Re: default locale considered harmful? (was Re: [GENERAL]

Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > So, my understanding is that you would create something such as:
> >     CREATE INDEX iix ON tab (LIKE col)
> > and that does LIKE lookups and knows how to do col LIKE 'abc%', but it
> > can't be used for >= or ORDER BY, but it can be used for equality tests?
> 
> Hm.  Right at the moment, it wouldn't be used for equality tests unless
> you spelled equality as "a ~=~ b".  I wonder whether that's necessary
> though; couldn't we dispense with that operator and use ordinary
> equality as the BTEqual member of these opclasses?  Are there any
> locales that claim that not-physically-identical strings are equal?

Let me see if I understand.  

Our default indexes will be able to do =, >, <, ORDER BY, and the
special index will be able to do LIKE, ORDER BY, and maybe equals.  Do I
have that correct?

Looking at CVS, I see the warning about non-C locales has been removed. 
Should we instead mention the new LIKE index method?
# (Be sure to maintain the correspondence with locale_is_like_safe() in selfuncs.c.)if test x`pg_getlocale COLLATE` !=
xC&& test x`pg_getlocale COLLATE` != xPOSIX; then    echo "This locale setting will prevent the use of indexes for
patternmatching"    echo "operations.  If that is a concern, rerun $CMDNAME with the collation order"    echo "set to
\"C\". For more information see the Administrator's Guide."fi
 

Doing LIKE with single-byte encodings would be easy because it would be
only 256 compares to find the min/max char values, but that doesn't work
with multi-byte encodings, right?

This LIKE/encoding problem is a tricky one because it gives poor
performance with little warning to users.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
359-1001+  If your life is a hard drive,     |  13 Roberts Road +  Christ can be your backup.        |  Newtown Square,
Pennsylvania19073