Re: ALTER tbl rewrite loses CLUSTER ON index

On 2020-Apr-02, Michael Paquier wrote:

> Now, regarding patch 0002, note that you have a problem for this part:
> - tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(indexOid));
> - if (!HeapTupleIsValid(tuple)) /* probably can't happen */
> - {
> - relation_close(OldHeap, AccessExclusiveLock);
> - pgstat_progress_end_command();
> - return;
> - }
> - indexForm = (Form_pg_index) GETSTRUCT(tuple);
> - if (!indexForm->indisclustered)
> + if (!get_index_isclustered(indexOid))
> {
> - ReleaseSysCache(tuple);
> relation_close(OldHeap, AccessExclusiveLock);
> pgstat_progress_end_command();
> return;
> }
> - ReleaseSysCache(tuple);
>
> On an invalid tuple for pg_index, the new code would issue an error,
> while the old code would just return.

I don't think we need to worry about that problem, because we already
checked that the pg_class tuple for the index is there two lines above.
The pg_index tuple cannot have gone away on its own; and the index can't
be deleted either, because cluster_rel holds AEL on the table. There
isn't "probably" about the can't-happen condition, is there?

--
Álvaro Herrera https://www.2ndQuadrant.com/
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