[Catalog-sig] Untested patch for PyPI exceptions

["Martin v. Löwis"]

A.M. Kuchling schrieb:
> The completely untested patch below should remedy the occasional
> exceptions that PyPI is occasionally raising.  Can someone provide a
> sanity check for this patch?  (I'm not going to deploy it -- not
> familiar enough with the setup on the live site.)

I don't understand why this is necessary (although I trust that these
exceptions really occur).

Can any expert on Postgres please shed a light on it? The code currently
reads

        self.cursor.execute("lock table browse_tally")
        if self.is_cache_current():
            # overlapping update, just release the lock
            self.store.commit()
            return
        self.cursor.execute("delete from browse_tally")
        ...
        self.cursor.execute("update timestamps set value=now() where
name='browse_tally'")
        self.store.commit()

Now, this code gets an exception

psycopg.ProgrammingError: ERROR:  could not serialize access due to
concurrent update

delete from browse_tally

How is that possible? This code is the only code code updating
browse_tally (although multiple simultaneous processes may run the
same code); I would expect that the "lock table" statement prevents
concurrent updates.

Any help appreciated.

Regards,
Martin