RE: segment growth
Date: Mon, 7 Apr 2014 15:04:49 -0400
Message-ID: <9287D00721407A4CBDC9925C789DBB6702F9DB7CCA_at_nam-wil-exc-l03.newsamerica.com>
Why do you care about segment growth?
You can add/remove disk at tablespaces level, so I think that forecasting at tablespace level makes sense. I do not use AWR for disk forecasting because the typical retention period is way too short – usually a couple of weeks. I am aware that it could be changed, but I the disk storage associated with a retention increase can be significant if the retention is to be changed to a few months or a couple of years.
You can source your data from the OEM repository (if licensed and used) and/or your own custom repository for capacity and performance data. While there are many ways/techniques for trend analysis, a simple linear regression is a good first step. It is important (as Mark already mentioned) that you do confidence calculations, such as confidence intervals and coefficient of determination (R squared), to insure that the model (linear regression in our case) fits your data. My guess is that for many regular tablespaces, linear regression would be OK.
If the model gives too wide confident interval, dues to lack or data points or significant non-linear patterns, or too low R square, you need to accept that the linear model is not good enough and either do “manual” estimates or employ more powerful trend analysis methods.
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From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Remigiusz Sokolowski
Sent: Wednesday, April 02, 2014 2:18 AM
To: oracle-l
Subject: segment growth
hi,
I have just tried to realize how to count a segment growth trend based on the dba_hits_seg_stat rows. And now I am puzzled:
1. on the metalink I have found the article 1395195.1, which suggests to simply sum the db_block_changes_delta 2. I displayed the data for some particular segment to find out the possible relations between numbers and I would say this is rather the value, which indicates literally the delta of block changes i.e. all the deletes, inserts, updates and not only new blocks - for example because the db_block_changes_delta is always positive and db_block_changes_total always grows 3. So I look at space_used_total assuming this is the total space used by the segment in the moment a snap is taken - and here longer example
current size of the object
object_name | blocks | bytes
ZABBIX.ITEMS 4992 40894464 excerpt from snap values - few subsequent snaps
OBJ_SNAP, SPACE_USED_TOTAL, SPACE_USED_DELTA, 13356 933731 9503
13357 937827 4096
13358 940940 3113
13359 -3277 -3277
13360 737 4014
13361 6062 5325
13362 7045 983
until 13358 all is fine I see the logic ( space_used_total(n)=space_used_total(n-1)+space_used_delta(n) ) but then negative total value (and the logic's gone) - no idea what to think about that. And the main question - how to calculate the segment growth trend in a reliable manner?
Best regards
Remigiusz
--
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Remigiusz Sokolowski <remigiusz.sokolowski_at_nordea.com><mailto:remigiusz.sokolowski_at_nordea.com>
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