Re: auto-vacuum & Negative "anl" Values

Tom Lane wrote:

Alvaro Herrera <alvherre@commandprompt.com> writes:

+ /* last_anl_tuples must never exceed n_live_tuples */

If we actually believe the above statement, it seems like your patch

to pgstat_recv_tabstat() opens a new issue: with that patch, it is

possible for pgstat_recv_tabstat() to decrease n_live_tuples, and

therefore a clamp needs to be applied in pgstat_recv_tabstat() too.

No?

Hmm, yeah.

The reason I didn't patch it myself is that I'm not quite clear on what

*should* be happening here.  What effect should a large delete have on

the ANALYZE threshold, exactly?  You could argue that a deletion

potentially changes the statistics (by omission), and therefore inserts,

updates, and deletes should equally count +1 towards the analyze

threshold.  I don't think we are implementing that though.  If we want

to do it that way, I suspect last_anl_tuples as currently defined is not

the right comparison point.

Maybe what we should do is revert the pgstat_recv_tabstat() part of the

patch in 8.1, and consider redefining last_anl_tuples in HEAD.  Caffeine

is not high enough yet to propose anything sensible, but I'll think

about it a bit later.

-- 

Alvaro Herrera                                http://www.CommandPrompt.com/

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