What is USI and nusi in Teradata?
The main difference between the USI and NUSI is that USI subtable rows are hashed and the NUSI subtable rows are AMP-Local. Each row of the subtable only tracks the base rows on the same AMP. This is what is meant by AMP Local.
What is nusi in Teradata?
The Teradata Non-Unique Secondary Index (NUSI) is an alternative data access path that can reduce IOs. Base table rows are hashed by the primary index column values, while the nonunique secondary index rows are co-located with their base table rows on the same AMP: NUSI rows are not hash distributed.
How do I create a value ordered secondary index in Teradata?
CREATE UNIQUE INDEX [index_name](col1,col2) ON [databasename. table_name]; ➠ Non-Unique Secondary Index (NUSI): It means that the values for the selected column can have duplicates. NUSI sub-tables are local to the AMP corresponding to its base table and by default, are sorted in row hash of the secondary index column.
How many secondary Indexs are there in Teradata?
32 Secondary Indexes
Non-Unique Secondary Index (NUSI) When A NUSI is created, then the Teradata will immediately build a secondary index subtable on each AMP. Each AMP will hold the secondary index values for their rows in the base table only. There can be up to 32 Secondary Indexes on a table.
What is PPI in Teradata?
Partitioned Primary Index (PPI) is an indexing mechanism that is useful in improving the performance of certain queries. When rows are inserted into a table, they are stored in an AMP and arranged by their row hash order. Rows are assigned to a partition based on the partition expression defined.
What is full table scan in Teradata?
A full-table scan is a retrieval mechanism that touches all rows in a table. Teradata Database always uses a full-table scan to access the data of a table if a query: Accesses a NoPI table that does not have an index defined on it.
What is the difference between primary and secondary index in Teradata?
Difference Between Primary Index and Secondary Index A primary index is an index on a set of fields that includes the unique primary key and is guaranteed not to contain duplicates. In contrast, a secondary index is an index that is not a primary index and may have duplicates.
Where is PPI table in Teradata?
To identify PPI columns in Teradata
- Select databasename, tablename, columnposition, columnname.
- from dbc. indices.
- where indextype =’Q’
- order by 1 ,2,3 ;
What is Vdisk in Teradata?
Teradata offers a set of Virtual Disks for each AMP. The storage area of each AMP is called as Virtual Disk or Vdisk. The steps for executing the query are below: The user fires the query which is sent to PE. PE returns back the data to the user.
What is NuSI in Teradata?
NUSI – The Nonunique Secondary Index in Teradata. The Technical Details of the Non-Unique Secondary Index in Teradata – NUSI. Many concepts of Teradata indexing are tightly coupled to the physical storage of data rows. The Teradata Non-Unique Secondary Index (NUSI) is an alternative data access path which can help to reduce IOs.
What is the non-unique secondary index in Teradata?
The Technical Details of the Non-Unique Secondary Index in Teradata – NUSI. Many concepts of Teradata indexing are tightly coupled to the physical storage of data rows. The Teradata Non-Unique Secondary Index (NUSI) is an alternative data access path which can help to reduce IOs.
How do I retrieve a range of dates in Teradata?
If you need to retrieve a range of dates, a value ordered NUSI on the data column makes sense (dates can be utilized, as Teradata stores them as 4-byte integer values). Before the availability of join indexes and partitioning, this was the only method to access ranges of dates in an optimized way.
When should you create a subtable in Teradata?
As soon as you define secondary index, the next move comes from Teradata creating a Subtable on every AMP. This is true for both the USI and the NUSI. Subtables require additional disk space and maintenance; they should be only used on queries that run again and again.