On Wed, Jun 1, 2011 at 7:28 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, May 26, 2011 at 12:34 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Alvaro Herrera <alvherre@commandprompt.com> writes:
>>> Excerpts from Euler Taveira de Oliveira's message of jue may 26 12:00:0=
5 -0400 2011:
>>>> I think we should emit the real cause in those cases, if possible (not=
too
>>>> much overhead). The message would be "Unlogged table content is not av=
ailable
>>>> in standby server".
>>
>>> I guess what it should do is create an empty file in the slave.
>>
>> Probably it should, because won't the table malfunction after the slave
>> is promoted to master, if there's no file at all there? =A0Or will the
>> process of coming live create an empty file even if there was none?
>
> Coming live creates an empty file.
>
>> But Euler is pointing out a different issue, which is usability. =A0If t=
he
>> slave just acts like the table is present but empty, we are likely to
>> get bug reports about that too. =A0An error telling you you aren't allow=
ed
>> to access such a table on slaves would be more user-friendly, if we can
>> do it without too much pain.
>
> I looked into this a bit. =A0A few observations:
>
> (1) This problem is actually not confined to unlogged tables;
> temporary tables have the same issue. =A0For example, if you create a
> temporary table on the master and then, on the slave, do SELECT * FROM
> =A0pg_temp_3.hi_mom (or whatever the name of the temp schema where the
> temp table is) you get the same error. =A0In fact I suspect if you took
> a base backup that included the temporary relation and matched the
> backend ID you could even manage to read out the old contents (modulo
> any fun and exciting XID wraparound issues). =A0But the problem is of
> course more noticeable for unlogged tables since they're not hidden
> away in a special funny schema.
Seems like you're trying to fix the problem directly, which as you
say, has problems.
At some point we resolve from a word mentioned in the FROM clause to a
relfilenode.
Surely somewhere there we can notice its unlogged before we end up
down in the guts of smgr?
--=20
=A0Simon Riggs=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 http:/=
/www.2ndQuadrant.com/
=A0PostgreSQL Development, 24x7 Support, Training & Services
