org.apache.druid.segment.column

Interface ColumnCapabilities

All Known Implementing Classes:

ColumnCapabilitiesImpl

public interface ColumnCapabilities

This interface is used to expose information about columns that is interesting to know for all matters dealing with reading from columns, including query planning and optimization, creating readers to merge segments at ingestion time, and probably nearly anything else you can imagine.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	ColumnCapabilities.Capable
static interface	ColumnCapabilities.CoercionLogic This interface define the shape of a mechnism to allow for bespoke coercion of ColumnCapabilities.Capable.UNKNOWN into ColumnCapabilities.Capable.TRUE or ColumnCapabilities.Capable.FALSE for each ColumnCapabilities.Capable of a ColumnCapabilities, as is appropriate for the situation of the caller.

Method Summary

Modifier and Type	Method and Description
ColumnCapabilities.Capable	areDictionaryValuesSorted() If the column is dictionary encoded, are those values sorted? Useful to know for optimizations that can defer looking up values and allowing sorting with the dictionary ids directly
ColumnCapabilities.Capable	areDictionaryValuesUnique() If the column is dictionary encoded, is there a 1:1 mapping of dictionary ids to values? If this is true, it unlocks optimizations such as allowing for things like grouping directly on dictionary ids and deferred value lookup
String	getComplexTypeName() If ValueType is COMPLEX, then the typeName associated with it.
ValueType	getType() Column type, good to know so caller can know what to expect and which optimal selector to use
boolean	hasBitmapIndexes() Does the column have an inverted index bitmap for each value? If so, these may be employed to 'pre-filter' the column by examining if the values match the filter and intersecting the bitmaps, to avoid having to scan and evaluate if every row matches the filter
ColumnCapabilities.Capable	hasMultipleValues() String columns are sneaky, and might have multiple values, this is to allow callers to know and appropriately prepare themselves
ColumnCapabilities.Capable	hasNulls() Does this column contain null values? If so, callers, especially for primitive numeric columns, will need to check for null value rows and act accordingly
boolean	hasSpatialIndexes() Does the column have spatial indexes available to allow use with spatial filtering?
ColumnCapabilities.Capable	isDictionaryEncoded() Is the column dictionary encoded? If so, a DimensionDictionarySelector may be used instead of using a value selector, allowing algorithms to operate on primitive integer dictionary ids rather than the looked up dictionary values
boolean	isFilterable() All Druid primitive columns support filtering, maybe with or without indexes, but by default complex columns do not support direct filtering, unless provided by through a custom implementation.

Method Detail

getType

ValueType getType()

Column type, good to know so caller can know what to expect and which optimal selector to use

getComplexTypeName

@Nullable
String getComplexTypeName()

If ValueType is COMPLEX, then the typeName associated with it.

isDictionaryEncoded

ColumnCapabilities.Capable isDictionaryEncoded()

Is the column dictionary encoded? If so, a DimensionDictionarySelector may be used instead of using a value selector, allowing algorithms to operate on primitive integer dictionary ids rather than the looked up dictionary values

areDictionaryValuesSorted

ColumnCapabilities.Capable areDictionaryValuesSorted()

If the column is dictionary encoded, are those values sorted? Useful to know for optimizations that can defer looking up values and allowing sorting with the dictionary ids directly

areDictionaryValuesUnique

ColumnCapabilities.Capable areDictionaryValuesUnique()

If the column is dictionary encoded, is there a 1:1 mapping of dictionary ids to values? If this is true, it unlocks optimizations such as allowing for things like grouping directly on dictionary ids and deferred value lookup

hasMultipleValues

ColumnCapabilities.Capable hasMultipleValues()

String columns are sneaky, and might have multiple values, this is to allow callers to know and appropriately prepare themselves

hasBitmapIndexes

boolean hasBitmapIndexes()

Does the column have an inverted index bitmap for each value? If so, these may be employed to 'pre-filter' the column by examining if the values match the filter and intersecting the bitmaps, to avoid having to scan and evaluate if every row matches the filter

hasSpatialIndexes

boolean hasSpatialIndexes()

Does the column have spatial indexes available to allow use with spatial filtering?

isFilterable

boolean isFilterable()

All Druid primitive columns support filtering, maybe with or without indexes, but by default complex columns do not support direct filtering, unless provided by through a custom implementation.

hasNulls

ColumnCapabilities.Capable hasNulls()

Does this column contain null values? If so, callers, especially for primitive numeric columns, will need to check for null value rows and act accordingly