Fix leaks with functions in DML

.unreleased/fix_7088

@@ -0,0 +1,2 @@
+Fixes: #7088 Fix leaks with functions in DML
+Thanks: @Kazmirchuk for reporting this

src/cache.c

@@ -229,8 +229,16 @@ release_subtxn_pinned_caches(SubTransactionId subtxnid, bool abort)
 {
 	ListCell *lc;
 
-	/* Need a copy because cache_release will modify pinned_caches */
+	/*
+	 * Need a copy because cache_release will modify pinned_caches.
+	 *
+	 * This needs to be allocated in pinned cache memory context.
+	 * Otherwise leaks ensue if CurTransactionContext (which is the
+	 * CurrentMemoryContext) gets used!
+	 */
+	MemoryContext old = MemoryContextSwitchTo(pinned_caches_mctx);
 	List *pinned_caches_copy = list_copy(pinned_caches);
+	MemoryContextSwitchTo(old);
 
 	/* Only release caches created in subtxn */
 	foreach (lc, pinned_caches_copy)

test/expected/copy_memory_usage.out

@@ -59,3 +59,40 @@ select * from portal_memory_log where (
 ----+-------
 (0 rows)
 
+-- Test plpgsql leaks
+CREATE TABLE test_ht(tm timestamptz, val float8);
+SELECT * FROM create_hypertable('test_ht', 'tm');
+NOTICE:  adding not-null constraint to column "tm"
+ hypertable_id | schema_name | table_name | created 
+---------------+-------------+------------+---------
+             2 | public      | test_ht    | t
+(1 row)
+
+-- Use a plpgsql function to insert into the hypertable
+CREATE OR REPLACE FUNCTION to_double(_in text, INOUT _out double precision)
+LANGUAGE plpgsql IMMUTABLE parallel safe
+AS $$
+BEGIN
+    SELECT CAST(_in AS double precision) INTO _out;
+EXCEPTION WHEN others THEN
+    --do nothing: _out already carries default
+END;
+$$;
+-- TopTransactionContext usage needs to remain the same after every insert
+-- There was a leak earlier in the child CurTransactionContext
+BEGIN;
+INSERT INTO test_ht VALUES ('1980-01-01 00:00:00-00', to_double('23.11', 0));
+SELECT sum(total_bytes) from pg_backend_memory_contexts where parent = 'TopTransactionContext';
+  sum  
+-------
+ 16384
+(1 row)
+
+INSERT INTO test_ht VALUES ('1980-02-01 00:00:00-00', to_double('24.11', 0));
+SELECT sum(total_bytes) from pg_backend_memory_contexts where parent = 'TopTransactionContext';
+  sum  
+-------
+ 16384
+(1 row)
+
+COMMIT;

test/sql/copy_memory_usage.sql

@@ -56,3 +56,25 @@ select * from portal_memory_log where (
         from portal_memory_log
 );
 
+-- Test plpgsql leaks
+CREATE TABLE test_ht(tm timestamptz, val float8);
+SELECT * FROM create_hypertable('test_ht', 'tm');
+-- Use a plpgsql function to insert into the hypertable
+CREATE OR REPLACE FUNCTION to_double(_in text, INOUT _out double precision)
+LANGUAGE plpgsql IMMUTABLE parallel safe
+AS $$
+BEGIN
+    SELECT CAST(_in AS double precision) INTO _out;
+EXCEPTION WHEN others THEN
+    --do nothing: _out already carries default
+END;
+$$;
+
+-- TopTransactionContext usage needs to remain the same after every insert
+-- There was a leak earlier in the child CurTransactionContext
+BEGIN;
+INSERT INTO test_ht VALUES ('1980-01-01 00:00:00-00', to_double('23.11', 0));
+SELECT sum(total_bytes) from pg_backend_memory_contexts where parent = 'TopTransactionContext';
+INSERT INTO test_ht VALUES ('1980-02-01 00:00:00-00', to_double('24.11', 0));
+SELECT sum(total_bytes) from pg_backend_memory_contexts where parent = 'TopTransactionContext';
+COMMIT;