Creates a copy of an existing contiguous map. The copy uses dedicated fallback.
- The name of the existing contiguous map to copy. The existing map must use legacy fallback.
When a table has FALLBACK protection, Teradata Database stores two copies of every row in the table, a primary copy and a fallback copy. The fallback copy is stored on a different AMP than the primary copy. This protects against failure of the AMP storing the primary copy. AMPs are assigned to clusters, in which the AMPs provide fallback protection for each other. A cluster must consist of at least two AMPs and is limited to at most eight AMPs.
Dedicated fallback was introduced with the Teradata Database MAPS Architecture feature in Teradata Database 16.10. In this scheme, one AMP in the cluster stores all fallback rows for one other AMP in the cluster. For example, consider a four-AMP cluster (AMPs 0, 1, 2, and 3). If AMP 0 has nine rows, AMP 1 has all nine fallback rows for AMP 0; AMPs 2 and 3 do not have any fallback rows for AMP 0. Similarly, AMP 2 provides fallback protection for AMP 1, AMP 3 for AMP 2, and AMP 0 for AMP 3.
- Legacy fallback was used in versions of Teradata Database prior to 16.10. In this scheme, each AMP in a cluster contains fallback copies of primary data from all the other AMPs in the cluster. For example, consider a four-AMP cluster (AMPs 0, 1, 2, and 3). If AMP 0 contains nine rows of primary data, the fallback copies of those rows are spread among AMPs 1, 2, and 3.
Example: Duplicating a map
The following contiguous maps are defined on this system: TD_GlobalMap (Map Number 1) has Amps 0-7 and 2 PEs defined. TD_DataDictionaryMap (Map Number 2) has Amps 0-7 and 2 PEs defined. TD_Map1 (Map Number 1025) has Amps 0-7 and 2 PEs defined (System Default Map). > dup map td_map1 Map TD_Map2 is created.