RE: Sizing Indexes - URGENT

From: DENNIS WILLIAMS <DWILLIAMS_at_LIFETOUCH.COM>
Date: Mon, 17 Mar 2003 06:03:55 -0800
Message-ID: <F001.0056B8BB.20030317060355@fatcity.com>

Jai

    I couldn't follow all the details of your calculation. I would have expected to see a calculation for the number of rows per block. Once you know how many rows you can pack into a block, then you can estimate the number of blocks you will need. Maybe you have it in there and I just couldn't see it this early on a Monday morning.

   As a sanity check, do the simple bytes/row * no. of rows and make sure you are reasonably close.

   Looking at the bigger picture, I wouldn't get too picky about this. Usually your number of rows is only a guess anyway. Spend your time looking at LMT and uniform extents. Oracle is trying to save us from time-consuming tasks like this. :-)

Dennis Williams
DBA, 40%OCP, 100% DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----

Sent: Sunday, March 16, 2003 10:09 PM
To: Multiple recipients of list ORACLE-L

Dear All,

I have a task on hand to size a database for our application. I have used the Oracle rule to find out the rowsize of rows in a table.

1. Space available for the data (SAD) = data block size - block header size = db_block_size - kcbh - ub4 - ktbbh - (initrans
   -1)* ktbit - kdbh
   
2. Available Data Space (ADS) = ceil(SAD * (1-pctfree/100)) - kdbt
3. Space used per row (SPR) = (Total size of the columns data length) + (1 byte per column with length < 250 )+ (3 * 1 byte per column with length >= 250)
4. Row Size (ROWSZ) = 3 * ub1 + SPR
5. Space used per row(SPROW) = max(ub1 * 3 + ub4 + sb2, ROWSZ) + sb2
6. Total Size of the table = Expected Number of records * SPROW

I hope this formula is correct.

How can I do the sizing of indexes. Shouldn't I take into account the 10 bytes consumed by the ROWID pseudocolumn apart from the column(s) that are indexed ?

TIA for all your help.

Best Regards
Jai

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Author: DENNIS WILLIAMS
  INET: DWILLIAMS_at_LIFETOUCH.COM

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