Seekable sockets: a mechanism to reduce copy overheads in TCP-based messaging

This paper extends the traditional socket interface to TCP/IP communication with the ability to seek rather than simply receive data in order. Seeking on a TCP socket allows a user program to receive data without first receiving all previous data on the connection. Through repeated use of seeking, a messaging application or library can treat a TCP socket as a list of messages with the potential to receive and remove data from any arbitrary point rather than simply the head of the socket buffer. Seeking facilitates copy-avoidance between a messaging library and user code by eliminating the need to first copy unwanted data into a library buffer before receiving desired data that appears later in the socket buffer. The seekable sockets interface is implemented in the Linux 2.6.13 kernel. Experimental results are gathered using a simple microbenchmark that receives data out-of-order from a given socket, yielding up to a 40% reduction in processing time. The code for seekable sockets is now available for patching into existing Linux kernels and for further development into messaging libraries