Dennis Bjorklund wrote:
> Tom Lane skrev:
>> You could imagine trying to do
>> % a byte at a time (and indeed that's what I'd been thinking it did)
>> but that gets you out of sync which breaks the _ case.
>
> It is only when you have a pattern like '%_' when this is a problem
> and we could detect this and do byte by byte when it's not. Now we
> check (*p == '\\') || (*p == '_') in each iteration when we scan over
> characters for '%', and we could do it once and have different loops
> for the two cases.
>
> Other than this part that I think can be optimized I don't see
> anything wrong with the idea behind the patch. To make the '%' case
> fast might be an important optimization for a lot of use cases. It's
> not uncommon that '%' matches a bigger part of the string than the
> rest of the pattern.
>
Are you sure? The big remaining char-matching bottleneck will surely be
in the code that scans for a place to start matching a %. But that's
exactly where we can't use byte matching for cases where the charset
might include AB and BA as characters - the pattern might contain %BA
and the string AB. However, this isn't a danger for UTF8, which leads me
to think that we do indeed need a special case for UTF8, but for a
different improvement from that proposed in the original patch. I'll
post an updated patch shortly.
cheers
andrew
