Re: Weird XFS WAL problem

От: Kevin Grittner
Тема: Re: Weird XFS WAL problem
Дата: ,
Msg-id: 4C08D7070200002500031F66@gw.wicourts.gov
(см: обсуждение, исходный текст)
Ответ на: Re: Weird XFS WAL problem  (Bruce Momjian)
Ответы: Re: Weird XFS WAL problem  (Bruce Momjian)
Re: Weird XFS WAL problem  (Greg Smith)
Список: pgsql-performance

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Random Page Cost and Planner  (David Jarvis, )
 Re: Random Page Cost and Planner  (David Jarvis, )
 Re: Random Page Cost and Planner  ("Kevin Grittner", )
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   Re: Random Page Cost and Planner  (Tom Lane, )
    Re: Random Page Cost and Planner  (David Jarvis, )
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      Re: Random Page Cost and Planner  (David Jarvis, )
   Re: Random Page Cost and Planner  (Rob Wultsch, )
    Re: Random Page Cost and Planner  (David Jarvis, )
     Re: Random Page Cost and Planner  (, )
   Re: Random Page Cost and Planner  ("Kevin Grittner", )
    Re: Random Page Cost and Planner  (David Jarvis, )
     Re: Random Page Cost and Planner  (David Jarvis, )
 Re: Random Page Cost and Planner  (, )
  Re: Random Page Cost and Planner  (David Jarvis, )
 Re: Random Page Cost and Planner  (David Jarvis, )
  Re: Random Page Cost and Planner  (Cédric Villemain, )
   Re: Random Page Cost and Planner  (David Jarvis, )
    Re: Random Page Cost and Planner  (Cédric Villemain, )
     Weird XFS WAL problem  (Craig James, )
      Re: Weird XFS WAL problem  (Mark Kirkwood, )
       Re: Weird XFS WAL problem  (Craig James, )
        Re: Weird XFS WAL problem  (Matthew Wakeling, )
         Re: Weird XFS WAL problem  ("Kevin Grittner", )
          Re: Weird XFS WAL problem  (Greg Smith, )
           Re: Weird XFS WAL problem  ("Kevin Grittner", )
            Re: Weird XFS WAL problem  (Scott Marlowe, )
             Re: Weird XFS WAL problem  ("Kevin Grittner", )
             Re: Weird XFS WAL problem  (Greg Smith, )
              Re: Weird XFS WAL problem  (Scott Marlowe, )
              Re: Weird XFS WAL problem  ("Kevin Grittner", )
              Re: Weird XFS WAL problem  (Matthew Wakeling, )
           Re: Weird XFS WAL problem  (Bruce Momjian, )
            Re: Weird XFS WAL problem  ("Kevin Grittner", )
             Re: Weird XFS WAL problem  (Bruce Momjian, )
              Re: Weird XFS WAL problem  ("Kevin Grittner", )
               Re: Weird XFS WAL problem  (Bruce Momjian, )
                Re: Weird XFS WAL problem  ("Kevin Grittner", )
                 Re: Weird XFS WAL problem  (Bruce Momjian, )
                 Re: Weird XFS WAL problem  (Greg Smith, )
                  Re: Weird XFS WAL problem  (Bruce Momjian, )
        Re: Weird XFS WAL problem  (Greg Smith, )
      Re: Weird XFS WAL problem  (Merlin Moncure, )
      Re: Weird XFS WAL problem  (Greg Smith, )
  Re: Random Page Cost and Planner  (Bryan Hinton, )
   Re: Random Page Cost and Planner  (David Jarvis, )

Bruce Momjian <> wrote:
> Kevin Grittner wrote:

>> Any decent RAID controller will ensure that the drives themselves
>> aren't using write-back caching.  When we've mentioned write-back
>> versus write-through on this thread we've been talking about the
>> behavior of the *controller*.  We have our controllers configured
>> to use write-back through the BBU cache as long as the battery is
>> good, but to automatically switch to write-through if the battery
>> goes bad.
>
> OK, good, but when why would a BBU RAID controller flush stuff to
> disk with a flush-all command?  I thought the whole goal of BBU
> was to avoid such flushes.

That has been *precisely* my point.

I don't know at the protocol level; I just know that write barriers
do *something* which causes our controllers to wait for actual disk
platter persistence, while fsync does not.

The write barrier concept seems good to me, and I wish it could be
used at the OS level without killing performance.  I blame the
controller, for not treating it the same as fsync (i.e., as long as
it's in write-back mode it should treat data as persisted as soon as
it's in BBU cache).

-Kevin


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