Michael Paesold wrote:
Alvaro Herrera wrote:
So what you are proposing above amounts to setting scale factor = 0.05.
The threshold is unimportant -- in the case of a big table it matters
not if it's 0 or 1000, it will be almost irrelevant in calculations.  In
the case of small tables, then the table will be vacuumed in almost
every iteration if the threshold is 0, which is fine because the table
is small anyway.  So why not let the threshold be 0 and be done with it?

For very small tables, setting a threshold of 0 could mean a vacuum after every single row update (or every other row). I think that is just burning cycles. What about a threshold of 10 or 50, to have at least some sanity limit? Even though the cost of vacuum of a small table is low, it is still not free, IMHO, no?

A bit off-topic (because probably not realistic in a 8.3 timeframe) -
but maybe the threshold should be specified in terms of "expected number of
pages to be freed", instead specifing a bias for the number of modified
rows as it is done now. Then "1" would probably be a reasonable default, because
a vacuum that won't free at least one page seems to be not really worth
the effort - it won't safe any future IO bandwith.

Just an idea I got while following this thread...

greetings, Florian Pflug

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