Sending result sets from backend to frontend is _slow_

Glen Parker (glenebob(at)nwlink(dot)com) reports a bug with a severity of 2
The lower the number the more severe it is.

Short Description
Sending result sets from backend to frontend is _slow_

Long Description
When operating over a fast network (ethernet), the sending of select result rows from the backend is very slow, ie. it uses only a small fraction of available network bandwidth. I am running postgres 7.0.2 on a Redhat 6.1 install on x86, and using the postodbc driver on win2k, and I have looked at the odbc driver code until I am blue in the face :-) and I am confident that it is doing the right thing with network IO (large read buffers, 4096 bytes by default). There is also very low CPU utilization on both machines during large result transfers. From this, I believe the problem is in the backend, and I think it is probably sending one row per network write. Obviously, if this is the case, it almost guarantees sub-optimal network performance on fast networks, except on very wide result sets.
The backend code is quite difficult to dig into for a beginner, but if someone could explain briefly how results are sent, and some pointers on where I might start, I would be able to at least attempt a fix for it. Or one of the gurus could look into it :-)

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