Cassandra CDC idempotent consumer

CdcCommitLogReadHandler.java

package com.waitingforcode.cassandra_cdc;

import org.apache.cassandra.config.ColumnDefinition;
import org.apache.cassandra.db.Clustering;
import org.apache.cassandra.db.Mutation;
import org.apache.cassandra.db.commitlog.CommitLogDescriptor;
import org.apache.cassandra.db.commitlog.CommitLogReadHandler;
import org.apache.cassandra.db.partitions.PartitionUpdate;
import org.apache.cassandra.db.rows.Cell;
import org.apache.cassandra.db.rows.Row;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class CdcCommitLogReadHandler implements CommitLogReadHandler {

    public boolean shouldSkipSegmentOnError(CommitLogReadException e) throws IOException {
        System.out.println("Should skip segment error ?");
        e.printStackTrace();
        return false;
    }

    public void handleUnrecoverableError(CommitLogReadException e) throws IOException {
        e.printStackTrace();
    }

    public void handleMutation(Mutation mutation, int size, int entryLocation, CommitLogDescriptor commitLogDescriptor) {
        for (PartitionUpdate partitionUpdate : mutation.getPartitionUpdates()) {
            if (partitionUpdate.metadata().ksName.equals("cdc_test")) {
                String rowKey = partitionUpdate.metadata().getKeyValidator().getString(partitionUpdate.partitionKey().getKey());
                List<String> values = new ArrayList<>();
                values.add(partitionUpdate.metadata().partitionKeyColumns().toString()+"="+rowKey);
                partitionUpdate.unfilteredIterator().forEachRemaining(partitionRow -> {
                    Row row = partitionUpdate.getRow((Clustering) partitionRow.clustering());

                    Iterator<Cell> cells = row.cells().iterator();
                    Iterator<ColumnDefinition> columns = row.columns().iterator();
                    while (cells.hasNext() && columns.hasNext()) {
                        ColumnDefinition definition = columns.next();
                        Cell cell = cells.next();
                        values.add(definition.name.toString()+"="+definition.type.getString(cell.value()));
                    }

                    System.out.println("Got new row="+values);
                });
            }
        }
    }
}

commands.md

Cluster setup:

ccm remove cdc_cluster
ccm create cdc_cluster -v 3.11.3
ccm populate -n 1
ccm node1 start

Init data

ccm node1 cqlsh
 CREATE KEYSPACE cdc_test  WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 1};
 USE cdc_test;
 CREATE TABLE orders (id int, amount double, first_order boolean, PRIMARY KEY(id)) WITH cdc=true;
 INSERT INTO  orders (id, amount, first_order) VALUES (1, 100, true) IF NOT EXISTS;
 INSERT INTO orders (id, amount, first_order) VALUES (2, 100, false) IF NOT EXISTS;
 INSERT INTO orders (id, amount, first_order) VALUES (3, 100, true) IF NOT EXISTS;
 INSERT INTO orders (id, amount, first_order) VALUES (4, 100, false) IF NOT EXISTS;  
 INSERT INTO  orders (id, amount, first_order) VALUES (5, 100, true) IF NOT EXISTS;
 INSERT INTO orders (id, amount, first_order) VALUES (6, 100, false) IF NOT EXISTS;
 INSERT INTO orders (id, amount, first_order) VALUES (7, 100, true) IF NOT EXISTS;
 INSERT INTO orders (id, amount, first_order) VALUES (8, 100, false) IF NOT EXISTS;  

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.waitingforcode</groupId>
    <artifactId>cassandra-cdc</artifactId>
    <version>1.0-SNAPSHOT</version>
    <project>
        <properties>
            <maven.compiler.source>1.8</maven.compiler.source>
            <maven.compiler.target>1.8</maven.compiler.target>
        </properties>
    </project>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

    <dependencies>
        <dependency>
            <groupId>org.apache.cassandra</groupId>
            <artifactId>cassandra-all</artifactId>
            <version>3.11.3</version>
        </dependency>
        <dependency>
            <groupId>com.datastax.cassandra</groupId>
            <artifactId>cassandra-driver-core</artifactId>
            <version>3.4.0</version>
        </dependency>
    </dependencies>

</project>

Reader.java

// Inspired from https://github.com/smartcat-labs/cassandra-kafka-connector/blob/master/cassandra-cdc/src/main/java/io/smartcat/cassandra/cdc/Reader.java
public class Reader {

    private final WatchService watcher;
    private final Path dir;
    private final WatchKey key;
    private final CommitLogReader commitLogReader;
    private final CdcCommitLogReadHandler commitLogReadHandler;

    public Reader() throws IOException {
        this.dir = Paths.get("/home/bartosz/.ccm/cdc_cluster/node1/cdc_raw");
        watcher = FileSystems.getDefault().newWatchService();
        key = dir.register(watcher, ENTRY_CREATE, ENTRY_MODIFY);
        commitLogReader = new CommitLogReader();
        commitLogReadHandler = new CdcCommitLogReadHandler();
        System.setProperty("cassandra.config", "file:///home/bartosz/.ccm/cdc_cluster/node1/conf/cassandra.yaml");
        DatabaseDescriptor.toolInitialization();
        Schema.instance.loadFromDisk(false);
    }

    public void processEvents() throws InterruptedException, IOException {
        System.out.println("Processing events");
        while (true) {
            WatchKey aKey = watcher.take();
            if (!key.equals(aKey)) {
                System.out.println("WatchKey not recognized.");
                continue;
            }
            for (WatchEvent<?> event : key.pollEvents()) {
                WatchEvent.Kind<?> kind = event.kind();
                if (kind != ENTRY_CREATE) {
                    continue;
                }

                // Context for directory entry event is the file name of entry
                WatchEvent<Path> ev = (WatchEvent<Path>) event;
                Path relativePath = ev.context();
                Path absolutePath = dir.resolve(relativePath);
                processCommitLogSegment(absolutePath);
                //Files.delete(absolutePath);

                // print out event
                System.out.println(event.kind().name() + " for " +  absolutePath);
            }
            key.reset();
        }
    }

    public static void main(String[] args) throws IOException, InterruptedException {
        new Reader().processEvents();
    }

    private void processCommitLogSegment(Path path) throws IOException {
        System.out.println("Processing commitlog segment..."+path.getFileName().toAbsolutePath());
        commitLogReader.readCommitLogSegment(commitLogReadHandler, path.toFile(), false);
        System.out.println("Commitlog segment processed.");
    }
}