Amazon Redshift interview questions

26. What happens if a table in my local storage has the same name as an external table?
Just like with local tables, you can use the schema name to pick exactly which one you mean by using schema_name.table_name in your query.

27. Whether redshift is a columnar storage database ?
Redshift is a columnar storage database, which is optimized for huge and repetitive type of data. Using columnar storage, reduces the I/O operations on disk drastically, improving performance as a result. Redshift gives you an option to define column-based encoding for data compression. Columnar data stores can be compressed much more than row-based data stores because similar data is stored sequentially on disk.

28. Is Redshift Massively Parallel Processing ? What is it all about ?
Amazon Redshift automatically distributes data and query load across all nodes. Amazon Redshift makes it easy to add nodes to your data warehouse and enables you to maintain fast query performance as your data warehouse grows.

29. Will Amazon Redshift back up my data? How do I restore my cluster from a backup?
Amazon Redshift replicates all your data within your data warehouse cluster when it is loaded and also continuously backs up your data to S3. Amazon Redshift always attempts to maintain at least three copies of your data (the original and replica on the compute nodes and a backup in Amazon S3). Redshift can also asynchronously replicate your snapshots to S3 in another region for disaster recovery.

30. Can you give the list of System catalog tables ?
Querying the catalog tables

31. What happens to my backups if I delete data warehouse cluster?
When you delete a data warehouse cluster you have the ability to specify whether a final snapshot is created upon deletion. This enables a restore of the deleted data warehouse cluster at a later date. All previously created manual snapshots of your data warehouse cluster will be retained and billed at standard Amazon S3 rates, unless you choose to delete them.

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