On 08/25/2014 06:14 PM, Tom Lane wrote:
Heikki Linnakangas <hlinnakan...@vmware.com> writes:
On 08/25/2014 04:48 PM, Tom Lane wrote:
[ scratches head... ]  Surely similar_escape is marked immutable, and
will therefore be executed exactly once in either of these formulations,
because the planner will fold the expression to a constant.

Yeah, just noticed that myself..

... although, given that, it is also fair to wonder how much the speed of
similar_escape really matters.  Surely in most use-cases the pattern and
escape char will be constants.  And, when they are not, wouldn't the
subsequent parsing work for the regexes dominate the cost of
similar_escape anyway?

IOW, I'm not sure we should be advising Jeff to duplicate code in
order to have a fast path.  Keeping it short might be the best goal.

It's certainly not worth bending over backwards for a small performance gain here, but I think special-casing a single-byte escape sequence is still quite reasonable. It doesn't make the code any longer.

- Heikki

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