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commit    3e2e0d5ad7fcb89d18a71cbfc885ef184e1b6f2e
Author:   Peter Eisentraut <peter@eisentraut.org>
Date:     Fri Dec 22 20:44:55 2023 +0000
First released in: 17.0

    Set all variable-length fields of pg_attribute to null on column drop
    
    When a column is dropped, the fields attacl, attoptions, and
    attfdwoptions were kept unchanged.  This is probably harmless, but it
    seems wasteful, and leaves potentially dangling data lying around (for
    example, attacl could contain references to users that are later also
    dropped).
    
    Change this to set those fields to null when a column is marked as
    dropped.
    
    Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
    Discussion: https://www.postgresql.org/message-id/flat/249d819d-1763-4580-8110-0bf91a0f08b7@eisentraut.org


 src/backend/catalog/heap.c | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index 7224d966950..b93894889d6 100644
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -1647,6 +1647,9 @@ RemoveAttributeById(Oid relid, AttrNumber attnum)
 	HeapTuple	tuple;
 	Form_pg_attribute attStruct;
 	char		newattname[NAMEDATALEN];
+	Datum		valuesAtt[Natts_pg_attribute] = {0};
+	bool		nullsAtt[Natts_pg_attribute] = {0};
+	bool		replacesAtt[Natts_pg_attribute] = {0};
 
 	/*
 	 * Grab an exclusive lock on the target table, which we will NOT release
@@ -1695,24 +1698,24 @@ RemoveAttributeById(Oid relid, AttrNumber attnum)
 			 "........pg.dropped.%d........", attnum);
 	namestrcpy(&(attStruct->attname), newattname);
 
-	/* clear the missing value if any */
-	if (attStruct->atthasmissing)
-	{
-		Datum		valuesAtt[Natts_pg_attribute] = {0};
-		bool		nullsAtt[Natts_pg_attribute] = {0};
-		bool		replacesAtt[Natts_pg_attribute] = {0};
-
-		/* update the tuple - set atthasmissing and attmissingval */
-		valuesAtt[Anum_pg_attribute_atthasmissing - 1] =
-			BoolGetDatum(false);
-		replacesAtt[Anum_pg_attribute_atthasmissing - 1] = true;
-		valuesAtt[Anum_pg_attribute_attmissingval - 1] = (Datum) 0;
-		nullsAtt[Anum_pg_attribute_attmissingval - 1] = true;
-		replacesAtt[Anum_pg_attribute_attmissingval - 1] = true;
-
-		tuple = heap_modify_tuple(tuple, RelationGetDescr(attr_rel),
-								  valuesAtt, nullsAtt, replacesAtt);
-	}
+	/* Clear the missing value */
+	attStruct->atthasmissing = false;
+	nullsAtt[Anum_pg_attribute_attmissingval - 1] = true;
+	replacesAtt[Anum_pg_attribute_attmissingval - 1] = true;
+
+	/*
+	 * Clear the other variable-length fields.  This saves some space in
+	 * pg_attribute and removes no longer useful information.
+	 */
+	nullsAtt[Anum_pg_attribute_attacl - 1] = true;
+	replacesAtt[Anum_pg_attribute_attacl - 1] = true;
+	nullsAtt[Anum_pg_attribute_attoptions - 1] = true;
+	replacesAtt[Anum_pg_attribute_attoptions - 1] = true;
+	nullsAtt[Anum_pg_attribute_attfdwoptions - 1] = true;
+	replacesAtt[Anum_pg_attribute_attfdwoptions - 1] = true;
+
+	tuple = heap_modify_tuple(tuple, RelationGetDescr(attr_rel),
+							  valuesAtt, nullsAtt, replacesAtt);
 
 	CatalogTupleUpdate(attr_rel, &tuple->t_self, tuple);
 


[parent: e2b73f4a4de6]