Package org.apache.druid.query.rowsandcols.semantic

Interface WireTransferable

All Known Implementing Classes:

FrameWireTransferable

public interface WireTransferable

A Semantic interface that enables serializing a RowsAndColumns over the wire.

Serialization and Deserialization are a weird beast. It is very easy to follow an Object-Oriented mechanism for serializing out an object, but when you want to deserialize, it is unclear exactly which class should be deserialized. This requires extra metadata that helps point the deserializing code to how to interpret the bytes.

The WireTransferable works by serializing the object as a singular byte array, the first byte of the byte array is interpretted as an unsigned integer (N) and represents the length of the "extra metadata" to identify the correct deserializer. Those N bytes are read as a utf8 String and used to look up the deserialization logic. This identifier must be registered with DruidSecondaryModule.getWireTransferableDeserializerBinder(com.google.inject.Binder), which will use the identifier to look up the logic and deserialize the RowsAndColumns object.

There is, intentionally, no default implementation of WireTransferable that just wraps a RowsAndColumns, this is because the point at which data is transfered over the wire tends to be a very sensitive point in terms of what the best format for transmission is and what optimizations are available. As such, we don't want a concrete class that makes its way to the wire to accidentally get a least-common-denominator serialization and instead want it to be explicitly chosen.

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static class	WireTransferable.ByteArrayOffsetAndLen	A holder class for a byte array, offset and length, this exists to minimize copies.
static class	WireTransferable.ConcreteDeserializer
static interface	WireTransferable.Deserializer

Method Summary

Modifier and Type	Method	Description
WireTransferable.ByteArrayOffsetAndLen	serializedBytes(com.fasterxml.jackson.databind.ObjectMapper mapper)	Serializes the object into bytes.

Method Details

serializedBytes

WireTransferable.ByteArrayOffsetAndLen serializedBytes(com.fasterxml.jackson.databind.ObjectMapper mapper)
                                                throws IOException

Serializes the object into bytes. This method is passed a jackson ObjectMapper that can be used to serialize objects if needed. In general, it's better to generate binary serializations and not rely on the mapper but it's there as an expediency layer to support some compatibility stuff. Hopefully it goes away at some point.

Parameters:

mapper - ObjectMapper

Returns:

bytes that represent the wire-format of this object

Throws:

IOException - a problem with IO