Datastage Interview Questions and Answers

56.	What are Active and Passive stages?
	Active Stage : Active stage model the flow of data and provide mechanisms for combining data streams, aggregating data and converting data from one data type to another. Eg, Transformer, aggregator, sort, Row Merger etc. Passive Stage : A Passive stage handles access to Database for the extraction or writing of data. Eg, IPC stage. File types, Universe, Unidata, DRS stage etc.

57.	What are the types of built in stage?
	These are the following built in stage types : Aggregator : Classifies incoming data into groups, computes totals and other summary functions for each group, and passes them to another stage in the job. This is an active stage. Hashed File : Extracts data from or loads data into databases that contain hashed files. Also acts as an intermediate stage for quick lookups. This is a passive stage. ODBC : Extracts data from or loads data into databases that support the industry standard Open Database Connectivity API. This stage is also used as an intermediate stage for aggregating data. This is a passive stage. Universe : Extracts data from or loads data into UniVerse databases. This stage is also used as an intermediate stage for aggregating data. This is a passive stage.

57.

What are the types of built in stage?

These are the following built in stage types :

Aggregator : Classifies incoming data into groups, computes totals and other summary functions for each group, and passes them to another stage in the job. This is an active stage.
Hashed File : Extracts data from or loads data into databases that contain hashed files. Also acts as an intermediate stage for quick lookups. This is a passive stage.
ODBC : Extracts data from or loads data into databases that support the industry standard Open Database Connectivity API. This stage is also used as an intermediate stage for aggregating data. This is a passive stage.
Universe : Extracts data from or loads data into UniVerse databases. This stage is also used as an intermediate stage for aggregating data. This is a passive stage.

58.	What are Static Hash files and Dynamic Hash files?
	As the names itself suggest what they mean. In general we use Type-30 dynamic Hash files. The Data file has a default size of 2GB and the overflow file is used if the data exceeds the 2GB size.

59.	What are Stage Variables, Derivations and Constants?
	Stage Variable : An intermediate processing variable that retains value during read and doesn’t pass the value into target column. Derivation : Expression that specifies value to be passed on to the target column. Constant : Conditions that are either true or false that specifies flow of data with a link.

60.	What are the types of input links in datastage?
	Stream : A link representing the flow of data. This is the principal type of link, and is used by both active and passive stages. Reference : A link representing a table lookup. Reference links are only used by active stages. They are used to provide information that might affect the way data is changed, but do not supply the data to be changed.

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