Netezza Interview Questions and Answers
by Sachin, on Jul 20, 2022 8:01:33 PM
Q1. What is Netezza?
Netezza is a SQL based platform developed by one of the top companies in the world “IBM” Pvt. Ltd. IBM Netezza is a subsidiary of American technology. This technology offers high-performance data ware appliances and advanced analytical applications. The important functions included are data appliance warehousing, business intelligence, analytic predictions, and business planning. One important thing is that Netezza supports only one data type that is SQL at a time.
Q2. What are the advantages of Netezza?
- Netezza is much easier with hardware and software optimized for data warehousing applications.
- No need for labor intensive tuning
- No requirements needed for partitioning, indexing, and building cubes.
- A Netezza twin fin 12 requires 5 Ip addresses and 4 network droops. The theme of simplicity is reflected in installation as in operations.
Q3. What are the data warehouse appliances?
- Oracle Exadata
Q4. What are the different states of Netezza?
- Online: Normal or usual state.
- Stopped: Netezza will shut down after completing current queries, no new queries allowed.
- Offline: Waits for completion of current queries, new queries in queue receives an error.
- Paused: Same as above, but no error displayed. Typically caused during Netezza boot up or startup.
- Down: Just plain down, could be due to the Netezza server problem or user-initiated.
Q5. What is Netezza used for?
Q6. What is SPU in Netezza?
Q7. What is Netezza architecture?
The Netezza architecture combines the best elements of Symmetric Multiprocessing (SMP) and Massively Parallel Processing (MPP) to create an appliance purpose-built for analyzing petabytes of data quickly.
Q8. What is a Netezza appliance?
Q9. What is Spa in Netezza?
Q10. What is snippet in Netezza?
Q11. What are zone maps?
An extent is the smallest unit of disk allocation on an SPU. Zone maps are internal mapping structures to the extent that take advantage of the internal ordering of data to eliminate extents that do not need to be scanned. Zone maps transparently avoid scanning of unreferenced rows. Zone maps are created for every column in the table and contain the minimum and maximum values for every extent.
Q12. What is the difference between generate statistics and generate express statistics?
- Generate statistics is used to gather statistics about each table column’s proportion of duplicate values, minimum values, maximum values, null values, unique values, and updates the system catalog tables.
- The difference between ‘generate statistics’ and ‘generate express statistics’ is based on how the column uniqueness is calculated. The ‘generate express statistics’ calculates estimated dispersion values based on the sampling of rows in the table. ‘Generate express statistics’ uses approximation in generating the stats whereas ‘generate statistics’ uses all the rows in the table.
Q13. What are the partitioning methods available in Netezza?
- Random partitioning: Distributes the data randomly.
- Hash Partitioning: Distributes the data on the specified columns.
Q14. What is collocated join?
When you join tables that are distributed on the same key and used these key columns in the join condition, then each SPU in Netezza works 100% independent of the other, as the required data is available in itself. This type of joins is called collocated joins.
Q15. What is nzload?
Nzload utility is used to load data from a file into a table. It is used to load bulk data quickly and simultaneously rejects erroneous content.
Q16. What is the use of creating materialized views?
A materialized view reduces the width (number of columns) of data being scanned in the base table by creating a thin version (fewer columns) of the base table that contains a small subset of frequently queried columns.
Q17. What are the best practices of creating materialized views?
- Create materialized views with few columns which are frequently queried.
- Specify order by clause on the most restrictive columns (columns used in where clause).
- Periodically or manually refresh the materialized views.
Q18. What are the limitations of materialized views?
- You cannot insert, update, delete, or truncate a materialized view. Any changes on the base tables will reflect materialized views.
- You can specify only one base table in the from clause.
- The base table can’t be an external table, a system table, or a temporary table.
- You cannot use a where clause in the materialized view.
- Expressions are not allowed as columns.
Q19. What are the join types in Netezza?
- Hash join
- Merge Sort join
- Expression join
- Exist join
- Cross Product Join
Q20. What are the data loading formats supported by Netezza?
Netezza supports 3 data loading formats for loading the data from external sources.
- Text-delimited - every row or record should end with a delimiter.
- Fixed-length - allows an expressive form of the external table definition.
- Compressed binary - compresses the data before a backup or restore.
Q21. What are the different ways to load data?
- The nzload command
- External tables
- Create table AS
- The nz_migrate utility