Re: "ERROR: could not open relation with OID 16391" error was encountered when reindexing

> This is extremely nonspecific, as line numbers in our code change
> constantly. Please quote a chunk of code surrounding that
> and indicate which line you are trying to stop at.

Thanks for the suggestion, I've refined the steps below to reproduce:
1. Initialize the data
```
DROP TABLE IF EXISTS tbl_part;
CREATE TABLE tbl_part (a integer) PARTITION BY RANGE (a);
CREATE TABLE tbl_part_p1 PARTITION OF tbl_part FOR VALUES FROM (0) TO (10);
CREATE INDEX ON tbl_part(a);
```
2. session1 reindex and the gdb break after the reindex_index function successfully obtains the heapId, as noted in the code chunk below:

reindex_index(Oid indexId, bool skip_constraint_checks, char persistence,
const ReindexParams *params)
{
......
/*
* Open and lock the parent heap relation. ShareLock is sufficient since
* we only need to be sure no schema or data changes are going on.
*/
heapId = IndexGetRelation(indexId,
(params->options & REINDEXOPT_MISSING_OK) != 0);
====> gdb break at here
/* if relation is missing, leave */
if (!OidIsValid(heapId))
return;
```
REINDEX INDEX tbl_part_a_idx;
```
3. session2 drop index succeed

```
DROP INDEX tbl_part_a_idx;
```
4. session1 gdb continue

Best Regards,
Fei Changhong
Alibaba Cloud Computing Ltd.