Re: Upper limit arguments of pg_logical_slot_xxx_changes functions accept invalid values

On Wed, Jul 11, 2018 at 8:58 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> While reading the replication slot codes, I found a wrong assignment
> in pg_logical_slot_get_changes_guts() function as follows.
>
> if (PG_ARGISNULL(2))
> upto_nchanges = InvalidXLogRecPtr;
> else
> upto_nchanges = PG_GETARG_INT32(2);
>
> Since the upto_nchanges is an integer value we should set 0 meaning
> unlimited instead of InvalidXLogRecPtr. Since InvalidXLogRecPtr is
> actually 0 this function works fine so far.

If somebody changes InvalidXLogRecPtr to (uint64)-1, then it breaks as
the code is written. On the other hand, if somebody reverted
0ab9d1c4b31622e9176472b4276f3e9831e3d6ba, it would keep working as
written but break under your proposal.

I am not prepared to spend much time arguing about it, but I think we
should just leave this the way it is.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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