On 11/03/16 22:29, Robert Haas wrote:
On Thu, Mar 10, 2016 at 8:54 PM, Petr Jelinek <p...@2ndquadrant.com> wrote:
I am not talking about extension locks, the lock queue can be long because
there is concurrent DDL for example and then once DDL finishes suddenly 100
connections that tried to insert into table will try to get extension lock
and this will add 2000 new pages when much fewer was actually needed. I
guess that's fine as it's corner case and it's only 16MB even in such
extreme case.

I don't really understand this part about concurrent DDL.  If there
were concurrent DDL going on, presumably other backends would be
blocked on the relation lock, not the relation extension lock - and it
doesn't seem likely that you'd often have a huge pile-up of inserters
waiting on concurrent DDL.  But I guess it could happen.

Yeah I was thinking about the latter part and as I said it's very rare case, but I did see something similar couple of times in the wild. It's not objection against committing this patch though, in fact I think it can be committed as is.

  Petr Jelinek                  http://www.2ndQuadrant.com/
  PostgreSQL Development, 24x7 Support, Training & Services

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