What do you mean by data warehouse? Explain the query manager.

Data Warehouse :

In computing, a data warehouse (DWDWH), or an enterprise data warehouse (EDW), is a system used for reporting and data analysis. Integrating data from one or more disparate sources creates a central repository of data, a data warehouse (DW). Data warehouses store current and historical data and are used for creating trending reports for senior management reporting such as annual and quarterly comparisons.

The data stored in the warehouse is uploaded from the operational systems (such as marketing, sales, etc., shown in the figure to the right). The data may pass through an operational data store for additional operations before it is used in the DW for reporting.

A data warehouse maintains a copy of information from the source transaction systems. This architectural complexity provides the opportunity to :

  • Congregate data from multiple sources into a single database so a single query engine can be used to present data.
  • Mitigate the problem of database isolation level lock contention in transaction processing systems caused by attempts to run large, long running, analysis queries in transaction processing databases.
  • Maintain data history, even if the source transaction systems do not.
  • Integrate data from multiple source systems, enabling a central view across the enterprise. This benefit is always valuable, but particularly so when the organization has grown by merger.
  • Improve data quality, by providing consistent codes and descriptions, flagging or even fixing bad data.
  • Present the organization’s information consistently.
  • Provide a single common data model for all data of interest regardless of the data’s source.
  • Restructure the data so that it makes sense to the business users.
  • Restructure the data so that it delivers excellent query performance, even for complex analytic queries, without impacting the operational systems.
  • Add value to operational business applications, notably customer relationship management (CRM) systems.
  • Making decision–support queries easier to write.

Query Manager : 

The query manager the system component that performs all the operations necessary to support the query management process. The system is typically constructed using a combination of user access tasks, data warehousing monitor tools , native database facilities and shell script.

The architecture of query manager perform following operations :

– Direct queries to the appropriate table

– Schedule the execution of the user queries

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