Обсуждение: seqential vs random io

- DAP
----------------------------------------------------------------------------------
David Parker    Tazz Networks    (401) 709-5130
 

David Parker wrote:
> I just got a question from one our QA guys who is configuring a RAID 10
> disk that is destined to hold a postgresql database. The disk
> configuration procedure is asking him if he wants to optimize for
> sequential or random access. My first thought is that random is what we
> would want, but then I started wondering if it's not that simple, and my
> knowledge of stuff at the hardware level is, well, limited.....
>
> If it were your QA guy, what would you tell him?
>
> - DAP

Random. Sequential is always pretty fast, it is random that hurts.

The only time I would say sequential is if you were planning on
streaming large files (like iso images) with low load.

But for a DB, even a sequential scan will probably not be that much data.

At least, that's my 2c.

John
=:->

David,

> > I just got a question from one our QA guys who is configuring a RAID 10
> > disk that is destined to hold a postgresql database. The disk
> > configuration procedure is asking him if he wants to optimize for
> > sequential or random access. My first thought is that random is what we
> > would want, but then I started wondering if it's not that simple, and my
> > knowledge of stuff at the hardware level is, well, limited.....
> >
> > If it were your QA guy, what would you tell him?

Depends on the type of database.  OLTP or Web == random access.  Data
Warehouse == sequential access.

--
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco

I would tell him to go for the random, which is what most DBs would be by nature. What you need to understand will be
thecache parameters, read/write cache amount, and stripe size, depending on your controller type and whatever it
defaultsto on these things.
 
 
Thanks,
Anjan

    -----Original Message----- 
    From: David Parker [mailto:dparker@tazznetworks.com] 
    Sent: Mon 5/23/2005 4:58 PM 
    To: pgsql-performance@postgresql.org 
    Cc: 
    Subject: [PERFORM] seqential vs random io
    
    
    I just got a question from one our QA guys who is configuring a RAID 10 disk that is destined to hold a postgresql
database.The disk configuration procedure is asking him if he wants to optimize for sequential or random access. My
firstthought is that random is what we would want, but then I started wondering if it's not that simple, and my
knowledgeof stuff at the hardware level is, well, limited.....
 
     
    If it were your QA guy, what would you tell him?

    - DAP
    ----------------------------------------------------------------------------------
    David Parker    Tazz Networks    (401) 709-5130