Fix comments on wal_level=minimal, CREATE TABLESPACE and CREATE DATABASE.

Commit 97ddda8 removed the rmtree()
behavior from XLOG_TBLSPC_CREATE, obsoleting that part of the comment.
The comment's point about XLOG_DBASE_CREATE was wrong when commit
fa0f466 introduced the point.  (It
would have been accurate if that commit had predated commit
fbcbc5d introducing the second
checkpoint of CREATE DATABASE.)  Nothing can skip log_smgrcreate() on
the basis of wal_level=minimal, so don't comment on that.

Commit c6b9204 expanded WAL skipping
from five specific operations to relfilenodes generally, hence the
CreateDatabaseUsingFileCopy() comment change.

Discussion: https://postgr.es/m/20231008022204.cc@rfd.leadboat.com

Author: nmisch

src/backend/access/heap/heapam_handler.c

@@ -605,9 +605,7 @@ heapam_relation_set_new_filelocator(Relation rel,
 
 	/*
 	 * If required, set up an init fork for an unlogged table so that it can
-	 * be correctly reinitialized on restart.  Recovery may remove it while
-	 * replaying, for example, an XLOG_DBASE_CREATE* or XLOG_TBLSPC_CREATE
-	 * record.  Therefore, logging is necessary even if wal_level=minimal.
+	 * be correctly reinitialized on restart.
 	 */
 	if (persistence == RELPERSISTENCE_UNLOGGED)
 	{

src/backend/commands/dbcommands.c

@@ -644,9 +644,10 @@ CreateDatabaseUsingFileCopy(Oid src_dboid, Oid dst_dboid, Oid src_tsid,
 	 * make the XLOG entry for the benefit of PITR operations). This avoids
 	 * two nasty scenarios:
 	 *
-	 * #1: When PITR is off, we don't XLOG the contents of newly created
-	 * indexes; therefore the drop-and-recreate-whole-directory behavior of
-	 * DBASE_CREATE replay would lose such indexes.
+	 * #1: At wal_level=minimal, we don't XLOG the contents of newly created
+	 * relfilenodes; therefore the drop-and-recreate-whole-directory behavior
+	 * of DBASE_CREATE replay would lose such files created in the new
+	 * database between our commit and the next checkpoint.
 	 *
 	 * #2: Since we have to recopy the source database during DBASE_CREATE
 	 * replay, we run the risk of copying changes in it that were committed