What is fallback option in Teradata?
Fallback. Fallback protects the table data by storing the second copy of rows of a table on another AMP called as Fallback AMP. If one AMP fails, then the fallback rows are accessed. With this, even if one AMP fails, data is still available through fallback AMP.
What are the features of Teradata?
Features of Teradata
- 1) Linear Scalability.
- 2) Unlimited Parallelism.
- 3) Mature Optimizer.
- 4) Shared Nothing Architecture.
- 5) Connectivity.
- 6) Low TCO.
- 7) SQL.
- 8) Load & Unload utilities.
What is Mergeblockratio in Teradata?
The MERGEBLOCKRATIO option provides a way to combine existing small data blocks into a single larger data block during full table modification operations for permanent tables and permanent journal tables. This option is not available for volatile and global temporary tables.
What is before journal and after journal in Teradata?
The permanent journal in Teradata provides the capability to capture the snapshot of the table/tables before and after applying changes using DML statements like insert, delete and update.
What is fallback and Journal in Teradata?
Journals are used for recovery purpose bascially as for Rollback(before) or rollforward(after) in case in software or hardware failure. fallback is nothing but copy of table which reside on different AMP .
What is the fallback or no fallback option while creating table DDL?
During table creation or after a table is created, you may specify whether or not the system should keep a Fallback copy of the table. If Fallback is specified, it is automatic and transparent. Fallback guarantees that the two copies of a row will always be on different AMPs.
What is main feature of the Teradata database?
With linear scalability (Software can scale linearly with hardware), unconditional parallelism, multi-faceted parallelism, intelligent data distribution, parallel-aware optimizer makes Teradata is capable of handling large data and complex queries.
Which feature is unique to Teradata?
Teradata is a broadly used relational database management system (RDBMS), that can be identified for its special capabilities on being consistent data and transactions, extensive security features, outstanding in parallelism, upright in performance, strong and robust structure, higher convenience for scalability.
What is checksum in Teradata?
For more on Teradata CHECKSUM see documentation. As for the CHECKSUM purpose, it’s an additional (to file system) data integrity verification. The hash is calculated over data being written, and is written alongside it. On subsequent read hash is calculated from read data, and compared.
What is map in Teradata DDL?
Under Teradata Database MAPS Architecture, every table uses a map that specifies which AMPs store the rows of the table. The map associates each AMP with a set of hash values. For tables with fallback, the primary and fallback copies of the row are stored on different AMPs in the map.
What does no fallback mean in Teradata?
Fallback is a Teradata Database feature that protects data in the case of an AMP vproc failure. Fallback protects your data by storing a second copy of each row of a table on a different AMP in the same cluster. If an AMP fails, the system accesses the Fallback rows to meet requests.
What is confidence level in Teradata?
Low Confidence – Statistics are existing on the index but AND/OR condition are there in the query. No confidence – Statistics not found in the step, finds AND condition on non-index columns. Join Index confidence – Unique index is used or foreign key relationship between the two tables.