Module org.elasticsearch.server

Package org.elasticsearch.index.codec.tsdb.pipeline.numeric.stages

Class DeltaCodecStage

java.lang.Object

org.elasticsearch.index.codec.tsdb.pipeline.numeric.stages.DeltaCodecStage

All Implemented Interfaces:

NumericCodecStage, TransformDecoder, TransformEncoder

public final class DeltaCodecStage
extends Object
implements NumericCodecStage

Delta encoding transform stage for monotonic sequences.

Effectiveness

Applied only when the sequence is monotonic (at least 2 increases with 0 decreases, or at least 2 decreases with 0 increases). Non-monotonic or constant sequences are skipped because deltas would not reduce the dynamic range.

Example

Monotonic ascending [100, 200, 350, 500] produces deltas [100, 150, 150] with first value 100 stored as metadata.

Metadata layout

Written to the stage metadata section (see BlockFormat):

   +---------------------+
   | ZLong(first)        |  1-10 bytes, zigzag-encoded first value
   +---------------------+
 

Zigzag encoding ensures small absolute values (both positive and negative) use few bytes, which is typical for the starting point of a monotonic sequence.

Field Summary

Fields

Modifier and Type	Field	Description
static final DeltaCodecStage	INSTANCE	Singleton instance.

Method Summary

Modifier and Type	Method	Description
void	decode(long[] values, int valueCount, DecodingContext context)	Reverses the transformation on values in-place using metadata from the context.
static void	decodeStatic(DeltaCodecStage stage, long[] values, int valueCount, DecodingContext context)
void	encode(long[] values, int valueCount, EncodingContext context)	Transforms values in-place and writes any metadata to the context.
static void	encodeStatic(DeltaCodecStage stage, long[] values, int valueCount, EncodingContext context)
byte	id()	Returns the unique stage identifier.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

INSTANCE

public static final DeltaCodecStage INSTANCE

Singleton instance.

Method Details

id

public byte id()

Description copied from interface: TransformEncoder

Returns the unique stage identifier.

Specified by:

id in interface TransformDecoder

Specified by:

id in interface TransformEncoder

Returns:

the stage ID byte

encode

public void encode(long[] values,
 int valueCount,
 EncodingContext context)

Description copied from interface: TransformEncoder

Transforms values in-place and writes any metadata to the context.

If the stage determines that the transformation would not be effective, it may return without modifying the values or writing metadata. The pipeline checks EncodingContext.isStageApplied(int) to detect this.

Specified by:

encode in interface TransformEncoder

Parameters:

values - the values to transform in-place

valueCount - the number of valid values in the array

context - the encoding context for metadata and stage tracking

decode

public void decode(long[] values,
 int valueCount,
 DecodingContext context)
            throws IOException

Description copied from interface: TransformDecoder

Reverses the transformation on values in-place using metadata from the context.

Specified by:

decode in interface TransformDecoder

Parameters:

values - the values to reverse-transform in-place

valueCount - the number of valid values in the array

context - the decoding context for reading stage metadata

Throws:

IOException - if an I/O error occurs while reading metadata

encodeStatic

public static void encodeStatic(DeltaCodecStage stage,
 long[] values,
 int valueCount,
 EncodingContext context)
                         throws IOException

Throws:

IOException

decodeStatic

public static void decodeStatic(DeltaCodecStage stage,
 long[] values,
 int valueCount,
 DecodingContext context)
                         throws IOException

Throws:

IOException