On Feb 1, 2007, at 10:57 AM, Tom Lane wrote:
ITAGAKI Takahiro <[EMAIL PROTECTED]> writes:
I'm thinking to add "the number of vacuumed tuples" to the message from vacuum. The stats collector will subtract the value from n_dead_tuples
instead of setting it to zero. This is also needed if we want to make
some kinds of "partial" vacuum methods.

This seems awfully dangerous to me, because then you are operating on
dead reckoning forever: there will be nothing that can correct an
inaccurate rowcount estimate, and in practice that means it will diverge
arbitrarily far from reality :-(, because of the inherent inaccuracies
of the stats system.  I think the risk of that is far worse than the
relatively small (or at least bounded) error arising from tuples not
seen by vacuum.

Yeah, it'd be better for vacuum to send a message stating how many dead rows it couldn't remove, ala:

DETAIL:  0 dead row versions cannot be removed yet.

Granted, not perfect, but better than what we have now.
Jim Nasby                                            [EMAIL PROTECTED]
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)

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