Parallel hint in TERADATA

In Teradata, the PARALLEL hint is used to instruct the optimizer to consider parallel execution plans for SQL queries. Teradata is a massively parallel processing (MPP) database system designed to distribute query processing across multiple nodes, providing scalability and high-performance parallelism.

Here's an example of how to use the PARALLEL hint in Teradata:

SELECT /*+PARALLEL(4)*/ * FROM TableName;

In this example:

- /*+PARALLEL(4)*/ is the hint that instructs the Teradata optimizer to consider parallel execution with a degree of parallelism of 4 for the specified query. You can adjust the number (4 in this case) based on your system resources and query requirements.

- TableName is the name of the table from which you want to retrieve data.

It's important to note the following points when using the PARALLEL hint in Teradata:

1. Parallel execution in Teradata is most effective for large queries involving significant amounts of data that can benefit from parallel processing across multiple nodes.

2. The degree of parallelism specified should not exceed the available system resources, such as the number of AMPs (Access Module Processors) and available CPU cores.

3. Teradata's optimizer evaluates the query and determines whether parallel execution is suitable based on factors such as query complexity, data distribution, and available resources.

4. You should carefully analyze the performance impact of parallel execution on your specific workload and tune the degree of parallelism accordingly.

Additionally, Teradata provides other options and features for controlling parallelism and optimizing query performance, such as workload management (WLM) settings, indexing strategies, and partitioning techniques. It's essential to consider these factors comprehensively when optimizing query performance in Teradata.