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commit    33b06a20016d8dd8dbdc1f6d6a9d79477c1104c5
Author:   David Rowley <drowley@postgresql.org>
Date:     Mon Jun 16 22:49:36 2025 +0000
First released in: 18.0

    Fix possible Assert failure in verify_compact_attribute()
    
    Sometimes the TupleDesc used in verify_compact_attribute() is shared
    among backends, and since CompactAttribute.attcacheoff gets updated
    during tuple deformation, it was possible that another backend would
    set attcacheoff on a given CompactAttribute in the small window of time
    from when the attcacheoff from the live CompactAttribute was being set
    in the 'tmp' CompactAttribute and before the Assert verifying that the
    live and tmp CompactAttributes matched.
    
    Here we adjust the code to make a copy of the live CompactAttribute so
    that we're not trying to Assert against a shared copy of it.
    
    Author: David Rowley <dgrowleyml@gmail.com>
    Reported-by: Alexander Lakhin <exclusion@gmail.com>
    Discussion: https://postgr.es/m/7195e408-758c-4031-8e61-4f842c716ac0@gmail.com


 src/backend/access/common/tupdesc.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/backend/access/common/tupdesc.c b/src/backend/access/common/tupdesc.c
index ffd0c78f905..020d00cd01c 100644
--- a/src/backend/access/common/tupdesc.c
+++ b/src/backend/access/common/tupdesc.c
@@ -142,10 +142,17 @@ void
 verify_compact_attribute(TupleDesc tupdesc, int attnum)
 {
 #ifdef USE_ASSERT_CHECKING
-	CompactAttribute *cattr = &tupdesc->compact_attrs[attnum];
+	CompactAttribute cattr;
 	Form_pg_attribute attr = TupleDescAttr(tupdesc, attnum);
 	CompactAttribute tmp;
 
+	/*
+	 * Make a temp copy of the TupleDesc's CompactAttribute.  This may be a
+	 * shared TupleDesc and the attcacheoff might get changed by another
+	 * backend.
+	 */
+	memcpy(&cattr, &tupdesc->compact_attrs[attnum], sizeof(CompactAttribute));
+
 	/*
 	 * Populate the temporary CompactAttribute from the corresponding
 	 * Form_pg_attribute
@@ -156,11 +163,11 @@ verify_compact_attribute(TupleDesc tupdesc, int attnum)
 	 * Make the attcacheoff match since it's been reset to -1 by
 	 * populate_compact_attribute_internal.  Same with attnullability.
 	 */
-	tmp.attcacheoff = cattr->attcacheoff;
-	tmp.attnullability = cattr->attnullability;
+	tmp.attcacheoff = cattr.attcacheoff;
+	tmp.attnullability = cattr.attnullability;
 
 	/* Check the freshly populated CompactAttribute matches the TupleDesc's */
-	Assert(memcmp(&tmp, cattr, sizeof(CompactAttribute)) == 0);
+	Assert(memcmp(&tmp, &cattr, sizeof(CompactAttribute)) == 0);
 #endif
 }
 


[parent: e9a3615a5224]