Package org.apache.druid.segment

Interface DimensionIndexer<EncodedType extends Comparable<EncodedType>,​EncodedKeyComponentType,​ActualType extends Comparable<ActualType>>

  • Type Parameters:
    EncodedType - class of a single encoded value
    EncodedKeyComponentType - A row key contains a component for each dimension, this param specifies the class of this dimension's key component. A column type that supports multivalue rows should use an array type (e.g., Strings would use int[]). Column types without multivalue row support should use single objects (e.g., Long, Float).
    ActualType - class of a single actual value
    All Known Implementing Classes:
    AutoTypeColumnIndexer, DictionaryEncodedColumnIndexer, DoubleDimensionIndexer, FloatDimensionIndexer, LongDimensionIndexer, NestedDataColumnIndexerV4, StringDimensionIndexer
    public interface DimensionIndexer<EncodedType extends Comparable<EncodedType>,​EncodedKeyComponentType,​ActualType extends Comparable<ActualType>>
    Processing related interface A DimensionIndexer is a per-dimension stateful object that encapsulates type-specific operations and data structures used during the in-memory ingestion process (i.e., work done by IncrementalIndex). Ingested row values are passed to a DimensionIndexer, which will update its internal data structures such as a value->ID dictionary as row values are seen. The DimensionIndexer is also responsible for implementing various value lookup operations, such as conversion between an encoded value and its full representation. It maintains knowledge of the mappings between encoded values and actual values. Sorting and Ordering -------------------- When encoding is present, there are two relevant orderings for the encoded values. 1.) Ordering based on encoded value's order of ingestion 2.) Ordering based on converted actual value Suppose we have a new String dimension DimA, which sees the values "Hello", "World", and "Apple", in that order. This would correspond to dictionary encodings of "Hello"=0, "World"=1, and "Apple"=2, by the order in which these values were first seen during ingestion. However, some use cases require the encodings to be sorted by their associated actual values. In this example, that ordering would be "Apple"=0, "Hello"=1, "World"=2. The first ordering will be referred to as "Unsorted" in the documentation for this interface, and the second ordering will be referred to as "Sorted". The unsorted ordering is used during ingestion, within the IncrementalIndexRow keys; the encodings are built as rows are ingested, taking the order in which new dimension values are seen. The generation of a sorted encoding takes place during segment creation when indexes are merged/persisted. The sorted ordering will be used for dimension value arrays in that context and when reading from persisted segments. Note that after calling the methods below that deal with sorted encodings, - getUnsortedEncodedValueFromSorted() - getSortedIndexedValues() - convertUnsortedEncodedKeyComponentToSortedEncodedKeyComponent() calling processRowValsToUnsortedEncodedKeyComponent() afterwards can invalidate previously read sorted encoding values (i.e., new values could be added that are inserted between existing values in the ordering). Thread Safety -------------------- Each DimensionIndexer exists within the context of a single IncrementalIndex. Before IndexMerger.persist() is called on an IncrementalIndex, any associated DimensionIndexers should allow multiple threads to add data to the indexer via processRowValsToUnsortedEncodedKeyComponent() and allow multiple threads to read data via methods that only deal with unsorted encodings. As mentioned in the "Sorting and Ordering" section, writes and calls to the sorted encoding methods should not be interleaved: the sorted encoding methods should only be called when it is known that writes to the indexer will no longer occur. The implementations of methods dealing with sorted encodings are free to assume that they will be called by only one thread. The sorted encoding methods are not currently used outside of index merging/persisting (single-threaded context, and no new events will be added to the indexer). If an indexer is passed to a thread that will use the sorted encoding methods, the caller is responsible for ensuring that previous writes to the indexer are visible to the thread that uses the sorted encoding space. For example, in the RealtimePlumber and IndexGeneratorJob, the thread that performs index persist is started by the same thread that handles the row adds on an index, ensuring the adds are visible to the persist thread.

    • Method Detail

      • processRowValsToUnsortedEncodedKeyComponent

        EncodedKeyComponent<EncodedKeyComponentType> processRowValsToUnsortedEncodedKeyComponent​(@Nullable
                                                                                         Object dimValues,
                                                                                         boolean reportParseExceptions)
        Encodes the given row value(s) of the dimension to be used within a row key. It also updates the internal state of the DimensionIndexer, e.g. the dimLookup.

        For example, the dictionary-encoded String-type column will return an int[] containing dictionary IDs.

        Parameters:
        dimValues - Value(s) of the dimension in a row. This can either be a single value or a list of values (for multi-valued dimensions)
        reportParseExceptions - true if parse exceptions should be reported, false otherwise
        Returns:
        Encoded dimension value(s) to be used as a component for the row key. Contains an object of the DimensionIndexer and the effective size of the key component in bytes.

      • setSparseIndexed

        void setSparseIndexed()
        This method will be called while building an IncrementalIndex whenever a known dimension column (either through an explicit schema on the ingestion spec, or auto-discovered while processing rows) is absent in any row that is processed, to allow an indexer to account for any missing rows if necessary. Useful so that a string DimensionSelector built on top of an IncrementalIndex may accurately report DimensionDictionarySelector.nameLookupPossibleInAdvance() by allowing it to track if it has any implicit null valued rows. At index persist/merge time all missing columns for a row will be explicitly replaced with the value appropriate null or default value.

      • getUnsortedEncodedValueFromSorted

        EncodedType getUnsortedEncodedValueFromSorted​(EncodedType sortedIntermediateValue)
        Given an encoded value that was ordered by associated actual value, return the equivalent encoded value ordered by time of ingestion. Using the example in the class description: getUnsortedEncodedValueFromSorted(2) would return 0
        Parameters:
        sortedIntermediateValue - value to convert
        Returns:
        converted value

      • getSortedIndexedValues

        CloseableIndexed<ActualType> getSortedIndexedValues()
        Returns an indexed structure of this dimension's sorted actual values. The integer IDs represent the ordering of the sorted values. Using the example in the class description: "Apple"=0, "Hello"=1, "World"=2
        Returns:
        Sorted index of actual values

      • getMinValue

        ActualType getMinValue()
        Get the minimum dimension value seen by this indexer. NOTE: On an in-memory segment (IncrementalIndex), we can determine min/max values by looking at the stream of row values seen in calls to processSingleRowValToIndexKey(). However, on a disk-backed segment (QueryableIndex), the numeric dimensions do not currently have any supporting index structures that can be used to efficiently determine min/max values. When numeric dimension support is added, the segment format should be changed to store min/max values, to avoid performing a full-column scan to determine these values for numeric dims.
        Returns:
        min value

      • getMaxValue

        ActualType getMaxValue()
        Get the maximum dimension value seen by this indexer.
        Returns:
        max value

      • getCardinality

        int getCardinality()
        Get the cardinality of this dimension's values.
        Returns:
        value cardinality

      • makeDimensionSelector

        DimensionSelector makeDimensionSelector​(DimensionSpec spec,
                                        IncrementalIndexRowHolder currEntry,
                                        IncrementalIndex.DimensionDesc desc)
        Return an object used to read values from this indexer's column as Strings.
        Parameters:
        spec - Specifies the output name of a dimension and any extraction functions to be applied.
        currEntry - Provides access to the current Row object in the Cursor
        desc - Descriptor object for this dimension within an IncrementalIndex
        Returns:
        A new object that reads rows from currEntry

      • makeColumnValueSelector

        ColumnValueSelector<?> makeColumnValueSelector​(IncrementalIndexRowHolder currEntry,
                                               IncrementalIndex.DimensionDesc desc)
        Return an object used to read values from this indexer's column.
        Parameters:
        currEntry - Provides access to the current Row object in the Cursor
        desc - Descriptor object for this dimension within an IncrementalIndex
        Returns:
        A new object that reads rows from currEntry

      • compareUnsortedEncodedKeyComponents

        int compareUnsortedEncodedKeyComponents​(@Nullable
                                        EncodedKeyComponentType lhs,
                                        @Nullable
                                        EncodedKeyComponentType rhs)
        Compares the row values for this DimensionIndexer's dimension from a Row key. The dimension value arrays within a Row key always use the "unsorted" ordering for encoded values. The row values are passed to this function as an Object, the implementer should cast them to the type appropriate for this dimension. For example, a dictionary encoded String implementation would cast the Objects as int[] arrays. When comparing, if the two arrays have different lengths, the shorter array should be ordered first. Otherwise, the implementer of this function should iterate through the unsorted encoded values, converting them to their actual type (e.g., performing a dictionary lookup for a dict-encoded String dimension), and comparing the actual values until a difference is found. Refer to StringDimensionIndexer.compareUnsortedEncodedKeyComponents() for a reference implementation. The comparison rules used by this method should match the rules used by DimensionHandler.getEncodedValueSelectorComparator(), otherwise incorrect ordering/merging of rows can occur during ingestion, causing issues such as imperfect rollup.
        Parameters:
        lhs - dimension value array from a Row key
        rhs - dimension value array from a Row key
        Returns:
        comparison of the two arrays

      • checkUnsortedEncodedKeyComponentsEqual

        boolean checkUnsortedEncodedKeyComponentsEqual​(@Nullable
                                               EncodedKeyComponentType lhs,
                                               @Nullable
                                               EncodedKeyComponentType rhs)
        Check if two row value arrays from Row keys are equal.
        Parameters:
        lhs - dimension value array from a Row key
        rhs - dimension value array from a Row key
        Returns:
        true if the two arrays are equal

      • getUnsortedEncodedKeyComponentHashCode

        int getUnsortedEncodedKeyComponentHashCode​(@Nullable
                                           EncodedKeyComponentType key)
        Given a row value array from a Row key, generate a hashcode.
        Parameters:
        key - dimension value array from a Row key
        Returns:
        hashcode of the array

      • convertUnsortedEncodedKeyComponentToActualList

        Object convertUnsortedEncodedKeyComponentToActualList​(EncodedKeyComponentType key)
        Given a row value array from a Row key, as described in the documentation for compareUnsortedEncodedKeyComponents(EncodedKeyComponentType, EncodedKeyComponentType), convert the unsorted encoded values to a list of actual values. If the key has one element, this method should return a single Object instead of a list.
        Parameters:
        key - dimension value array from a Row key
        Returns:
        single value or list containing the actual values corresponding to the encoded values in the input array

      • fillBitmapsFromUnsortedEncodedKeyComponent

        void fillBitmapsFromUnsortedEncodedKeyComponent​(EncodedKeyComponentType key,
                                                int rowNum,
                                                MutableBitmap[] bitmapIndexes,
                                                BitmapFactory factory)
        Helper function for building bitmap indexes for integer-encoded dimensions. Called by IncrementalIndexAdapter as it iterates through its sequence of rows. Given a row value array from a Row key, with the current row number indicated by "rowNum", set the index for "rowNum" in the bitmap index for each value that appears in the row value array. For example, if key is an int[] array with values [1,3,4] for a dictionary-encoded String dimension, and rowNum is 27, this function would set bit 27 in bitmapIndexes[1], bitmapIndexes[3], and bitmapIndexes[4] See StringDimensionIndexer.fillBitmapsFromUnsortedEncodedKeyComponent() for a reference implementation. If a dimension type does not support bitmap indexes, this function will not be called and can be left unimplemented.
        Parameters:
        key - dimension value array from a Row key
        rowNum - current row number
        bitmapIndexes - array of bitmaps, indexed by integer dimension value
        factory - bitmap factory