Re: Feature freeze date for 8.1

The world rejoiced as matthew(at)zeut(dot)net ("Matthew T. O'Connor") wrote:
> Marc G. Fournier wrote:
>
>> On Fri, 29 Apr 2005, Christopher Browne wrote:
>>
>>> Some reasonable approximations might include:
>>> - How much disk I/O was recorded in the last 60 seconds?
>>> - How many application transactions (e.g. - invoices or such) were
>>> issued in the last 60 seconds (monitoring a sequence could be
>>> good enough).
>>
>>
>> Some way of doing a 'partial vacuum' would be nice ... where a
>> VACUUM could stop after it processed those '10 elderly tuples' and
>> on the next pass, resume from that point instead of starting from
>> the beginning again ...
>
> That is sorta what the vacuum delay settings accomplish.

What they do is orthogonal to that.

"Vacuum delay" prevents vacuum I/O from taking over the I/O bus.

Unfortunately, if you have a table with a very large number of _live_
tuples, there is no way to skip over those and only concentrate on the
dead ones.

In that scenario "vacuum delay" leads to the vacuum on the table
running for a Very, Very Long Time, because it sits there delaying a
lot as it walks thru pages it never modifies. The one good news is
that, for any pages where no tuples are touched, the indices are also
left untouched.
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