Re: [HACKERS] md.c is feeling much better now, thank you

Tatsuo Ishii <t-ishii@sra.co.jp> writes:
> Ok. I will give another example that seems more serious.
> test=> aaa;
> ERROR:  parser: parse error at or near "aaa"
> -- transaction is aborted and the table file t1 is unlinked.
> test=> select * from t1;
> -- but parser doesn't know t1 does not exist any more.
> -- it tries to open t1 using mdopen(). (see including backtrace)
> -- mdopen() tries to open t1 and fails. In this case mdopen()
> -- creates t1!
> NOTICE:  (transaction aborted): queries ignored until END
> *ABORT STATE*

Hmm.  It seems a more straightforward solution would be to alter
pg_parse_and_plan so that the parser isn't even called if we have
already failed the current transaction; that is, the "queries ignored"
test should occur sooner.  I'm rather surprised to realize that
we do run the parser in this situation...

> I think the long range solution would be let parser obtain certain
> locks as Tom said.

That would not solve this particular problem, since the lock manager
wouldn't know any better than the parser that the table doesn't really
exist any more.

> Until that I propose following solution. It looks
> simple, safe and would be neccessary anyway (I don't know why that
> check had not been implemented). See included patches.

This looks like it might be a good change, but I'm not quite as sure
as you are that it won't have any bad effects.  Have you tested it?
        regards, tom lane