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Re: UTF8MatchText

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, pgsql-patches(at)postgresql(dot)org
Subject: Re: UTF8MatchText
Date: 2007-05-17 14:20:50
Message-ID: 464C64C2.6000804@dunslane.net (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
Itagaki,

I find this still fairly unclean. It certainly took me some time to get 
me head around what's going on.

ISTM we should generate all these match functions from one body of code 
plus some #define magic.

As I understand it, we have three possible encoding switches:  Single 
Byte, UTF8 and other Multi Byte Charsets, and two possible case 
settings: case Sensitive and Case Insensitive. That would make for a 
total of six functions, but in the case of both UTF8 and other MBCS we 
don't need a special Case Insensitive function - instead we downcase 
both the string and the pattern and then use the Case Sensitive 
function. That leaves a total of four functions.

What is not clear to me is why the UTF8 optimisation work, and why it 
doesn't apply to other MBCS. At the very least we need a comment on that.

I also find the existing function naming convention somewhat annoying - 
having foo() and MB_foo() is less than clear. I'd rather have SB_foo() 
and MB_foo(). That's not your fault, of course.

If you supply me with some explanation on the UTF8 optimisation issue, 
I'll prepare a revised patch along these lines.

cheers

andrew



ITAGAKI Takahiro wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>
>   
>>> I do not understand this patch.  You have defined two functions,
>>> UTF8MatchText() and UTF8MatchTextIC(), and the difference between them
>>> is that one calls CHAREQ and the other calls ICHAREQ, but just above
>>> those two functions you define the macros identically:
>>>       
>> Why are there two functions?  Also, can't you use one function and just
>> pass a boolean to indicate whether case should be ignored?
>>     
>
> The same is true of MBMatchText() and MBMatchTextIC().
> Now, I'll split the patch into two changes.
>
> 1. DropMBMatchTextIC.patch
>         Drop MBMatchTextIC() and use MBMatchText() instead.
>
> 2. UTF8MatchText.patch
>         Add UTF8MatchText() as a specialized version of MBMatchText().
>
>
> As a future work, it might be good to research the performance of rewriting
> "col ILIKE 'pattern'" to "lower(col) LIKE lower('pattern')" in planner so that
> we can avoid to call lower() for constant pattern in the right-hand side and
> can use functional indexes (lower(col)). I think we never need MBMatchTextIC()
> in the future unless we move to wide-character server encoding :)
>
> Regards,
> ---
> ITAGAKI Takahiro
> NTT Open Source Software Center
>
>   
> ------------------------------------------------------------------------
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
>        choose an index scan if your joining column's datatypes do not
>        match
>   

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