INTERVIEW QUESTIONS DATA WAREHOUSING INFORMATICA DETAILS

Question: When do u use a unconnected lookup and connected lookup....

what is the difference between dynamic and static lookup...y and when do v use these types of lookups ( ie...dynamic and static )

Answer: In static lookup cache, you cache all the lookup data at the starting of the session. in dynamic lookup cache, you go and query the database to get the lookup value for each record which needs the lookup. static lookup cache adds to the session run time....but it saves time as informatica does not need to connect to your databse every time it needs to lookup. depending on how many rows in your mapping needs a lookup, you can decide on this...also remember that static lookup eats up space...so remember to select only those columns which are needed

In static lookup cache, you cache all the lookup data at the starting of the session. in dynamic lookup cache, you go and query the database to get the lookup value for each record which needs the lookup. static lookup cache adds to the session run time....but it saves time as informatica does not need to connect to your databse every time it needs to lookup. depending on how many rows in your mapping needs a lookup, you can decide on this...also remember that static lookup eats up space...so remember to select only those columns which are needed Source: CoolInterview.com

Unconnected Lookup
Physically unconnected from other transformations-NO data flow
arrows leading to or from an unconnected Lookup
Lookup data is called from the point in the Mapping that needs it so there are less number of looks up
Lookup function can be set within any transformation that supports
expressions. Source: CoolInterview.com

Unconnected lookup will be used if we need to use same lookup tx multiple times within the same mapping.
Connected lookup will be used if we need to use a lookup Tx only once in a mapping.
Differance B/w Dynamic and static lookup:
1.if we use Dynamic lookup, the Integration service wll query the lookup source once and builds a cache which can be inserted/updated based on the availability of new records and the changes in the source records before loading to target table.
If we use static lookup, the cache will be build by the integration service when the a row from the source requests lookup first time. Integration Service doesn't inserts/updates the lookup cache based on the new rows/changes from the source
2.Static lookup could be both connected and unconnected whereas Dynamic lookup will be only connected.
3.static lookup will not consume much memory when compared to Dynamic lookup.

Dynamic lookup wll be used if there is a chance of getting a new record and a change in that record as 2 differant rows in a single session run.
Ex: row1:creation of a Customer c1 data; Row2: Changing the profile of the same customer c1. Here , row 1 should be inserted to target and row2 should be updated to target.
Static lookup will be used if there is no chance to get above case. Source: CoolInterview.com

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