From a6bd28beb0639d4cf424e961862a65c466ca65bf Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 10 Aug 2021 18:10:29 -0400
Subject: [PATCH] Fix failure of btree_gin indexscans with "char" type and </<=
operators.
As a result of confusion about whether the "char" type is signed or
unsigned, scans for index searches like "col < 'x'" or "col <= 'x'"
would start at the middle of the index not the left end, thus missing
many or all of the entries they should find. Fortunately, this
is not a symptom of index corruption. It's only the search logic
that is broken, and we can fix it without unpleasant side-effects.
Per report from Jason Kim. This has been wrong since btree_gin's
beginning, so back-patch to all supported branches.
Discussion: https://postgr.es/m/20210810001649.htnltbh7c63re42p@jasonk.me
---
contrib/btree_gin/btree_gin.c | 2 +-
contrib/btree_gin/expected/char.out | 11 +++++++++--
2 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/contrib/btree_gin/btree_gin.c b/contrib/btree_gin/btree_gin.c
index e05b5c60ca5..c50d68ce186 100644
--- a/contrib/btree_gin/btree_gin.c
+++ b/contrib/btree_gin/btree_gin.c
@@ -357,7 +357,7 @@ GIN_SUPPORT(bpchar, true, leftmostvalue_text, bpcharcmp)
static Datum
leftmostvalue_char(void)
{
- return CharGetDatum(SCHAR_MIN);
+ return CharGetDatum(0);
}
GIN_SUPPORT(char, false, leftmostvalue_char, btcharcmp)
diff --git a/contrib/btree_gin/expected/char.out b/contrib/btree_gin/expected/char.out
index 09e0315de0a..6563546d3ce 100644
--- a/contrib/btree_gin/expected/char.out
+++ b/contrib/btree_gin/expected/char.out
@@ -7,12 +7,19 @@ CREATE INDEX idx_char ON test_char USING gin (i);
SELECT * FROM test_char WHERE i<'d'::"char" ORDER BY i;
i
---
-(0 rows)
+ a
+ b
+ c
+(3 rows)
SELECT * FROM test_char WHERE i<='d'::"char" ORDER BY i;
i
---
-(0 rows)
+ a
+ b
+ c
+ d
+(4 rows)
SELECT * FROM test_char WHERE i='d'::"char" ORDER BY i;
i