ETL Tools Lookup Stage

By using the Lookup stage we will combine the data from multiple table. By using join stage also we will combine the data from multiple tables. Then what is the need of Lookup stage?

Questions by nagarjuna900   answers by nagarjuna900

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Lookup, Joiner and Merger these 3 stages use for joining the data. Where these 3 stages vary
is during capturing of unmatched data and performance.

Joiner: If you joiner you can not
capture unmatched data but joiner provides good performance because it supports sorted data inputs compare to lookup stage.
Lookup:
If you lookup stage you can capture unmatched master data.
Merge: If you use merger you can capture N no. of unmatched reference data sets.

Join and lookup is differ in terms of memory usage. Join is light weight than lookup stage. Join stage won't use much system resources. While performing lookup will used more system resources. In case of lookup it fetch the whole data from refernce link into RAM memory and then it perform lookup.

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There are three things to consider here
1.memory usage

  As with joiner fewer rows has to be in memory at any time.This is not with lookup

2.treating of rows with unmatched keys
 
  Joiner will send the null value if the row is unmatched but look-up will reject the row.

3.their requirements for data being input  for example sorting of rows


hope this will clear your doubt

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