Explain the concept of persistent cache and dynamic cache in Lookup transformation.

Persistent Cache vs. Dynamic Cache in Lookup Transformation

In Informatica PowerCenter, the Lookup Transformation can use different caching mechanisms to improve performance. Two important caching types are Persistent Cache and Dynamic Cache.

1. Persistent Cache

Definition :

A persistent cache retains lookup data across multiple session runs, avoiding the need to rebuild the cache every time a workflow runs. This is useful when the lookup table does not change frequently.

How It Works :

The cache is created during the first session execution and stored on disk.
In subsequent runs, the session reuses the same cache, reducing database queries.
Used in scenarios where lookup data remains mostly static.

Use Case Example :

* A product price list lookup that rarely changes can use a persistent cache to avoid querying the database repeatedly.

2. Dynamic Cache

Definition :

A dynamic cache updates itself during session execution. When new data is found in the source, it is added to the cache, and future lookups can use this updated data without querying the database.

How It Works :

The lookup table and cache are updated when a new value is found.
Used mainly for slowly changing dimensions (SCD Type 1).
Helps avoid duplicate records by checking if a record exists before inserting it.

Use Case Example :

* In a customer dimension table, if a new customer is found, their details are added to the dynamic cache and later used for future lookups without additional database queries.

Key Differences Between Persistent Cache and Dynamic Cache

Feature	Persistent Cache	Dynamic Cache
Purpose	Reuses cached data across multiple runs.	Updates cache during session execution.
Data Modification	Data remains unchanged between runs.	New lookup entries are added during the session.
Use Case	Static reference data (e.g., country codes, price lists).	Slowly changing dimensions (SCD Type 1) or avoiding duplicate inserts.
Performance	Faster for repetitive lookups across sessions.	Helps avoid redundant database calls during a session.