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Refactor confusing code in _mdfd_openseg().

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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
This commit is contained in:
Thomas Munro 2020-01-27 09:05:27 +13:00
parent 215824f918
commit f37ff03478
1 changed files with 7 additions and 2 deletions
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9
src/backend/storage/smgr/md.c
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@ -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];