Package org.apache.druid.segment.column

Class TypeStrategies.StringTypeStrategy

  • All Implemented Interfaces:
    it.unimi.dsi.fastutil.Hash.Strategy<String>, Comparator<Object>, TypeStrategy<String>
    Enclosing class:
    TypeStrategies
    public static final class TypeStrategies.StringTypeStrategy
extends Object
implements TypeStrategy<String>
    Read and write non-null UTF8 encoded String values. Encodes the length in bytes as an integer prefix followed by the actual encoded value bytes. format: | length (int) | bytes |

    • Constructor Detail

      • StringTypeStrategy

        public StringTypeStrategy()

    • Method Detail

      • estimateSizeBytes

        public int estimateSizeBytes​(String value)
        Description copied from interface: TypeStrategy
        Estimate the size in bytes that writing this value to memory would require. This method is not required to be exactly correct, but many implementations might be. Implementations should err on the side of over-estimating if exact sizing is not efficient. Example usage of this method is estimating heap memory usage for an aggregator or the amount of buffer which might need allocated to then TypeStrategy.write(java.nio.ByteBuffer, T, int) a value
        Specified by:
        estimateSizeBytes in interface TypeStrategy<String>

      • write

        public int write​(ByteBuffer buffer,
                 String value,
                 int maxSizeBytes)
        Description copied from interface: TypeStrategy
        Write a non-null value to the ByteBuffer at position Buffer.position(). This will move the underlying position by the size of the value written. This method returns the number of bytes written. If writing the value would take more than 'maxSizeBytes', this method will return a negative value indicating the number of additional bytes that would be required to fully write the value. Partial results may be written to the buffer when in this state, and the position may be left at whatever point the implementation ran out of space while writing the value. Callers should save the starting position if it is necessary to 'rewind' after a partial write. Callers MUST check that the return value is positive which indicates a successful write, while a negative response a partial write.
        Specified by:
        write in interface TypeStrategy<String>
        Returns:
        number of bytes written

      • groupable

        public boolean groupable()
        Description copied from interface: TypeStrategy
        Whether the type is groupable or not. This is always true for all the primitive types, arrays, and nested arrays therefore the SQL and the native layer might ignore this flag for those types. For complex types, this flag can be true or false, depending on whether the semantics and implementation of the type naturally leads to groupability or not. For example, it makes sense for JSON columns to be groupable, however there is little sense in grouping sketches (before finalizing).

        If a type is groupable, following statements MUST hold:

        a. TypeStrategy.equals(Object, Object) must be implemented. It should return true if and only if two objects are equal and can be grouped together.

        b. TypeStrategy.hashCode(Object) must be implemented, and must be consistent with equals. It should return a hashCode for the given object. For two objects that are equal, it must return the same hash value. For two objects that are not equal, it can return the same hash value (or not). A conscious effort must be made to minimise collisions between the hash values of two non-equal objects for faster grouping.

        c. Comparator.compare(Object, Object) must be consistent with equals. Apart from abiding by the definition of Comparator.compare(T, T), it must not return 0 for two objects that are not equals, and converse must also hold, i.e. if the value returned by compare is not zero, then the arguments must not be equal.

        Specified by:
        groupable in interface TypeStrategy<String>