Strange coding in _mdfd_openseg() - Mailing list pgsql-hackers

Hello,

I think the following conditional code is misleading, and I wonder if
it would be better like so:

--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -1787,8 +1787,13 @@ _mdfd_openseg(SMgrRelation reln, ForkNumber
forknum, BlockNumber segno,
        if (fd < 0)
                return NULL;

-       if (segno <= reln->md_num_open_segs[forknum])
-               _fdvec_resize(reln, forknum, segno + 1);
+       /*
+        * Segments are always opened in order from lowest to highest,
so we must
+        * be adding a new one at the end.
+        */
+       Assert(segno == reln->md_num_open_segs[forknum]);
+
+       _fdvec_resize(reln, forknum, segno + 1);

        /* fill the entry */
        v = &reln->md_seg_fds[forknum][segno];

I think the condition is always true, and with == it would also always
be true.  If that weren't the case, the call to _fdvec_resize() code
would effectively leak vfds.

-- 
Thomas Munro
https://enterprisedb.com