BUG #18286: "ERROR: could not open relation with OID 16391" error was encountered when reindexing

The following bug has been logged on the website:

Bug reference: 18286
Logged by: Fei Changhong
Email address: feichanghong(at)qq(dot)com
PostgreSQL version: 16.1
Operating system: Operating system: centos 7,Kernel version: 5.10.13
Description:

When reindex the partitioned table's index and the drop index are executed
concurrently, we may encounter the error "could not open relation with
OID".

The reconstruction of the partitioned table's index is completed in multiple
transactions and can be simply summarized into the following steps:
1. Obtain the oids of all partition indexes in the ReindexPartitions
function, and then commit the transaction to release all locks.
2. Reindex each index in turn
2.1 Start a new transaction
2.2 Check whether the index still exists
2.3 Call the reindex_index function to complete the index rebuilding
work
2.4 Submit transaction
There is no lock between steps 2.2 and 2.3 to protect the heap table and
index from being dropped, so whether the heap table still exists is checked
in the reindex_index function, but the index is not checked.
One fix I can think of is: after successfully opening the heap table in
reindex_index, check again whether the index still exists, Something like
this:

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 143fae01eb..21777ec98c 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -3594,6 +3594,17 @@ reindex_index(Oid indexId, bool
skip_constraint_checks, char persistence,
if (!heapRelation)
return;

+ /*
+ * Before opening the index, check if the index relation still exists.
+ * If index relation is gone, leave.
+ */
+ if (params->options & REINDEXOPT_MISSING_OK != 0 &&
+ !SearchSysCacheExists1(RELOID, ObjectIdGetDatum(indexId)))
+ {
+ table_close(heapRelation, NoLock);
+ return;
+ }
+
/*
* Switch to the table owner's userid, so that any index functions
are run
* as that user. Also lock down security-restricted operations
and

The above analysis is based on the latest master branch.

I'm not sure if my idea is reasonable, I hope you can give me some
suggestions. Thanks.

Best Regards,
Fei Changhong