Re: What exactly is postgres doing during INSERT/UPDATE ?

От: Aidan Van Dyk
Тема: Re: What exactly is postgres doing during INSERT/UPDATE ?
Дата: ,
Msg-id: 20090831144809.GF12444@oak.highrise.ca
(см: обсуждение, исходный текст)
Ответ на: Re: What exactly is postgres doing during INSERT/UPDATE ?  (Merlin Moncure)
Список: pgsql-performance

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What exactly is postgres doing during INSERT/UPDATE ?  (Joseph S, )
 Re: What exactly is postgres doing during INSERT/UPDATE ?  (Pierre Frédéric Caillaud<>, )
 Re: What exactly is postgres doing during INSERT/UPDATE ?  (Greg Smith, )
  Re: What exactly is postgres doing during INSERT/UPDATE ?  (Scott Marlowe, )
   Re: What exactly is postgres doing during INSERT/UPDATE ?  (Joseph S, )
    Re: What exactly is postgres doing during INSERT/UPDATE ?  (Luke Koops, )
     Re: What exactly is postgres doing during INSERT/UPDATE ?  (Greg Stark, )
      Re: What exactly is postgres doing during INSERT/UPDATE ?  (Scott Marlowe, )
       Re: What exactly is postgres doing during INSERT/UPDATE ?  (Merlin Moncure, )
        Re: What exactly is postgres doing during INSERT/UPDATE ?  (Greg Stark, )
        Re: What exactly is postgres doing during INSERT/UPDATE ?  (Mark Mielke, )
         Re: What exactly is postgres doing during INSERT/UPDATE ?  (Merlin Moncure, )
          Re: What exactly is postgres doing during INSERT/UPDATE ?  (Greg Stark, )
           Re: What exactly is postgres doing during INSERT/UPDATE ?  (Merlin Moncure, )
            Re: What exactly is postgres doing during INSERT/UPDATE ?  (Aidan Van Dyk, )
       Re: What exactly is postgres doing during INSERT/UPDATE ?  (Joseph S, )
        Re: What exactly is postgres doing during INSERT/UPDATE ?  (Jeff Janes, )
         Re: What exactly is postgres doing during INSERT/UPDATE ?  ("Kevin Grittner", )
          Re: What exactly is postgres doing during INSERT/UPDATE ?  (Scott Marlowe, )
      Re: What exactly is postgres doing during INSERT/UPDATE ?  (David Rees, )
  Re: What exactly is postgres doing during INSERT/UPDATE ?  (Joseph S, )
 Re: What exactly is postgres doing during INSERT/UPDATE ?  (Jeff Janes, )
  Re: What exactly is postgres doing during INSERT/UPDATE ?  (Merlin Moncure, )
   Re: What exactly is postgres doing during INSERT/UPDATE ?  (Jeff Janes, )

* Merlin Moncure <> [090831 10:38]:

> I agree, that's good analysis.  The main point I was making was that
> if you have say a 10 disk raid 5, you don't involve 10 disks, only
> two...a very common misconception.  I made another mistake that you
> didn't catch: you need to read *both* the data drive and the parity
> drive before writing, not just the parity drive.
>
> I wonder if flash SSD are a better fit for raid 5 since the reads are
> much cheaper than writes and there is no rotational latency.  (also,
> $/gb is different, and so are the failure cases).

The other thing that scares me about raid-5 is the write-hole, and the
possible delayed inconsistency that brings...

Again, hopefully mitigated by a dependable controller w/ BBU...

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

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