Package org.apache.druid.query.aggregation

Class AggregatorFactory

    • Constructor Detail

      • AggregatorFactory

        public AggregatorFactory()

    • Method Detail

      • factorizeVector

        public VectorAggregator factorizeVector​(VectorColumnSelectorFactory selectorFactory)
        Create a VectorAggregator based on the provided column selector factory. Will throw an exception if this aggregation class does not support vectorization: check "canVectorize" first.

      • factorizeWithSize

        public AggregatorAndSize factorizeWithSize​(ColumnSelectorFactory metricFactory)
        Creates an Aggregator based on the provided column selector factory. The returned value is a holder object which contains both the aggregator and its initial size in bytes. The callers can then invoke Aggregator.aggregateWithSize() to perform aggregation and get back the incremental memory required in each aggregate call. Combined with the initial size, this gives the total on-heap memory required by the aggregator.

        This method must include JVM object overheads in the estimated size and must ensure not to underestimate required memory as that might lead to OOM errors.

        This flow does not require invoking guessAggregatorHeapFootprint(long) which tends to over-estimate the required memory.

        Returns:
        AggregatorAndSize which contains the actual aggregator and its initial size.

      • canVectorize

        public boolean canVectorize​(ColumnInspector columnInspector)
        Returns whether or not this aggregation class supports vectorization. The default implementation returns false.

      • getComparator

        public abstract Comparator getComparator()

      • getCombiningFactory

        public abstract AggregatorFactory getCombiningFactory()
        Returns an AggregatorFactory that can be used to combine the output of aggregators from this factory. It is used when we know we have some values that were produced with this aggregator factory, and want to do some additional combining of them. This happens, for example, when merging query results from two different segments, or two different servers. For simple aggregators, the combining factory may be computed by simply creating a new factory that is the same as the current, except with its input column renamed to the same as the output column. For example, this aggregator: {"type": "longSum", "fieldName": "foo", "name": "bar"} Would become: {"type": "longSum", "fieldName": "bar", "name": "bar"} Sometimes, the type or other parameters of the combining aggregator will be different from the original aggregator. For example, the CountAggregatorFactory getCombiningFactory method will return a LongSumAggregatorFactory, because counts are combined by summing. No matter what, `foo.getCombiningFactory()` and `foo.getCombiningFactory().getCombiningFactory()` should return the same result.
        Returns:
        a new Factory that can be used for operations on top of data output from the current factory.

      • getMergingFactory

        public AggregatorFactory getMergingFactory​(AggregatorFactory other)
                                    throws AggregatorFactoryNotMergeableException
        Returns an AggregatorFactory that can be used to combine the output of aggregators from this factory and another factory. It is used when we have some values produced by this aggregator factory, and some values produced by the "other" aggregator factory, and we want to do some additional combining of them. This happens, for example, when compacting two segments together that both have a metric column with the same name. (Even though the name of the column is the same, the aggregator factory used to create it may be different from segment to segment.) This method may throw AggregatorFactoryNotMergeableException, meaning that "this" and "other" are not compatible and values from one cannot sensibly be combined with values from the other.
        Returns:
        a new Factory that can be used for merging the output of aggregators from this factory and other.
        Throws:
        AggregatorFactoryNotMergeableException
        See Also:
        which is equivalent to (when "this" and "other" are the same instance).

      • getRequiredColumns

        @Deprecated
public List<AggregatorFactory> getRequiredColumns()
        Deprecated.
        This was previously used by group-by v1 and will be removed in a future release

      • deserialize

        public abstract Object deserialize​(Object object)
        A method that knows how to "deserialize" the object from whatever form it might have been put into in order to transfer via JSON.
        Parameters:
        object - the object to deserialize
        Returns:
        the deserialized object

      • finalizeComputation

        @Nullable
public abstract Object finalizeComputation​(@Nullable
                                           Object object)
        "Finalizes" the computation of an object. Primarily useful for complex types that have a different mergeable intermediate format than their final resultant output.
        Parameters:
        object - the object to be finalized
        Returns:
        the finalized value that should be returned for the initial query

      • getName

        public abstract String getName()
        Returns:
        output name of the aggregator column.

      • requiredFields

        public abstract List<String> requiredFields()
        Get a list of fields that aggregators built by this factory will need to read.

      • getType

        @Deprecated
public ValueType getType()
        Deprecated.
        This method is deprecated and will be removed soon. Use getIntermediateType() instead. Do not call this method, it will likely produce incorrect results, it exists for backwards compatibility.

      • getFinalizedType

        @Deprecated
public ValueType getFinalizedType()
        Deprecated.
        This method is deprecated and will be removed soon. Use getResultType() instead. Do not call this method, it will likely produce incorrect results, it exists for backwards compatibility.

      • getComplexTypeName

        @Nullable
@Deprecated
public String getComplexTypeName()
        Deprecated.
        This method is deprecated and will be removed soon. Use getIntermediateType() instead. Do not call this method, it will likely produce incorrect results, it exists for backwards compatibility.

      • getMaxIntermediateSize

        public abstract int getMaxIntermediateSize()
        Returns the maximum size that this aggregator will require in bytes for intermediate storage of results.
        Returns:
        the maximum number of bytes that an aggregator of this type will require for intermediate result storage.

      • getMaxIntermediateSizeWithNulls

        public int getMaxIntermediateSizeWithNulls()
        Returns the maximum size that this aggregator will require in bytes for intermediate storage of results. Implementations of AggregatorFactory which need to Support Nullable Aggregations are encouraged to extend NullableNumericAggregatorFactory instead of overriding this method. Default implementation calls makeAggregateCombiner() for backwards compatibility.
        Returns:
        the maximum number of bytes that an aggregator of this type will require for intermediate result storage.

      • withName

        public AggregatorFactory withName​(String newName)
        Used in cases where we want to change the output name of the aggregator to something else. For eg: if we have a query `select a, sum(b) as total group by a from table` the aggregator returned from the native group by query is "a0" set in org.apache.druid.sql.calcite.rel.DruidQuery#computeAggregations. We can use withName("total") to set the output name of the aggregator to "total".

        As all implementations of this interface method may not exist, callers of this method are advised to handle such a case.

        Parameters:
        newName - newName of the output for aggregator factory
        Returns:
        AggregatorFactory with the output name set as the input param.

      • mergeAggregators

        @Nullable
public static AggregatorFactory[] mergeAggregators​(List<AggregatorFactory[]> aggregatorsList)
        Merges the list of AggregatorFactory[] (presumable from metadata of some segments being merged) and returns merged AggregatorFactory[] (for the metadata for merged segment). Null is returned if it is not possible to do the merging for any of the following reason. - one of the element in input list is null i.e. aggregators for one the segments being merged is unknown - AggregatorFactory of same name can not be merged if they are not compatible
        Parameters:
        aggregatorsList -
        Returns:
        merged AggregatorFactory[] or Null if merging is not possible.