RE: Lost appendix: Space Estimations for Schema Objects
- From: DENNIS WILLIAMS <DWILLIAMS@xxxxxxxxxxxxx>
- To: "'oracle-l@xxxxxxxxxxxxx'" <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 16 Jun 2004 13:28:11 -0500
Leslie
You can also do some Googling to find other formula variations. As was
mentioned, loading a test table to get good estimates of column sizes is the
best way. As you mentioned, uncertain row count estimates introduces a great
deal of uncertainty in your calculations. But then you can simply point out
to your client that your estimates can only be as accurate as the
information you are provided.
Dennis Williams
DBA
Lifetouch, Inc.
dwilliams@xxxxxxxxxxxxx
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Leslie Tierstein
Sent: Wednesday, June 16, 2004 1:27 PM
To: oracle-l@xxxxxxxxxxxxx
Cc: peter.sharman@xxxxxxxxxx; lex.de.haan@xxxxxxxxxxxxxx
Subject: RE: Lost appendix: Space Estimations for Schema Objects
Applying the formulas as documented in Oracle 8, and comparing the results
to an actual Oracle 8i database (a data warehouse; I'm interested only in 8
fact tables ranging in size from 10 million to 500 million rows; the 9i
database is for a new client, and is the reason for this exercise) yields
the following:
- Table estimates for non-partitioned tables are within 10% (uniformly lower
for the estimate than the actual) of the actual
- But the table estimates don't take into account partitioned tables, which
are farther off
- B-Tree index estimates were modified to reflect the changed size of the
ROWID; most are still within 10% deviation from the actual
- We're still looking at the bitmap indexes (determining cardinality) and
the local partitioned indexes
More problematic is actually determining how many rows are going to be in
each fact table -- both at startup and at 6 month intervals.
Unfortunately, we're not going to 10g any time soon, so I can't use the EM
facility Lex mentioned.
Leslie
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Pete Sharman
Sent: Tuesday, June 15, 2004 1:42 PM
To: oracle-l@xxxxxxxxxxxxx
Cc: Peter Ross Sharman
Subject: RE: Lost appendix: Space Estimations for Schema Objects
Leslie
It was taken out because there are so many variations and permutations
possible that a generic formula is never going to be realistic. The only
realistic way to get space estimations is to load a "typical" set of data
(whatever that is) and then extrapolate to Production sizes, based on
history and so on.
Pete
"Controlling developers is like herding cats."
Kevin Loney, Oracle DBA Handbook
"Oh no, it's not. It's much harder than that!"
Bruce Pihlamae, long-term Oracle DBA
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Leslie Tierstein
Sent: Wednesday, 16 June 2004 3:02 AM
To: oracle-l
Subject: Lost appendix: Space Estimations for Schema Objects
The Oracle 8.0 documentation had an Appendix A to the "Oracle Server
Administrator's Guide" on "Space Estimations for Schema Objects". It gave
formulas for approximating the amount of disk space that would be taken up
by tables and indexes, taking into account block size, init trans, pct free,
etc. The appendix seems to have vanished in the 9i documentation -- at least
I can't find it.
Does anyone know if/where this information still exists, either in the
Oracle documentation set or some other documentation?
Thanks,
Leslie
Leslie Tierstein
Senior Consultant
Vision Chain, Inc.
The first software to power the demand data network
phone: 202-261-3549
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