Add some comments about the safety of accessing rolpassword without using

the normal heap_getattr() machinery.  Per Greg Stark.

diff --git a/src/backend/utils/init/flatfiles.c b/src/backend/utils/init/flatfiles.c
index 2399408d3065b7557637c0cfe9f9371490ef0df8..774dfdc99d5de4d9647ed63adb28b8795f19fdcb 100644 (file)
--- a/src/backend/utils/init/flatfiles.c
+++ b/src/backend/utils/init/flatfiles.c
@@ -441,7 +441,10 @@ write_auth_file(Relation rel_authid, Relation rel_authmem)
                 * We can't use heap_getattr() here because during startup we will not
                 * have any tupdesc for pg_authid.      Fortunately it's not too hard to
                 * work around this.  rolpassword is the first possibly-null field so
-                * we can compute its offset directly.
+                * we can compute its offset directly.  Note that this only works
+                * reliably because the preceding field (rolconnlimit) is int4, and
+                * therefore rolpassword is always 4-byte-aligned, and will be at
+                * the same offset no matter whether it uses 1-byte or 4-byte header.
                 */
                tp = (char *) tup + tup->t_hoff;
                off = offsetof(FormData_pg_authid, rolpassword);
@@ -460,6 +463,10 @@ write_auth_file(Relation rel_authid, Relation rel_authmem)
                        /*
                         * The password probably shouldn't ever be out-of-line toasted; if
                         * it is, ignore it, since we can't handle that in startup mode.
+                        *
+                        * It is entirely likely that it's 1-byte format not 4-byte, and
+                        * theoretically possible that it's compressed inline, but textout
+                        * should be able to handle those cases even in startup mode.
                         */
                        if (VARATT_IS_EXTERNAL(DatumGetPointer(datum)))
                                auth_info[curr_role].rolpassword = pstrdup("");