Re: [HACKERS] Arrays broken on temp tables

> Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> writes:
> >> The bottom line here is that we mustn't generate separate RTEs for the
> >> logical and physical table names.
>
> > Are you saying a join on a temp table will not work?
>
> Not at all; I'm saying that it's incorrect to generate a join for a
> simple UPDATE. What we had was
>
> UPDATE table SET arrayfield[sub] = val;
>
> which is really implemented as (more or less)
>
> UPDATE table SET arrayfield = ARRAYINSERT(arrayfield, sub, val);
>
> which works fine as long as you apply the computation and update once
> per tuple in the table (or once per tuple selected by WHERE, if there
> is one). But for a temp table, what really gets emitted from the
> parser is effectively like
>
> UPDATE logtable SET arrayfield = arrayinsert(phytable.field,
> sub, val)
> FROM logtable phytable;
>
> This is a Cartesian join, meaning that each tuple in
> logtable-as-destination will be processed in combination with each tuple
> in logtable-as-phytable. The particular case Kristofer reported
> implements the join as a nested loop with logtable-as-destination as the
> inner side of the join. So, each target tuple gets updated once with
> an arrayfield value computed off each available source tuple --- and
> when the dust settles, they've all got the value computed from the last
> source tuple. That's why they're all the same in his bug report.
>
> Adding a WHERE clause limits the damage, but the target tuples will all
> still get the same value, if I'm visualizing the behavior correctly.
> It's the wrong thing in any case; the very best you could hope for is
> that the tuples all manage to get the right values after far more
> processing than necessary. There should be no join for a simple UPDATE.

OK, I see it now. They are assigning the relname at this point using
the in-tuple relname, which is the physical name, not the logical name.

If I look at all calls to RelationGetRelationName(), I can see several
problem cases where the code it assigning the rel/refname based on the
in-tuple name.

Ideas? Should i add reverse-lookup code in temprel.c, and make the
lookups happen for those cases?

--
Bruce Momjian | http://www.op.net/~candle
maillist(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026