Re: Patch for collation using ICU - Mailing list pgsql-hackers

Palle Girgensohn wrote:
> >
> > Is this patch ready for application?
> 
> I don't think so, not quite. I have not had any positive reports from linux 
> users, this is only tested in a FreeBSD environment. I'd say it needs some 
> more testing.

OK.

> Also, apparently, ICU is installed by default in many linux distributions, 
> and usually it is version 2.8. Some linux users have asked me if there are 
> plans for a patch that works with ICU 2.8. That's probably a good idea. IBM 
> and the ICU folks seem to consider 3.2 to be the stable version, older 
> versions are hard to find on their sites, but most linux distributers seem 
> to consider it too bleeding edge, even gentoo. I don't know why they don't 
> agree.

Good point.  Why would linux folks need ICU?  Doesn't their OS support
encodings natively?  I am particularly excited about this for OSs that
don't have such encodings, like UTF8 support for Win32.

Because ICU will not be used unless enabled by configure, it seems we
are fine with only supporting the newest version.  Do Linux users need
to use ICU for any reason?

> > I do have a few questions:
> >
> > Why don't you use the lc_ctype_is_c() part of this test?
> >
> >      if (pg_database_encoding_max_length() > 1 && !lc_ctype_is_c())
> 
> Um, well, I didn't think about that. :)  What would be the locale in this 
> case? c_C.UTF-8? ;)  Hmm, it is possible to have CTYPE=C and use a wide 
> encoding, indeed. Then the strings will be handled like byte-wide chars. 
> Yeah, it's a bug. I'll fix it! Thanks.

The additional test is more of an optmization, and it fixes a problem
with some OSs that have processing problems with UTF8 when the locale is
supposed to be turned off, like in "C".  I realize ICU might be fine
with it but the optimization still is an issue.

> > Why is so much code added, for example, in lower()?  The existing
> > multibyte code is much smaller, and lots of code is added in other
> > places too.
> 
> ICU uses UTF-16 internally, so all strings must be converted from the 
> database encoding to UTF-16. Since that means the strings need to be 
> copied, I took the same approach as in varlena.c:varstr_cmp(), where small 
> strings use the heap and only larger strings use a palloc. Comments in 
> varstr_cmp about performance made me use that approach.

Oh, interesting.   I think you need to create new functions that
factor out that common code so the patch is smaller and easier to
maintain.

> Also, in the latest patch, I also added checks and logging for *every* 
> status returned from ICU. I hope this will help debugging on debian, where 
> previous version didn't work. That excessive status checking is hardly be 
> necessary once the stuff is better tested.
> 
> I think the string copying and heap/palloc choices stands for most of the 
> code bloat, together with the excessive status checking and logging.

OK, move that into some common functions and I think it will be better.

> > Why do you need to add a mapping of encoding names from iana to our
> > names?
> 
> This was already answered by John Hansen... There's an old thread here 
> about the choice of the name "UNICODE" to describe an encoding, which it 
> doesn't. There's half a dozen unicode based encodings... UTF-8 is used by 
> postgresql, that would have been a better name... Similarly for most other 
> encodings, really. ICU expect a setlocale(3) string (i.e. IANA). PostgreSQL 
> can't provide it, so a mapping table is required.

We have depricated UNICODE in 8.1 in favor of UTF8 (no dash).  Does that
help?

> I use this patch in production on one FreeBSD 4.10 server at the moment. 
> With the latest version, I've had no problems. Logging is swithed on for 
> now, and it shows no signs of ICU complaining. I'd like more reports on 
> Linux, though.

OK, I certainly would like this all done for 8.1 which should have
feature freeze on July 1.

--  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