Re: WAL logging problem in 9.4.3?

On 2015-07-03 19:14:26 +0200, Martijn van Oosterhout wrote:
> Am I missing something. ISTM that if the truncate record was simply not
> logged at all everything would work fine. The whole point is that the
> table was created in this transaction and so if it exists the table on
> disk must be the correct representation.

That'd not work either. Consider:

BEGIN;
CREATE TABLE ...
INSERT;
TRUNCATE;
INSERT;
COMMIT;

If you replay that without a truncation wal record the second INSERT
will try to add stuff to already occupied space. And they can have
different lengths and stuff, so you cannot just ignore that fact.

> The broken index is just one symptom.

Agreed. I think the problem is something else though. Namely that we
reuse the relfilenode for heap_truncate_one_rel(). That's just entirely
broken afaics. We need to allocate a new relfilenode and write stuff
into that. Then we can forgo WAL logging the truncation record.

> If you insert a row before commit then after replay the tuple should be there still.

The insert would be WAL logged. COPY skips wal logging tho.