จะใช้ Lookup Stage หรือ Join Stage ดี

The two major ways of combining data in a WebSphere DataStage job are via a Lookup stage or a Join stage. 

How do you decide which one to use? Lookup and Join stages perform equivalent operations: combining two or more input data sets based on one or more specified keys. 

1. คำนึงถึงปริมาณข้อมูลและการ Sort ของ Input Link

When one unsorted input is very large or sorting is not feasible, Lookup is preferred. 

When all inputs are of manageable size or are pre-sorted, Join is the preferred solution.

2. คำนึงถึงปริมาณข้อมูลของ Reference Data

The Lookup stage is most appropriate when the reference data for all Lookup stages in a job is small enough to fit into available physical memory. 

If performance issues arise while using Lookup, consider using the Join stage. The Join stage must be used if the data sets are larger than available memory resources.

3. คำนึงถึงปริมาณข้อมูลของ Input เมื่อเปรียบเทียบกับ Reference Data

If the reference to a lookup is directly from a DB2® or Oracle table and the number of input rows is significantly smaller than the reference rows, 1:100 or more, a Sparse Lookup might be appropriate.