Re: PATCH: logical_work_mem and logical streaming of large in-progress transactions

Tom Lane has raised a complaint on pgsql-commiters [1] about one of
the commits related to this work [2]. The new member wrasse is showing
Warning:

"/export/home/nm/farm/studio64v12_6/HEAD/pgsql.build/../pgsql/src/backend/replication/logical/reorderbuffer.c",
line 2510: Warning: Likely null pointer dereference (*(curtxn+272)):
ReorderBufferProcessTXN

The Warning is for line:
curtxn->concurrent_abort = true;

Now, we can simply fix this warning by adding an if check like:
if (curtxn)
curtxn->concurrent_abort = true;

However, on further discussion, it seems that is not sufficient here
because the callbacks can throw the surrounding error code
(ERRCODE_TRANSACTION_ROLLBACK) where we set concurrent_abort flag for
a completely different scenario. I think here we need a
stronger check to ensure that we set concurrent abort flag and do
other things in that check only when we are decoding non-committed
xacts. The idea I have is to additionally check that we are decoding
streaming or prepared transaction (the same check as we have for
setting curtxn) or we can check if CheckXidAlive is a valid
transaction id. What do you think?

[1] - https://www.postgresql.org/message-id/2752962.1619568098%40sss.pgh.pa.us
[2] - https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=7259736a6e5b7c7588fff9578370736a6648acbb

--
With Regards,
Amit Kapila.