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Re: Fix incorrect assignment of InvalidXLogRecPtr to a non-LSN variable. - Mailing list pgsql-hackers

From Steven Niu
Subject Re: Fix incorrect assignment of InvalidXLogRecPtr to a non-LSN variable.
Date
Msg-id MN2PR15MB302157CF81E30E07D5E4FA25A7CCA@MN2PR15MB3021.namprd15.prod.outlook.com
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In response to Fix incorrect assignment of InvalidXLogRecPtr to a non-LSN variable.  (Fujii Masao <masao.fujii@gmail.com>)
List pgsql-hackers
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Agreed. 

The definitions of upto_lsn and upyo_nchanges are different, so they should not be assigned the same form of value. 

      XLogRecPtr  upto_lsn;
      int32       upto_nchanges;
......
      if (PG_ARGISNULL(1))
            upto_lsn = InvalidXLogRecPtr;
      else
            upto_lsn = PG_GETARG_LSN(1);

      if (PG_ARGISNULL(2))
            upto_nchanges = InvalidXLogRecPtr;
      else
            upto_nchanges = PG_GETARG_INT32(2);

Thanks,
Steven

From: Fujii Masao <masao.fujii@gmail.com>
Sent: Wednesday, November 12, 2025 16:23
To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Fix incorrect assignment of InvalidXLogRecPtr to a non-LSN variable.

Hi,

I noticed that pg_logical_slot_get_changes_guts() assigns InvalidXLogRecPtr
to the local variable upto_nchanges, even though it's not LSN variable
(i.e., its type is int32, not XLogRecPtr). While this causes no functional issue
since InvalidXLogRecPtr is defined as 0, it's semantically incorrect.

I propose fixing this by setting upto_nchanges to 0 instead of
InvalidXLogRecPtr.
Attached is a patch implementing this change.

Regards,

--
Fujii Masao

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