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

От: Joseph S
Тема: Re: What exactly is postgres doing during INSERT/UPDATE ?
Дата: ,
Msg-id: 4A9ADAAD.1050900@selectacast.net
(см: обсуждение, исходный текст)
Ответ на: Re: What exactly is postgres doing during INSERT/UPDATE ?  (Scott Marlowe)
Ответы: Re: What exactly is postgres doing during INSERT/UPDATE ?  (Jeff Janes)
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, )

I've already learned my lesson and will never use raid 5 again.  The
question is what I do with my 14 drives. Should I use only 1 pair for
indexes or should I use 4 drives?  The wal logs are already slated for
an SSD.

Scott Marlowe wrote:
> On Sat, Aug 29, 2009 at 2:46 AM, Greg Stark<> wrote:
>> On Sat, Aug 29, 2009 at 5:20 AM, Luke Koops<> wrote:
>>> Joseph S Wrote
>>>> If I have 14 drives in a RAID 10 to split between data tables
>>>> and indexes what would be the best way to allocate the drives
>>>> for performance?
>>> RAID-5 can be much faster than RAID-10 for random reads and writes.  It is much slower than RAID-10 for sequential
writes,but about the same for sequential reads.  For typical access patterns, I would put the data and indexes on
RAID-5unless you expect there to be lots of sequential scans. 
>> That's pretty much exactly backwards. RAID-5 will at best slightly
>> slower than RAID-0 or RAID-10 for sequential reads or random reads.
>> For sequential writes it performs *terribly*, especially for random
>> writes. The only write pattern where it performs ok sometimes is
>> sequential writes of large chunks.
>
> Note that while RAID-10 is theoretically always better than RAID-5,
> I've run into quite a few cheapie controllers that were heavily
> optimised for RAID-5 and de-optimised for RAID-10.  However, if it's
> got battery backed cache and can run in JBOD mode, linux software
> RAID-10 or hybrid RAID-1 in hardware RAID-0 in software will almost
> always beat hardware RAID-5 on the same controller.
>


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