postgrespro.git / summary / log / commit / refs

commit    f37ff03478aefb5e01d748b85ad86e6213624992
Author:   Thomas Munro <tmunro@postgresql.org>
Date:     Sun Jan 26 20:05:27 2020 +0000

    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 85b7115400..c5b771c531 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];


[parent: 215824f9188a]