5.4 Parallel Queries

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In an ideal world parallel queries are useful on multiple CPU platforms when Oracle Partitioning is being used with separate disks or RAID arrays. Generally parallel queries are only an advantage for very large tables or in very large databases such as data warehouses.

Using parallel queries on small highly active concurrent OLTP databases can cause rather than solve performance problems. There will be more on parallel queries and Oracle Partitioning in Chapter 17. Certain types of SQL can be executed in parallel.

• Any query with at least a single table scan using SELECT, INSERT, UPDATE, and DELETE commands.

• The CREATE INDEX and ALTER INDEX REBUILD commands.

• Using the CREATE TABLE command generating a table from a SELECT command.

• Partitions with local indexes where a local index is an index created on each separate partition.

That is the basics of Oracle SQL DML Data Manipulation Language. In the next chapter we will start to examine the concepts of creating efficient SQL code.

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