstract socket type and documentation.

This file contains documentation about socket implementations for libkarmaclient. Concrete socket implementations included with this library are found in ks_socket_posix.c.

Timeouts and the Karma Query Server

The karma server has an internal trigger (currently set at 2 seconds), after which it will respond with whatever data it has collected. So, when choosing timeout values, you must start with a timeout greater than the expected maximum network latency and finish with a value greater than the server timeout plus the expected maximum network latency. This means that there will be an early retry for a dropped packet, but if the query is complex, the client is guaranteed to wait "long enough" for a response.

We suggest starting with a timeout of 1 second, and treble it for 3 retries, to finish with a timeout of 9 seconds. See also ks_socket_ask().

Packet reordering

Responses are not ordered. The client must use query ids to match the responses up with the correct queries. It is usually necessary to use a client-side response cache to achieve this.

If you stream requests at high speed over a socket, the server may send responses back over a socket in a different order to order in which the requests were sent. This applies to both TCP and UDP modes.

If you wait for each response on a particular socket before sending the next query, then you can nearly lock-step the queries, but if a response is apparently "lost", it may still appear later, so this strategy is not totally reliable.

There is packet reordering code in ks_socket_posix.c which sorts this out. There is also a "simple version" (lines 570-591) in a comment which is a non-pthread explanation of the more complex code below.

Definition in file ks_socket.c.

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