On 10/22/15 6:39 PM, Alvaro Herrera wrote:
Jim Nasby wrote:
That would be the minimal-impact version, yes. But I suspect if we went
through the trouble to do that, it would be just as easy to attempt the
freeze regardless of what scan_all is set to.
You mean if !scan_all we conditional-get the cleanup lock, if we get it
then prune, if not then freeze? That seems nice on paper but I think
it's useless because unless scan_all is true, then relfrozenxid doesn't
advance anyway.
Actually, advancing relfrozenxid only depends on having hit all pages in
the table, which can happen even if !scan_all. Aside from that, once the
freeze map hits this would be useful in setting bits there.
What I wish I knew is whether this problem was worth worrying about or not.
Hopefully the extra logging in 9.5 will shed some light at some point...
As I recall, Andres says it isn't, but I have recollections of scans
that take a very long time to finish because they keep running into a
vacuum that has a page locked.
I guess lets see if the new logging we have on this sheds some light then.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
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