Re: prevent immature WAL streaming

Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> On 2021-Nov-25, Tom Lane wrote:
>> Really?  AFAICS the WAL record contains the correct value, or at least
>> we should define that one as being correct, for precisely this reason.

> I don't know what is the correct value for a record that comes exactly
> after the page header.  But here's a patch that fixes the problem; and
> if a standby replays WAL written by an unpatched primary, it will be
> able to read past instead of dying of FATAL.

Meh ... but given the simplicity of the write-side fix, maybe changing
it is appropriate.

However, this seems too forgiving:

+    if (xlrec->overwritten_lsn != state->overwrittenRecPtr &&
+        xlrec->overwritten_lsn - SizeOfXLogShortPHD != state->overwrittenRecPtr &&
+        xlrec->overwritten_lsn - SizeOfXLogLongPHD != state->overwrittenRecPtr)

The latter two cases should only be accepted if overwrittenRecPtr is
exactly at a page boundary.

            regards, tom lane