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Re: UTF8MatchText

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: Dennis Bjorklund <db(at)zigo(dot)dhs(dot)org>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, Bruce Momjian <bruce(at)momjian(dot)us>, pgsql-patches(at)postgresql(dot)org
Subject: Re: UTF8MatchText
Date: 2007-05-20 14:11:16
Message-ID: 46505704.8040203@dunslane.net (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches

I wrote:
>
>
>>
>> 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.
>

Here is a patch that implements this. Please analyse for possible breakage.

cheers

andrew



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