Re: moving pg_xlog -- yeah, it's worth it!

From: Aidan Van Dyk
Subject: Re: moving pg_xlog -- yeah, it's worth it!
Date: ,
Msg-id: 20100211180421.GE14128@oak.highrise.ca
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In response to: Re: moving pg_xlog -- yeah, it's worth it!  (Alvaro Herrera)
Responses: Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner")
List: pgsql-performance

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moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
 Re: moving pg_xlog -- yeah, it's worth it!  (Jesper Krogh, )
  Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
   Re: moving pg_xlog -- yeah, it's worth it!  (Amitabh Kant, )
    Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
   Re: moving pg_xlog -- yeah, it's worth it!  (Bruce Momjian, )
    Re: moving pg_xlog -- yeah, it's worth it!  (Scott Marlowe, )
   Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
    Re: moving pg_xlog -- yeah, it's worth it!  (Alvaro Herrera, )
     Re: moving pg_xlog -- yeah, it's worth it!  (Aidan Van Dyk, )
      Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
 Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
  Re: moving pg_xlog -- yeah, it's worth it!  (Alvaro Herrera, )
   Re: moving pg_xlog -- yeah, it's worth it!  (Alvaro Herrera, )
    Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
     Re: moving pg_xlog -- yeah, it's worth it!  (Alvaro Herrera, )
  Re: moving pg_xlog -- yeah, it's worth it!  (Greg Smith, )
   Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
    Re: moving pg_xlog -- yeah, it's worth it!  (Ben Chobot, )

* Alvaro Herrera <> [100211 12:58]:
> Hmm, so maybe the performance benefit is not from it being on a separate
> array, but from it being RAID1 instead of RAID5?

Or the cumulative effects of:
1) Dedicated spindles/Raid1
2) More BBU cache available (I can't imagine the OS pair writing much)
3) not being queued behind data writes before getting to controller
3) Not waiting for BBU cache to be available (which is shared with all data
   writes) which requires RAID5 writes to complete...

Really, there's *lots* of variables here.  The basics being that WAL on
the same FS as data, on a RAID5, even with BBU is worse than WAL on a
dedicated set of RAID1 spindles with it's own BBU.

Wow!

;-)


--
Aidan Van Dyk                                             Create like a god,
                                       command like a king,
http://www.highrise.ca/                                   work like a slave.

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