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Thread: Sizing Sizing Sizing!!! Pleeeease help!!!!

  1. #1
    Join Date
    Oct 2000


    We are migrating our Oracle DB to a new faster NT server. I am creating the db from scratch and will do an import of the existing db on the cutoverdate. But I need to know how to size...
    #1 Rollback segements and how many

    #2 Redo logs and how many

    #3 How should I size the default initial extents and next extents for the tablespaces I am creating.


  2. #2
    Join Date
    Oct 2000

    Can you post some of the characteristics of your database?

    For example,

    1. How many concurrent users?
    2. How many concurrent transactions?
    3. How big are the transactions?
    4. How big is the largest transaction?

    5. How much activity on your database?
    6. At what rate do you use redo logs now?
    7. What are your backup and recovery requirements?

    David Knight
    OCP DBA 8i, 9i, 10g

  3. #3
    Join Date
    Nov 2000
    # 2 ----> Atleast 2, but my experience shows atleast 3 and then it depends on how you fill your redologs with transactions and how frequently you are archiving your logs and how fast archiving goes.

    # 3 -----> Determine the volume of data, how the data will grow in tables in the tablespace. You should not oversize extents as it would keep unused space.

  4. #4
    Join Date
    Apr 2001
    Louisville KY
    1 -- Used to be 4-8, modern thought, 1 per concurrent user

    2-- How many mount points/controllers? Anyway, at least 3 duplexed (total 6 files), maybe triplexed (9 files in 3 groups). Somewhat depending on update activitiy, recovery time, etc. Spread them over as many controllers as possible. More groups may be needed, depending on archiving and speed for recovery.

    3- Depends on transaction mix. Baseline is minimum io buffer size for your platform. If mostly heavy OLTP (small, quick xacts), then better with smaller extents, suggest at least 1 io buffer. If heavy OLAP (table scans etc), then large extents to bring more data into the SGA at a time.
    Joseph R.P. Maloney, CSP,CDP,CCP
    'The answer is 42'

  5. #5
    Join Date
    Jul 2000
    It would be better if u could also tell ur DB Size now...

    For any DB ,
    u need to have atleast 2 or 3 control files placed in different physical disks and not just in logical partitions which could be in the single physical disk..

    Reason: Even if one hard disk goes for a toss it will be possibly to rebuild the DB with the other control file on another disk.

    REdo Logs:
    HAve atleast 5 redo logs with 10MB size with 2 members each (mirroring)... THis will be very useful for recoveries...
    Note: 10MB may be higher or lesser for ur DB... i am just giving u very general idea...

    Rollback Segs:
    HAve atleast 5-6 rollbacks segs , keep it as smaller say with 5MB and min extents 2-5 for OLTP application.
    Incase of higher batch processing then have bigger segs with say 50MB - 100MB ( this is purely based on ur application)
    Note: Don't forget have enough space in ur rollback tablespace...

    i hope this help you...

  6. #6
    Join Date
    Oct 2000
    The DB is 9 GB, it is running on NT with hardware raid 5 on 4 disks partitioned into a C (os loaded on this drive) and D (Oracle is loaded on this drive). With the raid 5 I cant control which physical disk the control files are on. I also wont be able to seperate my Indexes onto a seperate drive.

    I cant really tell the size of the transactions because there are 5 different apps running against this instance and each app does many different type of transactions.

    It is not a 24x7 shop so I do a cold backup every night and I will have archive logging turned off. I want my redo logs to be big enough to recover at the end of the day without losing more than an hour or two a day.

  7. #7
    Join Date
    Mar 2001

    I have one production database allmost similiar to the size of yours

    1A ) Have six rollback segments size about approx 40 MB each
    1B ) Have one Big Single rollback segment about approx 500 MB.This is very usefull when you are importing into the new database

    The best thing when you are taking an export make the biggest rollback segment online and the rest of the rollback segment offline so that when you import it will make only the biggest rollback segment online and you will not end up with errors during full import.

    2) Have three groups of Redo log files with two members

    3) Depending on the transactions you will need to size your initial extent and next extent for tablspaces


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