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 <daniel@manitou-mail.org>
Reviewed-by: Peter Geoghegan <pg@bowt.ie>
Discussion: https://www.postgresql.org/message-id/flat/1ccc668f-4cbc-0bef-af67-450b47cdfee7@2ndquadrant.com

2 files changed, 2 insertions, 1 deletions

diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h
index 3bbdb5e2f7..b093a3c8ac 100644
--- a/src/include/optimizer/planmain.h
+++ b/src/include/optimizer/planmain.h
@@ -53,7 +53,7 @@ extern bool is_projection_capable_plan(Plan *plan);
 extern Sort *make_sort_from_sortclauses(List *sortcls, Plan *lefttree);
 extern Agg *make_agg(List *tlist, List *qual,
 		 AggStrategy aggstrategy, AggSplit aggsplit,
-		 int numGroupCols, AttrNumber *grpColIdx, Oid *grpOperators,
+		 int numGroupCols, AttrNumber *grpColIdx, Oid *grpOperators, Oid *grpCollations,
 		 List *groupingSets, List *chain,
 		 double dNumGroups, Plan *lefttree);
 extern Limit *make_limit(Plan *lefttree, Node *limitOffset, Node *limitCount);
diff --git a/src/include/optimizer/tlist.h b/src/include/optimizer/tlist.h
index 58db79203b..46d614f4fb 100644
--- a/src/include/optimizer/tlist.h
+++ b/src/include/optimizer/tlist.h
@@ -32,6 +32,7 @@ extern bool tlist_same_collations(List *tlist, List *colCollations, bool junkOK)
 extern void apply_tlist_labeling(List *dest_tlist, List *src_tlist);
 
 extern Oid *extract_grouping_ops(List *groupClause);
+extern Oid *extract_grouping_collations(List *groupClause, List *tlist);
 extern AttrNumber *extract_grouping_cols(List *groupClause, List *tlist);
 extern bool grouping_is_sortable(List *groupClause);
 extern bool grouping_is_hashable(List *groupClause);