Collations with nondeterministic comparison

This adds a flag "deterministic" to collations.  If that is false,
such a collation disables various optimizations that assume that
strings are equal only if they are byte-wise equal.  That then allows
use cases such as case-insensitive or accent-insensitive comparisons
or handling of strings with different Unicode normal forms.

This functionality is only supported with the ICU provider.  At least
glibc doesn't appear to have any locales that work in a
nondeterministic way, so it's not worth supporting this for the libc
provider.

The term "deterministic comparison" in this context is from Unicode
Technical Standard #10
(https://unicode.org/reports/tr10/#Deterministic_Comparison).

This patch makes changes in three areas:

- CREATE COLLATION DDL changes and system catalog changes to support
  this new flag.

- Many executor nodes and auxiliary code are extended to track
  collations.  Previously, this code would just throw away collation
  information, because the eventually-called user-defined functions
  didn't use it since they only cared about equality, which didn't
  need collation information.

- String data type functions that do equality comparisons and hashing
  are changed to take the (non-)deterministic flag into account.  For
  comparison, this just means skipping various shortcuts and tie
  breakers that use byte-wise comparison.  For hashing, we first need
  to convert the input string to a canonical "sort key" using the ICU
  analogue of strxfrm().

Reviewed-by: Daniel Verite <[email protected]>
Reviewed-by: Peter Geoghegan <[email protected]>
Discussion: https://www.postgresql.org/message-id/flat/[email protected]

1 files changed, 15 insertions, 17 deletions

diff --git a/src/backend/utils/adt/name.c b/src/backend/utils/adt/name.c
index 3a7887d4553..54425925edb 100644
--- a/src/backend/utils/adt/name.c
+++ b/src/backend/utils/adt/name.c
@@ -131,14 +131,26 @@ namesend(PG_FUNCTION_ARGS)
  * have a '\0' terminator.  Whatever might be past the terminator is not
  * considered relevant to comparisons.
  */
+static int
+namecmp(Name arg1, Name arg2, Oid collid)
+{
+	/* Fast path for common case used in system catalogs */
+	if (collid == C_COLLATION_OID)
+		return strncmp(NameStr(*arg1), NameStr(*arg2), NAMEDATALEN);
+
+	/* Else rely on the varstr infrastructure */
+	return varstr_cmp(NameStr(*arg1), strlen(NameStr(*arg1)),
+					  NameStr(*arg2), strlen(NameStr(*arg2)),
+					  collid);
+}
+
 Datum
 nameeq(PG_FUNCTION_ARGS)
 {
 	Name		arg1 = PG_GETARG_NAME(0);
 	Name		arg2 = PG_GETARG_NAME(1);
 
-	/* Collation doesn't matter: equal only if bitwise-equal */
-	PG_RETURN_BOOL(strncmp(NameStr(*arg1), NameStr(*arg2), NAMEDATALEN) == 0);
+	PG_RETURN_BOOL(namecmp(arg1, arg2, PG_GET_COLLATION()) == 0);
 }
 
 Datum
@@ -147,21 +159,7 @@ namene(PG_FUNCTION_ARGS)
 	Name		arg1 = PG_GETARG_NAME(0);
 	Name		arg2 = PG_GETARG_NAME(1);
 
-	/* Collation doesn't matter: equal only if bitwise-equal */
-	PG_RETURN_BOOL(strncmp(NameStr(*arg1), NameStr(*arg2), NAMEDATALEN) != 0);
-}
-
-static int
-namecmp(Name arg1, Name arg2, Oid collid)
-{
-	/* Fast path for common case used in system catalogs */
-	if (collid == C_COLLATION_OID)
-		return strncmp(NameStr(*arg1), NameStr(*arg2), NAMEDATALEN);
-
-	/* Else rely on the varstr infrastructure */
-	return varstr_cmp(NameStr(*arg1), strlen(NameStr(*arg1)),
-					  NameStr(*arg2), strlen(NameStr(*arg2)),
-					  collid);
+	PG_RETURN_BOOL(namecmp(arg1, arg2, PG_GET_COLLATION()) != 0);
 }
 
 Datum