An attribute-clustered table is a heap-organized table that stores data in close proximity on disk based on user-specified clustering directives. The directives specify columns in single or multiple tables.
The directives are as follows:
- The
CLUSTERING ... BY LINEAR ORDERdirective orders data in a table according to specified columns.Consider usingBY LINEAR ORDERclustering, which is the default, when queries qualify the prefix of columns specified in the clustering clause. For example, if queries ofsh.salesoften specify either a customer ID or both customer ID and product ID, then you could cluster data in the table using the linear column ordercust_id,prod_id.
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CLUSTERING ... BY INTERLEAVED ORDERdirective orders data in one or more tables using a special algorithm, similar to a Z-order function, that permits multicolumn I/O reduction.Consider usingBY INTERLEAVED ORDERclustering when queries specify a variety of column combinations. For example, if queries ofsh.salesspecify different dimensions in different orders, then you can cluster data in thesalestable according to columns in these dimensions.
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Attribute clustering is only available for direct path INSERT operations. It is ignored for conventional DML.
This section contains the following topics:
- Advantages of Attribute-Clustered Tables
- Join Attribute Clustered Tables
- I/O Reduction Using Zones
- Attribute-Clustered Tables with Linear Ordering
- Attribute-Clustered Tables with Interleaved Ordering
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