Re: cache lookup failed for relation X

"Wei Wu" <w(dot)wu(at)delcan(dot)com> writes:
> Basically, we have a table X, trying to drop
> it would result an error message below:
> cache lookup failed for relation XXXXX

You've got missing catalog rows, apparently.

> I am using PgAdmin and I can still view the schema of this table, but
> any operation on it would get the above error.

Hmmm ... how long since the system catalogs in this database were
vacuumed?

> I am also wondering whether this problem has been fixed in newer
> PostgreSQL releases.
> BTW, our postgreSQL version is 7.4.3.

It's hard to say, but you are three and a half years behind on bug fixes,
some of which certainly could have led to corruption of this sort.
You really should be running 7.4.19. Read the release notes here:
http://www.postgresql.org/docs/7.4/static/release.html

regards, tom lane