Re: User concurrency thresholding: where do I look?

От: Tom Lane
Тема: Re: User concurrency thresholding: where do I look?
Дата: ,
Msg-id: 14009.1184867115@sss.pgh.pa.us
(см: обсуждение, исходный текст)
Ответ на: Re: User concurrency thresholding: where do I look?  (Alvaro Herrera)
Ответы: Re: User concurrency thresholding: where do I look?  (Josh Berkus)
Список: pgsql-performance

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User concurrency thresholding: where do I look?  (Josh Berkus, )
 Re: User concurrency thresholding: where do I look?  ("Joshua D. Drake", )
 Re: User concurrency thresholding: where do I look?  (Alvaro Herrera, )
  Re: User concurrency thresholding: where do I look?  (Josh Berkus, )
   Re: User concurrency thresholding: where do I look?  (Tom Lane, )
    Re: User concurrency thresholding: where do I look?  (Alvaro Herrera, )
     Re: User concurrency thresholding: where do I look?  (Tom Lane, )
      Re: User concurrency thresholding: where do I look?  (Josh Berkus, )
       Re: User concurrency thresholding: where do I look?  (Tom Lane, )
        Re: User concurrency thresholding: where do I look?  (Josh Berkus, )
         Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
          Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
          Re: User concurrency thresholding: where do I look?  (Tom Lane, )
           Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
            Re: User concurrency thresholding: where do I look?  (Tom Lane, )
             Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
              Re: User concurrency thresholding: where do I look?  (Tom Lane, )
               Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                Re: User concurrency thresholding: where do I look?  (Tom Lane, )
                 Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                 Re: User concurrency thresholding: where do I look?  (David Boreham, )
                  Re: User concurrency thresholding: where do I look?  (Tom Lane, )
                 Re: User concurrency thresholding: where do I look?  ("Simon Riggs", )
                  Re: User concurrency thresholding: where do I look?  (Tom Lane, )
                   Re: User concurrency thresholding: where do I look?  ("Simon Riggs", )
                    Re: User concurrency thresholding: where do I look?  (Tom Lane, )
                     Re: User concurrency thresholding: where do I look?  ("Simon Riggs", )
                      Re: User concurrency thresholding: where do I look?  (Tom Lane, )
                       Re: User concurrency thresholding: where do I look?  ("Simon Riggs", )
                      Re: User concurrency thresholding: where do I look?  ("Simon Riggs", )
                       Re: User concurrency thresholding: where do I look?  (Tom Lane, )
                        Re: User concurrency thresholding: where do I look?  ("Simon Riggs", )
                        Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                         Re: User concurrency thresholding: where do I look?  (Tom Lane, )
                          Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                           Re: User concurrency thresholding: where do I look?  (Tom Lane, )
                            Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                             Re: User concurrency thresholding: where do I look?  (Tom Lane, )
                              Re: User concurrency thresholding: where do I look?  (Robert Lor, )
                             Re: User concurrency thresholding: where do I look?  ("Simon Riggs", )
                              Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                               Re: User concurrency thresholding: where do I look?  ("Simon Riggs", )
                                Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                                 Re: User concurrency thresholding: where do I look?  (Alvaro Herrera, )
                                  Re: User concurrency thresholding: where do I look?  ("Simon Riggs", )
                                 Re: User concurrency thresholding: where do I look?  ("Simon Riggs", )
                                  Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                                  Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                                   Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                                    Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                                  Re: User concurrency thresholding: where do I look?  (Josh Berkus, )
                                   Re: User concurrency thresholding: where do I look?  ("Jignesh K. Shah", )
                              CLOG Patch  ("Jignesh K. Shah", )
                               Re: CLOG Patch  ("Simon Riggs", )
                                Re: CLOG Patch  ("Jignesh K. Shah", )
                                 Re: CLOG Patch  ("Simon Riggs", )
                           Re: User concurrency thresholding: where do I look?  ("Simon Riggs", )
       Re: User concurrency thresholding: where do I look?  (Greg Smith, )
        Re: User concurrency thresholding: where do I look?  (Josh Berkus, )
     Re: User concurrency thresholding: where do I look?  ("Joshua D. Drake", )
    Re: User concurrency thresholding: where do I look?  (Gregory Stark, )
 Re: User concurrency thresholding: where do I look?  (Greg Smith, )

Alvaro Herrera <> writes:
> Tom Lane wrote:
>> AFAIK you'd get hard failures, not slowdowns, if you ran out of lock
>> space entirely;

> Well, if there still is shared memory available, the lock hash can
> continue to grow, but it would slow down according to this comment in
> ShmemInitHash:

Right, but there's not an enormous amount of headroom in shared memory
beyond the intended size of the hash tables.  I'd think that you'd start
seeing hard failures not very far beyond the point at which performance
impacts became visible.  Of course this is all speculation; I quite
agree with varying the table-size parameters to see if it makes a
difference.

Josh, what sort of workload is being tested here --- read-mostly,
write-mostly, a mixture?

> However I was talking to Josh Drake yesterday and he told me that
> pg_dump was spending some significant amount of time in LOCK TABLE when
> there are lots of tables (say 300k).

I wouldn't be too surprised if there's some O(N^2) effects when a single
transaction holds that many locks, because of the linked-list proclock
data structures.  This would not be relevant to Josh's case though.

            regards, tom lane


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