"Kangmo, Kim" <ilvsusie@hanafos.com> writes:
> If the index on the same class,
> two concurrent CREATE INDEX command can update pg_class.relpages
> at the same time.
Or try to, anyway. The problem here is that the code that updates
system catalogs is not prepared to cope with concurrent updates
to the same tuple.
> I guess that is not a bug of pgsql, but a weak point of
> MVCC DBMS.
No, it's not a limitation of MVCC per se, it's only an implementation
shortcut for catalog updates. Fixing this across all system catalog
updates seems more trouble than it's worth. It'd be nice if the
concurrent-CREATE-INDEX case worked, though.
regards, tom lane