Re: [CLOBBER_CACHE]Server crashed with segfault 11 while executing clusterdb

I wrote:
> Michael Paquier <michael@paquier.xyz> writes:
>> One bisect later, the winner is:
>> commit: 3d351d916b20534f973eda760cde17d96545d4c4
>> author: Tom Lane <tgl@sss.pgh.pa.us>
>> date: Sun, 30 Aug 2020 12:21:51 -0400
>> Redefine pg_class.reltuples to be -1 before the first VACUUM or ANALYZE.

> I think that's an artifact.  That commit didn't touch anything related to
> relation opening or closing.  What it could have done, though, is change
> CLUSTER's behavior on this empty table from use-an-index to use-a-seqscan,
> thus causing us to follow the buggy code path where before we didn't.

On closer inspection, I believe the true culprit is c6b92041d,
which did this:

      */
     if (RelationNeedsWAL(state->rs_new_rel))
-        heap_sync(state->rs_new_rel);
+        smgrimmedsync(state->rs_new_rel->rd_smgr, MAIN_FORKNUM);
 
     logical_end_heap_rewrite(state);

heap_sync was careful about opening rd_smgr, the new code not so much.

I read the rest of that commit and didn't see any other equivalent
bugs, but I might've missed something.

            regards, tom lane