Implementation:Apache Shardingsphere ColumnShadowAlgorithm SPI

Knowledge Sources	Apache_Shardingsphere Shadow Algorithm
Domains	Shadow_Testing, SPI, SQL_Routing
Last Updated	2026-02-10 00:00 GMT

Overview

SPI interface for column-value-based shadow routing algorithms.

Description

ColumnShadowAlgorithm<T> is a generic interface extending ShadowAlgorithm that defines the contract for shadow algorithms based on column values in SQL statements. Implementors decide whether a SQL statement targets a shadow data source by examining the value of a designated shadow column.

Usage

Implement this interface when creating shadow algorithms that route based on column values (e.g., a shadow_flag column in INSERT/UPDATE/SELECT/DELETE statements).

Code Reference

Source Location

• Repository: Apache_Shardingsphere
• File: features/shadow/api/src/main/java/org/apache/shardingsphere/shadow/spi/column/ColumnShadowAlgorithm.java
• Lines: 1-51

Signature

public interface ColumnShadowAlgorithm<T> extends ShadowAlgorithm {

    boolean isShadow(Collection<String> shadowTableNames, PreciseColumnShadowValue<T> shadowValue);

    String getShadowColumn();

    ShadowOperationType getShadowOperationType();
}

Import

import org.apache.shardingsphere.shadow.spi.column.ColumnShadowAlgorithm;

I/O Contract

Inputs

Name	Type	Required	Description
shadowTableNames	Collection<String>	Yes	Names of configured shadow tables
shadowValue	PreciseColumnShadowValue<T>	Yes	Column value context including table name, operation type, column name, and value

Outputs

Name	Type	Description
isShadow() returns	boolean	True if the statement should route to shadow data source
getShadowColumn() returns	String	The column name used for shadow determination
getShadowOperationType() returns	ShadowOperationType	The SQL operation type this algorithm handles

Usage Examples

import org.apache.shardingsphere.shadow.spi.column.ColumnShadowAlgorithm;
import org.apache.shardingsphere.shadow.spi.column.PreciseColumnShadowValue;
import org.apache.shardingsphere.shadow.spi.ShadowOperationType;

public final class ColumnValueMatchedShadowAlgorithm implements ColumnShadowAlgorithm<Comparable<?>> {

    @Override
    public boolean isShadow(final Collection<String> shadowTableNames,
                            final PreciseColumnShadowValue<Comparable<?>> shadowValue) {
        return shadowTableNames.contains(shadowValue.getTableName())
                && getShadowOperationType() == shadowValue.getShadowOperationType()
                && getShadowColumn().equals(shadowValue.getColumnName())
                && matchesValue(shadowValue.getValue());
    }

    @Override
    public String getShadowColumn() {
        return "shadow_flag";
    }

    @Override
    public ShadowOperationType getShadowOperationType() {
        return ShadowOperationType.INSERT;
    }

    private boolean matchesValue(final Comparable<?> value) {
        return "1".equals(String.valueOf(value));
    }
}

Related Pages

• Principle:Apache_Shardingsphere_Column_Based_Routing