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Sunday, January 27, 2008

Frequently Asked Questions


1) What is a constraint based loading?

When you select this option the power center server orders the target load on a row-by-row basis only.

Edit tasks->properties->select treat source rows as insert.

Edit tasks->config object tab->select constraint based.

If session is configured constraint absed loading when target table receive rows from different sources.The power center server revert the normal loading for those tables but loads all other targets in the session using constraint based loading when possible loading the primary key table first then the foreign key table.

Use the constraint based loading only when the session option treat rows as set to insert.

Constraint based load ordering functionality which allows developers to read the source once and populate parent and child tables in a single process.


2)
Explain incremental aggregation?

When using incremental aggregation you apply captured changes in the source to aggregate calculations in a session.If the source changes only incrementally and you can capture changes you can configure the session to process only those changes. This allows the power center server to update your target incrementally rather than forcing it to process the entire source and recalculate the same data each time you run the session.

You can capture new source data.use incremental aggregation when you can capture new source data much time you run the session.Use a stored procedure on filter transformation only new data.

Incremental changes do not significantly change the target.Use incremental aggregation when the changes do not significantly change the target.If processing the incrementally changed source alters more than half the existing target, the session may not benefit from using incremental aggregation. In this case drop the table and recreate the target with complete source data.


3)
Processing of incremental aggregation?

The first time u run an incremental aggregation session the power center server process the entire source.At the end of the session the power center server stores aggregate data from the session runs in two files, the index file and the data file .The power center server creates the files in a local directory.


Transformations


Q. what is transformation?


Transformation is repository object that generates modifies or passes data.

Transformation is an object which is used for processing or trasforming the data or converting the data into the required business format.


4) what are the type of transformations?

The Transformation which has developed will be stored in the Repository. There are types of trasformations:

1) active
2) passive.


Active transformation can change the number of rows that pass through it.No of output rows less than or equal to no of input rows.


The Following are the Active Transformations--



1) source qualifier Transformation

2) Filter Transformation

3) Joiner Transformation

4) Rank Transformation

5) Router Transformation

6) Aggregator Transformation

7) Normalizer Transformation

8) UpdateStrategy Transformation

9) Sortor Transformation

10) Union Transformation

11) Transaction Control Transformation


Passive transformation
does not change the number of rows.Always no of output rows equal to no of input rows.


The Following are the Passive Transformations---


1) Expression Transformation

2) Sequence Generator Transformation

3) Stored Procedure Transformation

4) XML Source Qualifier Transformation

5) LookUp Transformation


5)
Difference filter and router transformation.

Filter transformation to filter the data only one condition and drop the rows don’t meet the condition.

Drop rows does not store anywhere like session log file..

Router transformation to filter the data based on multiple conditions and give yiou the option to route rows that don’t match to a default group.


6)
what r the types of groups in router transformation?

Router transformation 2 groups ---

1. Input group

2. output groups.


Output groups in 2 types. ---

1. user defined group

2. default group.


7) Difference between expression and aggregator transformation?

Expression transformation calculate the single row values before writes the target.Expression transformation executed by row-by-row basis only.

Aggregator transformation allows you to perform aggregate calculations like max, min,avg…

Aggregate transformation perform calculation on groups.


8) How can u improve the session performance in aggregate transformation?

Use stored input.


9) what is aggregate cache in aggregate transformation?

The aggregate stores data in the aggregate cache until it completes aggregate calculations.When u run a session that uses an aggregate transformation , the informatica server creates index and data caches in memory is process the transformation. If the informatica server requires more space it seores overview values in cache files.


10) Explain joiner transformation?

Joiner transformation joins two related heterogeneous sources residing in different locations or files.


The types of joins in joiner in the joiner transformation--


Normal

Master outer

Detail outer

Full outer



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