Significance of Cost in CBO

A query with
1)cost=7563 bytes=35,635 cardinality=9837
After query restructure
2) cost=10,390 bytes 25,589 cardinality=6783
which query will perform better ?
if second query performs better what is the significance of cost
Any help will be greatly appreciated
Thanks !

Hi!
Cost is execution time expressed in some arcane measure.
The key point to understand is that the actual number is totally dependent on the accuracy of the formulas and calculations built into the optimizer.
Thus, if the optimizers guess is "perfect", then a lower cost often (far from always) equals reduced runtime.
Likewise, if the optimizer is dead wrong and thinks your query will return 1 row, when in reality it returns 1,000,000 rows, the cost is most likely wrong.
/ Ronnis

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What is the significance of "cost" column in explain plan

Hi,
Can anyone explain what is the meaning of the values which we get in the cost column in the explain plan..For Ex : Cost : 4500 . What does this value mean...and is it measured in which form of units...i mean seconds,nanoseconds etc

kingfisher,
Ok one more link for you but I shall quote the text also here,
http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/optimops.htm#i82005
The cost is an estimated value proportional to the expected resource use needed to execute the statement with a particular plan. The optimizer calculates the cost of access paths and join orders based on the estimated computer resources, which includes I/O, CPU, and memory.
And few paragraphs down,
13.4.1.3.3 Cost
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The access path determines the number of units of work required to get data from a base table. The access path can be a table scan, a fast full index scan, or an index scan. During table scan or fast full index scan, multiple blocks are read from the disk in a single I/O operation. Therefore, the cost of a table scan or a fast full index scan depends on the number of blocks to be scanned and the multiblock read count value. The cost of an index scan depends on the levels in the B-tree, the number of index leaf blocks to be scanned, and the number of rows to be fetched using the rowid in the index keys. The cost of fetching rows using rowids depends on the index clustering factor. See "Assessing I/O for Blocks, not Rows".
The join cost represents the combination of the individual access costs of the two row sets being joined, plus the cost of the join operation.
Now I guess if you read this part, it should be pretty clear what cost is.Cost is an evlaution of the resource that is estimated by Oracle for every step incurred in the uery execution.There are no of steps and each may involve doing IO,consuming CPU and/or using memory.Cost is a factor which oracle uses combining all of these 3 (depending on the version) together to propose the work done or expected to be done in exeuting a query.So this actualy should represent the time spent exactly on each and every step.That's what the objective frm cost is.But at the moment,this is not there.There amy be a situation that cost is shown as very high but query is working fine.There are woraround which can bring the cost down for example using and tweaking optimizer_index_cost_adj parameter , we can propose oracle regarding our indexes and it may pick up lesser cost evaluation.What is mentioned is that this model is becoming more and more mature and in the next releases, we may see that cost is representing exactly the time that we would spend inthe query.At the moment,its not there.So as Chris mentioned,Tuning for low cost only is not a good way.
I suggest you grab a copy of JL's book.He has explained it much better in his book.
Hope I said some thing useful.
Aman....

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What is the most cost efficient way to transfer 35mm slide images to my iMac hard drive?

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Sender Cost Element Group role in Assessment Cost Element Cycle

Hello,
We have an assessment cycle as below:-
Assessment Cost Element - 6000000
Sender Rule - Fixed Amount
Receiver Rule - Variable Portions
Sender Cost Center - 1000
Sender Cost Element Group - ABCD
Receiver Order Group - XYZS
Sender Values - 2,00,000 USD - Cost Center 1000
Cost Element Group in Receiver Tracing Factor tab - EFGH,
When I see the line item report of sender cost center 1000, I am able to see the total value as 2.00,000 USD credited, but I am not sure about the role of Sender cost element group ABCD in this situation.
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Please advise.
Thanks
Tapan

Hi Tapan,
When you have selected in sender rule fixed amount then the system will transfer that amount to the receiver cost center specified irrespective of the total amount of cost element group existing in the sender cost center. There is no significance of cost element group mentioned in the sender rule then.
The role of the receiver cost element group in the tracing factor is used to apportion the amount of the sender according to the expenses existing on the orders in your case.
Regards,
Divraj

QM PLant settings - Cost center

HI QM Gurus,
In the inspection lot completion tab for QM Plant settings in customization
we have two feilds
Cost Center - Scrap and Destruction
What is the significance of Cost center feilds in QM Plant settings?
What will happen if I do not use any of these feilds?
Are they only for reporting purpose?
I believe for each movement type we define one cost center.
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Hi Jeevan,
You can post quantities of material from an inspection lot to the following destinations:
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**Process Flow**
The planned quantity of the order is 10 units. The yield is 8 pieces and the scrap quantity is 2 pieces.
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Cost elemnt tab in assesment ksu7

hi
all
what is the use of cost element field in the sender tab of assessment
what i understood we cam mention the cost element which caries the cost
iam no talking about assessment coastline
i wnat to know significance of cost Clement below the cost center in the sender tab

Hello,
Costs in the sender cost center will be represented by cost element. This cost will be moved from sender cost center to receiver cost center. To the receiver side it will be written to secondary cost elements. However, there is no drill down is possible on the receiver side.
Please read the following for further clarification.
ASSESSMENT =========== Assessment was created to transfer primary and secondary costs from a sender cost center to receiving controlling objects. During assessment, cost center or business processes can be used as senders. The receivers for an assessment can be a cost center, WBS element, internal order, cost object, or a business process. You can restrict the number of receiver categories in customizing. Primary and secondary posting are allocated at the end of the period by the user-defined key. During assessment, the original cost elements are summarized into assessment cost elements (secondary cost element category = 42). As the system writes fewer total records, the assessment has a better performance than periodic reposting and distribution. The system does not display the original cost elements in the receivers. Therefore, assessment is useful if the cost drilldown for the receiver is not important. Similar to distribution, the partner is updated in the totals record during distribution You can reverse assessments as often as required. You use the Cycle-Segment method to define sender-receiver relationships.
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Aladane wrote:
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How to calculate the COGM for ETO

Hi Gurus,
In my client follows Discrete Manufacturing ETO (Engineering to Order),
Some Orders showed std price for COGM
In some Orders it showed planned Price for COGM
In some Orders it showed Other Value for COGM.
Still i am confusing regarding for this issue, so could you clarification how the process going on ETO Order.....
Thanks,
Chandrababu.B
Edited by: Chandrababu Naidu on May 17, 2011 3:15 PM
Edited by: Chandrababu Naidu on May 17, 2011 3:19 PM

I agree with you. But, the optimizer's produced best_plan may not be perfect for some queries. Search in asktom site regarding cost of CBO. There is a big debate on this in one of the oracle list group by an oracle experts. Remember this could note be the same for all qureies. I am just warning you that, a low cost not gurantee that run father than a higher cost value.
SJH
OCP DBA

Significance of Cost in CBO

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