Fix session lock leak in ALTER DATABASE SET TABLESPACE for utility mode

movedb() acquires a session-level AccessExclusiveLock on the database
via MoveDbSessionLockAcquire(). The release in CommitTransaction()
only checked for GP_ROLE_DISPATCH and IS_SINGLENODE(), missing
GP_ROLE_UTILITY. This caused the lock to leak in standalone backends
(e.g. TAP tests), triggering a proc.c assertion failure at exit:

  FailedAssertion("SHMQueueEmpty(&(MyProc->myProcLocks[i]))")

Add GP_ROLE_UTILITY to the release condition.

Also fix a spurious "could not read symbolic link" log message when
dropping in-place tablespaces: readlink() on a directory returns
EINVAL, which is expected and can be safely skipped.

Fixes #1626

Author: yjhjstz

src/backend/access/transam/xact.c

@@ -3036,13 +3036,15 @@ CommitTransaction(void)
 	DoPendingDbDeletes(true);
 
 	/*
-	 * Only QD holds the session level lock this long for a movedb operation.
-	 * This is to prevent another transaction from moving database objects into
-	 * the source database oid directory while it is being deleted. We don't
-	 * worry about aborts as we release session level locks automatically during
-	 * an abort as opposed to a commit.
-	 */
-	if(Gp_role == GP_ROLE_DISPATCH || IS_SINGLENODE())
+	 * Release the session level lock held for a movedb operation. This is to
+	 * prevent another transaction from moving database objects into the source
+	 * database oid directory while it is being deleted. We don't worry about
+	 * aborts as we release session level locks automatically during an abort
+	 * as opposed to a commit. We must also release in utility mode (e.g.
+	 * standalone backends used in TAP tests).
+	 */
+	if (Gp_role == GP_ROLE_DISPATCH || Gp_role == GP_ROLE_UTILITY ||
+		IS_SINGLENODE())
 		MoveDbSessionLockRelease();
 
 	/*

src/backend/commands/tablespace.c

@@ -1230,14 +1230,19 @@ destroy_tablespace_directories(Oid tablespaceoid, bool redo)
 	linkloc = pstrdup(linkloc_with_version_dir);
 	get_parent_directory(linkloc);
 
-	/* Remove the symlink target directory if it exists or is valid. */
+	/*
+	 * Remove the symlink target directory if it exists or is valid.
+	 * If linkloc is a directory (e.g. in-place tablespace), readlink()
+	 * will fail with EINVAL, which we can safely skip.
+	 */
 	rllen = readlink(linkloc, link_target_dir, sizeof(link_target_dir));
 	if(rllen < 0)
 	{
-		ereport(redo ? LOG : ERROR,
-				(errcode_for_file_access(),
-					errmsg("could not read symbolic link \"%s\": %m",
-						   linkloc)));
+		if (errno != EINVAL)
+			ereport(redo ? LOG : ERROR,
+					(errcode_for_file_access(),
+						errmsg("could not read symbolic link \"%s\": %m",
+							   linkloc)));
 	}
 	else if(rllen >= sizeof(link_target_dir))
 	{