Package org.apache.druid.segment.column

Interface ColumnIndexSupplier

All Known Implementing Classes:

ExpressionPredicateIndexSupplier, NestedDataColumnSupplier, NestedFieldColumnIndexSupplier, NoIndexesColumnIndexSupplier, NullValueIndexSupplier, ScalarDoubleColumnAndIndexSupplier, ScalarLongColumnAndIndexSupplier, ScalarStringColumnAndIndexSupplier, StringUtf8ColumnIndexSupplier, VariantColumnAndIndexSupplier

public interface ColumnIndexSupplier

Provides indexes and information about them (ColumnIndexCapabilities) for a column. Indexes which satisfy the Filter used in a Query, allow the query engine to construct Offset (and VectorOffset) to build Cursor (and VectorCursor). This allows the engine to only scan the rows which match the filter values, instead of performing a full scan of the column and using a ValueMatcher (or VectorValueMatcher) to filter the values.

Method Summary

Modifier and Type	Method	Description
<T> T	as(Class<T> clazz)	Try to get a column 'index' of the specified type.

Method Details

as

@Nullable
<T> T as(Class<T> clazz)

Try to get a column 'index' of the specified type. If the index of the desired type is not available, this method will return null. If the value is non-null, the index may be used for the eventual construction of an Offset to form the basis of a Cursor (or VectorOffset and VectorCursor) which can greatly reduce the total number of rows which need to be scanned and processed. Objects returned by this method are not thread-safe. There are several built-in index classes which can be passed as an argument to this method when used from Filter.getBitmapColumnIndex(ColumnIndexSelector). Implementors of this interface should provide as many of them as possible to participate fully in as many Filter as possible, as different filters require different index types, and may prefer some over others. Indexes for matching a row to a specific value:

See Also:

• NullValueIndex
• Indexes for matching a row to any of a set of values:
• ValueSetIndexes
• Indexes for matching a row to a range of values:
• LexicographicalRangeIndexes
• Indexes for matching an array element of a row to a specific value:
• Indexes for matching a row using a org.apache.druid.query.filter.DruidPredicateFactory:
• Speciality indexes:
• Low level access to implementation specific index stuff not particularly suitable for use in filtering:
• DictionaryEncodedValueIndex
• DictionaryEncodedStringValueIndex