Re: pgsql: Change timeline field of IDENTIFY_SYSTEM to int8

On 04.07.22 07:55, Tom Lane wrote:
> Peter Eisentraut <peter(at)eisentraut(dot)org> writes:
>> Change timeline field of IDENTIFY_SYSTEM to int8
>
> Surely this patch is far from complete?
>
> To start with, just a few lines down in IdentifySystem() the column
> is filled using Int32GetDatum not Int64GetDatum. I will get some
> popcorn and await the opinions of the 32-bit buildfarm animals.
>
> But what about whatever code is reading the output? And what if
> that code isn't v16? I can't believe that we can make a wire
> protocol change as summarily as this.

I think a client will either just read the string value and convert it
to some numeric type without checking what type was actually sent, or if
the client API is type-aware and automatically converts to a native type
of some sort, then it will probably already support 64-bit ints. Do you
see some problem scenario?

I'm seeing a bigger problem now, which is that our client code doesn't
parse bigger-than-int32 timeline IDs correctly.

libpqwalreceiver uses pg_strtoint32(), which will error on overflow.

pg_basebackup uses atoi(), so it will just truncate the value, except
for READ_REPLICATION_SLOT, where it uses atol(), so it will do the wrong
thing on Windows only.

There is clearly very little use for such near-overflow timeline IDs in
practice. But it still seems pretty inconsistent.