Re: Min Xid problem proposal

Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> My proposal to solve that problem, is to make any transaction that
> inserts or modifies tuples in a table that is marked as frozen, unfreeze
> it first. The problem I had last time was finding a good spot in the
> code for doing so. I'm now proposing to do it in the parser, in
> setTargetTable().

My god, no. Do you have any idea how many paths for updates you've missed?
(Think about prepared plans for starters.)

Furthermore, you can't do this in the way you propose (non-WAL-logged
update to pg_class). What if the system crashes without ever having
written this update to disk? The inserted tuples might have made it ---
whether they're committed or not doesn't matter, you've still blown it.

I don't see any very good argument for allowing this mechanism to set
minxid = FrozenXid in the first place. If there are only frozenXid in
the table, set minxid = current XID. That eliminates the entire problem
at a stroke.

(Yes, I know what you are going to say. The idea of freezing a table
and then never having to vacuum it at all is NOT worth the cost of
putting in a mechanism that would guarantee its safety.)

regards, tom lane