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  1. #1
    Join Date
    Dec 2003
    Posts
    1,074

    Unanswered: Space requirements

    We've converted several systems from WANG to Oracle, and we were hoping to see a pattern between the amount of space required on the WANG, and the space now required in Oracle.

    We got some whacked out numbers, though. What could explain this kind of disparity, the index storage differences?

    Code:
    ORACLE  WANG
    55M      39.52 MB   39.17% diff
    31M      24.14 MB   28.42% diff
    104M     89.62 MB   16.05% diff
    687M    755.12 MB   -9.02% diff 
    364M    252.63 MB   44.08% diff
    28M      27.69 MB    1.12% diff

  2. #2
    Join Date
    Nov 2002
    Posts
    833
    consider next extent sizes which may be larger chunks in oracle than in your WANG envoionment. If a next extent is requested the default chunk is allocated , and for the current final extent it may be nearly empty ... and what are your settings for pctincrease?

  3. #3
    Join Date
    Apr 2003
    Location
    Greenville, SC (USA)
    Posts
    1,155
    You can check the highwater mark in the tables to see the unused space
    Attached is a script that I use ... Change the OWNER in the script and
    run from sqlplus ... It will show the total space and the unused space for
    all tables with a size > 1meg ... (dbms_output.put_line) ...
    This can easily be modified to do the same for indexes within a schema also...

    HTH
    Gregg
    Attached Files Attached Files

  4. #4
    Join Date
    Mar 2002
    Location
    Reading, UK
    Posts
    1,137
    Also check out your pctfree & pctused (only for tables) as these can dramatically alter storage requirements. Indexes can be shrunk with the compress clause sometimes as can tables though you may have adverse affects if you dont test it properly.

    Alan

  5. #5
    Join Date
    Dec 2003
    Posts
    1,074
    At this point we're taking advantage of Oracle's automatic space management, creating tablespaces like the following, and not specifying any of the parameters mentioned above when creating a table:

    Code:
    create tablespace ib_data
    datafile '/u02/oradata/dev/ib_data01.dbf' size 140M
    autoextend on next 1M maxsize unlimited
    extent management local autoallocate
    segment space management auto;
    I quoted OEM as far as space used for any particular system, as we're devoting 1 tablespace per system for both indexes and tables.

    I am guessing here, but since we performed a dataload from WANG extracts prior to retrieving these numbers, there shouldn't be too much unused space in OEM's calculations right off the bat, maybe?

    -Chuck

  6. #6
    Join Date
    Apr 2003
    Location
    Greenville, SC (USA)
    Posts
    1,155
    I would still run the scripts to see what the size was (if I really wanted to know what the differences was) ... As well as checking pctfree as AlanP stated... If pctfree =40, then Oracle is only going to load data in 60% of a given datablock leaving the additional 40 percent for DML. I don't have
    a clue as to how WANG manages their datablocks, but if they fill them, then
    pctfree is probably your biggest reason

    HTH
    Gregg

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