Re: playing with catalog tables limits? dangers? was: seq bug 2073 and time machine

Ivan Sergio Borgonovo <mail(at)webthatworks(dot)it> writes:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> wrote:
>> If you're feeling corageous, you can remove the pg_depend entries
>> for that sequence. Make sure to try it in a transaction and drop

> I'd like to understand better the risks of being courageous?
> I think my life would be easier if I'd know when it is safe to put
> hands in the system tables.

Well, it's safe if (a) you know what you're doing, (b) you don't
make any mistakes, and (c) you don't forget any changes needed to
keep all the catalogs consistent.

You can protect yourself against (b) by using a transaction, but
the other two tend to require hacker-grade knowledge of how the
backend works, so we try to discourage people from doing it.
pg_depend in particular tends to have rather obscure contents,
and what's worse is that messing it up usually doesn't have any
immediately-obvious consequences.

regards, tom lane