Re: not exactly a bug report, but surprising behaviour

Greg Stark <gsstark(at)mit(dot)edu> writes:
> I'm watching this query I'm working on now drive the cpu to 100% for 6+ hours
> with virtually no I/O. And I think it's the best I can do. All the times is
> being spent moving bits around from one place to another.

It would be interesting to see a gprof profile of that.

> It occurs to me that it's possible postgres is doing this already at a lower
> level of abstraction.

Yes, tuplesort.c has heard of pushing pointers around rather than
copying records. I wonder though whether data is being pushed out to
kernel disk buffers and then back in again --- do you have sort_mem
set large enough? Another likely theory is that the interface layers
needed to access datatype-specific comparison routines are chewing the
cycles. Need facts not speculation to know where the bottleneck is...

regards, tom lane