On 07/22/2013 12:49 PM, Greg Stark wrote:
On Mon, Jul 22, 2013 at 12:50 PM, Peter Eisentraut <pete...@gmx.net> wrote:
I think part of the problem is that we call strcoll for each comparison,
instead of doing strxfrm once for each datum and then just strcmp for
each comparison. That is effectively equivalent to what the proposal
implements.
Fwiw I used to be a big proponent of using strxfrm. But upon further
analysis I realized it was a real difficult tradeoff. strxrfm saves
potentially a lot of cpu cost but at the expense of expanding the size
of the sort key. If the sort spills to disk or even if it's just
memory bandwidth limited it might actually be slower than doing the
additional cpu work of calling strcoll.
It's hard to see how to decide in advance which way will be faster. I
suspect strxfrm is still the better bet, especially for complex large
character set based locales like Chinese. strcoll might still win by a
large margin on simple mostly-ascii character sets.
Perhaps we need a bit of performance testing to prove the point.
Maybe the behaviour should be locale-dependent.
cheers
andrew
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