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Support C.UTF-8 locale in the new builtin collation provider.

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The builtin C.UTF-8 locale has similar semantics to the libc locale of
the same name. That is, code point sort order (fast, memcmp-based)
combined with Unicode semantics for character operations such as
pattern matching, regular expressions, and
LOWER()/INITCAP()/UPPER(). The character semantics are based on
Unicode simple case mappings.

The builtin provider's C.UTF-8 offers several important advantages
over libc:

 * faster sorting -- benefits from additional optimizations such as
   abbreviated keys and varstrfastcmp_c
 * faster case conversion, e.g. LOWER(), at least compared with some
   libc implementations
 * available on all platforms with identical semantics, and the
   semantics are stable, testable, and documentable within a given
   Postgres major version

Being based on memcmp, the builtin C.UTF-8 locale does not offer
natural language sort order. But it is an improvement for most use
cases that might otherwise use libc's "C.UTF-8" locale, as well as
many use cases that use libc's "C" locale.

Discussion: https://postgr.es/m/ff4c2f2f9c8fc7ca27c1c24ae37ecaeaeaff6b53.camel%40j-davis.com
Reviewed-by: Daniel Vérité, Peter Eisentraut, Jeremy Schneider
This commit is contained in:
Jeff Davis
2024-03-19 15:24:41 -07:00
parent fd0398fcb0
commit f69319f2f1
17 changed files with 494 additions and 26 deletions
Download Patch File Download Diff File Expand all files Collapse all files

52
src/backend/utils/adt/pg_locale.c
View File

@@ -1270,8 +1270,14 @@ lookup_collation_cache(Oid collation, bool set_flags)
if (collform->collprovider == COLLPROVIDER_BUILTIN)
{
Datum datum;
const char *colllocale;
datum = SysCacheGetAttrNotNull(COLLOID, tp, Anum_pg_collation_colllocale);
colllocale = TextDatumGetCString(datum);
cache_entry->collate_is_c = true;
cache_entry->ctype_is_c = true;
cache_entry->ctype_is_c = (strcmp(colllocale, "C") == 0);
}
else if (collform->collprovider == COLLPROVIDER_LIBC)
{
@@ -1670,7 +1676,6 @@ pg_newlocale_from_collation(Oid collid)
collversionstr = TextDatumGetCString(datum);
Assert(collform->collprovider != COLLPROVIDER_BUILTIN);
if (collform->collprovider == COLLPROVIDER_LIBC)
datum = SysCacheGetAttrNotNull(COLLOID, tp, Anum_pg_collation_collcollate);
else
@@ -1725,7 +1730,13 @@ get_collation_actual_version(char collprovider, const char *collcollate)
{
char *collversion = NULL;
/* the builtin collation provider is not versioned */
/*
* The only two supported locales (C and C.UTF-8) are both based on memcmp
* and are not expected to change.
*
* Note that the character semantics may change for some locales, but the
* collation version only tracks changes to sort order.
*/
if (collprovider == COLLPROVIDER_BUILTIN)
return NULL;
@@ -2505,13 +2516,17 @@ pg_strnxfrm_prefix(char *dest, size_t destsize, const char *src,
int
builtin_locale_encoding(const char *locale)
{
if (strcmp(locale, "C") != 0)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("invalid locale name \"%s\" for builtin provider",
locale)));
if (strcmp(locale, "C") == 0)
return -1;
if (strcmp(locale, "C.UTF-8") == 0)
return PG_UTF8;
return -1;
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("invalid locale name \"%s\" for builtin provider",
locale)));
return 0; /* keep compiler quiet */
}
@@ -2525,13 +2540,28 @@ builtin_locale_encoding(const char *locale)
const char *
builtin_validate_locale(int encoding, const char *locale)
{
if (strcmp(locale, "C") != 0)
const char *canonical_name = NULL;
int required_encoding;
if (strcmp(locale, "C") == 0)
canonical_name = "C";
else if (strcmp(locale, "C.UTF-8") == 0 || strcmp(locale, "C.UTF8") == 0)
canonical_name = "C.UTF-8";
if (!canonical_name)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("invalid locale name \"%s\" for builtin provider",
locale)));
return "C";
required_encoding = builtin_locale_encoding(canonical_name);
if (required_encoding >= 0 && encoding != required_encoding)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("encoding \"%s\" does not match locale \"%s\"",
pg_encoding_to_char(encoding), locale)));
return canonical_name;
}