On Thu, Jan 28, 2016 at 8:41 AM, Amit Langote <amitlangot...@gmail.com> wrote:
> Or keep scanned_heap_pages as is and add a skipped_pages (or
> skipped_heap_pages). I guess the latter would be updated not only for
> all visible skipped pages but also pin skipped pages. That is,
> updating its counter right after vacrelstats->pinskipped_pages++ which
> there are a couple of instances of. Likewise a good (and only?) time
> to update the former's counter would be right after
> vacrelstats->scanned_pages++. Although, I see at least one place where
> both are incremented so maybe I'm not entirely correct about the last
> two sentences.

So I've spent a fair amount of time debugging really-long-running
VACUUM processes with customers, and generally what I really want to
know is:

>>> What block number are we at? <<<

Because, if I know that, and I can see how fast that's increasing,
then I can estimate whether the VACUUM is going to end in a reasonable
period of time or not.  So my preference is to not bother breaking out
skipped pages, but just report the block number and call it good.  I
will defer to a strong consensus on something else, but reporting the
block number has the advantage of being dead simple and, in my
experience, that would answer the question that I typically have.

Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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