From f37ff03478aefb5e01d748b85ad86e6213624992 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Mon, 27 Jan 2020 09:05:27 +1300 Subject: [PATCH] Refactor confusing code in _mdfd_openseg(). As reported independently by a couple of people, _mdfd_openseg() is coded in a way that seems to imply that the segments could be opened in an order that isn't strictly sequential. Even if that were true, it's also using the wrong comparison. It's not an active bug, since the condition is always true anyway, but it's confusing, so replace it with an assertion. Author: Thomas Munro Reviewed-by: Andres Freund, Kyotaro Horiguchi, Noah Misch Discussion: https://postgr.es/m/CA%2BhUKG%2BNBw%2BuSzxF1os-SO6gUuw%3DcqO5DAybk6KnHKzgGvxhxA%40mail.gmail.com Discussion: https://postgr.es/m/20191222091930.GA1280238%40rfd.leadboat.com --- src/backend/storage/smgr/md.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c index 85b71154006..c5b771c5311 100644 --- a/src/backend/storage/smgr/md.c +++ b/src/backend/storage/smgr/md.c @@ -1100,8 +1100,13 @@ _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];