Oracle-L: RE: What block size are you using for your new 9i data warehouse?

From: <Cherie_Machler_at_gelco.com>
Date: Fri, 26 Apr 2002 11:33:33 -0800
Message-ID: <F001.00450F02.20020426113333@fatcity.com>

Gaja,

Thanks for this enlightening and helpful reply.

Cherie

                                                                                                                   
                    Gaja Krishna                                                                                   
                    Vaidyanatha          To:     Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>       
                    <oraperfman_at_ya       cc:                                                                       
                    hoo.com>             Subject:     RE: What block size are you using for your new 9i data       
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                    root_at_fatcity.c                                                                                 
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                    04/26/02 11:48                                                                                 
                    AM                                                                                             
                    Please respond                                                                                 
                    to ORACLE-L

All,

Something to keep in mind regardless of whether you are using 9i or not. This issue becomes more relevant in 9i with "multiple block sizes" for different tablespaces.

You always want to ensure that your DB_BLOCK_SIZE = File System Block Size. This is to avoid wasted I/O and also the case where the "read ahead algorithm" is triggered accidentally, when 1 Database Block results in multiple file system blocks being read from disk.

If your application performs range scans, there is a high possibility that multiple "single database block" read requests to a set of contiguous blocks, may result in the "read ahead algorithm" performing 128K or 256K pre-fetches, even though your application may have not required all 128K or 256K.

This problem is rampant on ufs file systems where the default block size is 512 bytes, and with a 8K DB_BLOCK_SIZE, it takes 16 file system blocks to store 1 DB block on disk. However, even if you have advanced file systems and have a 1-is-to-2 ratio of DB block is-to FS blocks, you are still in danger of overloading your I/O sub-system, "under the right conditions".

If you are using a volume manager product such as Veritas, and if your version of the volume manager supports "dynamic file system block sizing" based on size of the file system or the files themselves, please pay close attention to that detail and make sure that the file system block size does not exceed the database block size (based on the size of the file system).

Best regards,

Gaja

Johnson Poovathummoottil <joni_65_at_yahoo.com> wrote:
> We too have a data warehouse close to 500GB in size.
> We upgraded the OS solaris 2.8 and our block size is
> 16K. All our data and index tablespaces datafiles
> are
> spread across 20 files systems whose disks are on
> EMC
> storage. We too user veritas volume manager. File
> systems use four 9 GB disks whaich are raid S and
> software stripe uinit size of 256 KB.
>
> reasons
> 16K block size as we have many full table scan ans
> sequential reads.
> 256 KB stripe unit size because we have set the
> db_file_multi_block_read_count to 64(1MB)
>
> we are moving to a sun fire 15K machine soon and
> then
> the we will go to 9i 64 bit.
>
> --- "Toepke, Kevin M" <ktoepke_at_trilegiant.com>
> wrote:
> > Cherie:
> >
> > If you are using Oracle 9i, you can use mutliple
> > block sizes! You still
> > create your database with a default block size,
> but
> > each tablespace (except
> > system) can have a block size different from the
> > default.
> >
> > Valid blocksizes are limited by OS, but they range
> > from 2K to 32k.
> >
> > Check out the 9i docs for CREATE TABLESPACE for
> more
> > info.
> >
> > Caver
> >
> > -----Original Message-----
> > Sent: Thursday, April 25, 2002 11:24 AM
> > To: Multiple recipients of list ORACLE-L
> >
> >
> >
> > We are building a new version 9.0.1 data warehouse
> > on Sun Solaris 2.6
> > migrating to Solaris 2.8. We will be using
> striped
> > disk that is striped
> > using Veritas Volume Manager on EMC disk.
> >
> > The datawarehouse will be about 200 Gig. It will
> > be written to throughout
> > the day.
> >
> > To this point, almost all of our databases have
> been
> > created with an 8k
> > block size. i'm not sure if that blocksize is
> > optimal anymore. With 9i,
> > what block sizes are people using in the field
> > nowadays for data
> > warehouses?
> >
> > Also, if you use striped disk, what stripe size
> are
> > you using and why?
> >
> > Thanks for weighing in on this topic.
> >
> > Cherie Machler
> > Oracle DBA
> > Gelco Information Network
> >
> > --
> > Please see the official ORACLE-L FAQ:
> > http://www.orafaq.com
> > --
> > Author:
> > INET: Cherie_Machler_at_gelco.com
> >
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> Author: Johnson Poovathummoottil
> INET: joni_65_at_yahoo.com
>
> Fat City Network Services -- (858) 538-5051 FAX:
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Gaja Krishna Vaidyanatha
Director, Storage Management Products,
Quest Software, Inc.
Co-author - Oracle Performance Tuning 101 http://www.osborne.com/database_erp/0072131454/0072131454.shtml

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  INET: Cherie_Machler_at_gelco.com

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Received on Fri Apr 26 2002 - 14:33:33 CDT