RE: Add tests for concurrent DML retry paths in logical replication apply

Dear Bharath,

> While reading the logical replication apply code in execReplication.c, I noticed
> that the retry paths in RelationFindReplTupleByIndex and RelationFindReplTupleSeq
> for concurrent updates and deletes have no test coverage [1]. Specifically,
> when the same tuple is being updated/deleted on the publisher and subscriber at
> the same time, the dirty snapshot finds the tuple being modified by another
> transaction, the apply worker waits and retries the index/sequential scan.

Good catch.

> The attached patch adds an injection point before table_tuple_lock and a TAP test
> exercising these retry paths, hitting both TM_Updated and TM_Deleted.

I read the code briefly. Here are questions:

1.
The test looks like to add the test for retry acquiring the lock. But there is
another retry path, which waits till xwait finishes. Do you have a reason to
skip testing?

2.
Is it OK to use the same injection point name twice? I cannot find the existing
case.

Best regards,
Hayato Kuroda
FUJITSU LIMITED