Re: Scalability in postgres

От: david@lang.hm
Тема: Re: Scalability in postgres
Дата: ,
Msg-id: alpine.DEB.1.10.0906041747570.7953@asgard
(см: обсуждение, исходный текст)
Ответ на: Re: Scalability in postgres  (Robert Haas)
Ответы: Re: Scalability in postgres  (Robert Haas)
Список: pgsql-performance

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Scalability in postgres  (Fabrix, )
 Re: Scalability in postgres  (David Rees, )
  Re: Scalability in postgres  (Fabrix, )
   Re: Scalability in postgres  (Scott Mead, )
    Re: Scalability in postgres  (Fabrix, )
   Re: Scalability in postgres  (Scott Marlowe, )
 Re: Scalability in postgres  (Scott Marlowe, )
  Re: Scalability in postgres  (Fabrix, )
  Re: Scalability in postgres  (Flavio Henrique Araque Gurgel, )
   Re: Scalability in postgres  (Fabrix, )
    Re: Scalability in postgres  (Scott Marlowe, )
    Re: Scalability in postgres  (Flavio Henrique Araque Gurgel, )
     Re: Scalability in postgres  (Greg Smith, )
      Re: Scalability in postgres  (Grzegorz Jaśkiewicz, )
       Re: Scalability in postgres  (Scott Marlowe, )
       Re: Scalability in postgres  (Scott Marlowe, )
        Re: Scalability in postgres  (Grzegorz Jaśkiewicz, )
         Re: Scalability in postgres  (Scott Marlowe, )
          Re: Scalability in postgres  (Grzegorz Jaśkiewicz, )
           Re: Scalability in postgres  (Scott Marlowe, )
            Re: Scalability in postgres  (Grzegorz Jaśkiewicz, )
             Re: Scalability in postgres  (Scott Marlowe, )
         Re: Scalability in postgres  (Ron Mayer, )
       Re: Scalability in postgres  (Greg Smith, )
        Re: Scalability in postgres  (Scott Mead, )
         Re: Scalability in postgres  (Scott Marlowe, )
         Re: Scalability in postgres  (Fabrix, )
          Re: Scalability in postgres  (Scott Mead, )
      Re: Scalability in postgres  (Fabrix, )
       Re: Scalability in postgres  (Greg Smith, )
      Re: Scalability in postgres  (Scott Carey, )
       Re: Scalability in postgres  (Greg Smith, )
        Re: Scalability in postgres  (Scott Marlowe, )
         Re: Scalability in postgres  (Greg Smith, )
       Re: Scalability in postgres  (Fabrix, )
        Re: Scalability in postgres  (Scott Carey, )
      Re: Scalability in postgres  (James Mansion, )
       Re: Scalability in postgres  ("Kevin Grittner", )
        Re: Scalability in postgres  (Dimitri, )
         Re: Scalability in postgres  ("Kevin Grittner", )
          Re: Scalability in postgres  (Scott Carey, )
           Re: Scalability in postgres  (Robert Haas, )
            Re: Scalability in postgres  (Scott Carey, )
             Re: Scalability in postgres  (Robert Haas, )
              Re: Scalability in postgres  (Scott Carey, )
               Re: Scalability in postgres  (Robert Haas, )
              Re: Scalability in postgres  (, )
               Re: Scalability in postgres  (Robert Haas, )
                Re: Scalability in postgres  (Greg Smith, )
                 Re: Scalability in postgres  (, )
                  Re: Scalability in postgres  (Robert Haas, )
                 Re: Scalability in postgres  (Mark Mielke, )
                  Re: Scalability in postgres  (Greg Smith, )
                   Re: Scalability in postgres  (Robert Haas, )
                 Re: Scalability in postgres  (Craig James, )
          Re: Scalability in postgres  (Dimitri, )
           Re: Scalability in postgres  (Marc Cousin, )
        Re: Scalability in postgres  (James Mansion, )
         Re: Scalability in postgres  ("Kevin Grittner", )
          Re: Scalability in postgres  (Mark Mielke, )
           Re: Scalability in postgres  (, )
            Re: Scalability in postgres  (Mark Mielke, )
             Re: Scalability in postgres  (, )
           Re: Scalability in postgres  ("Kevin Grittner", )
           Re: Scalability in postgres  (Greg Smith, )
          Re: Scalability in postgres  (Scott Carey, )
           Re: Scalability in postgres  ("Kevin Grittner", )
         Re: Scalability in postgres  ("Kevin Grittner", )
 Re: Scalability in postgres  (Jeff Janes, )
  Re: Scalability in postgres  (Tom Lane, )
   Re: Scalability in postgres  (Jeff Janes, )
  Re: Scalability in postgres  ("", )

On Thu, 4 Jun 2009, Robert Haas wrote:

> On Wed, Jun 3, 2009 at 5:09 PM, Scott Carey <> wrote:
>> On 6/3/09 11:39 AM, "Robert Haas" <> wrote:
>>> On Wed, Jun 3, 2009 at 2:12 PM, Scott Carey <> wrote:
>>>> Postgres could fix its connection scalability issues -- that is entirely
>>>> independent of connection pooling.
>
> I think I see the distinction you're drawing here.  IIUC, you're
> arguing that other database products use connection pooling to handle
> rapid connect/disconnect cycles and to throttle the number of
> simultaneous queries, but not to cope with the possibility of large
> numbers of idle sessions.  My limited understanding of why PostgreSQL
> has a problem in this area is that it has to do with the size of the
> process array which must be scanned to derive an MVCC snapshot.  I'd
> be curious to know if anyone thinks that's correct, or not.
>
> Assuming for the moment that it's correct, databases that don't use
> MVCC won't have this problem, but they give up a significant amount of
> scalability in other areas due to increased blocking (in particular,
> writers will block readers).  So how do other databases that *do* use
> MVCC mitigate this problem?  The only one that we've discussed here is
> Oracle, which seems to get around the problem by having a built-in
> connection pooler.  That gets me back to thinking that the two issues
> are related, unless there's some other technique for dealing with the
> need to derive snapshots.

if this is the case, how hard would it be to have threads add and remove
themselves from some list as they get busy/become idle?

I've been puzzled as I've been watching this conversation on what internal
locking/lookup is happening that is causing the problems with idle threads
(the pure memory overhead isn't enough to account for the problems that
are being reported)

David Lang


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