FlinkSQL ChangeLog

01 Changelog相关优化规则

0101 运行upsert-kafka作业

登录sql-client，创建一个upsert-kafka的sql作业（注意，这里发送给kafka的消息必须带key，普通只有value的消息无法解析，这里的key即是主键的值）

CREATE TABLE pageviews_per_region (
  user_region STRING,
  pv STRING,
  PRIMARY KEY (user_region) NOT ENFORCED  -- 设置主键
) WITH (
  'connector' = 'upsert-kafka',
  'topic' = 'pageviews_per_region',
  'properties.bootstrap.servers' = 'xxxxxx:9092',
  'key.format' = 'csv',
  'value.format' = 'csv'
);

select * from pageviews_per_region;
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发送消息带key和消费消息显示key方式如下

kafka-console-producer.sh --broker-list xxxxxx:9092 --topic pageviews_per_region --property "parse.key=true" --property "key.separator=:"
key1:value1,value1
key2:value2,value2

kafka-console-consumer.sh --bootstrap-server xxxxxx:9092 --topic pageviews_per_region --from-beginning --property print.key=true
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作业的DAG图如下

0102 StreamPhysicalChangelogNormalize

DAG图中有一个ChangelogNormalize，代码中搜索到对应的类是StreamPhysicalChangelogNormalize，这是一个对changelog数据做规范化的类，注释如下

/**
 * Stream physical RelNode which normalizes a changelog stream which maybe an upsert stream or a
 * changelog stream containing duplicate events. This node normalize such stream into a regular
 * changelog stream that contains INSERT/UPDATE_BEFORE/UPDATE_AFTER/DELETE records without
 * duplication.
 */
class StreamPhysicalChangelogNormalize(
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功能就是转成对应的exec节点

override def translateToExecNode(): ExecNode[_] = {
  val generateUpdateBefore = ChangelogPlanUtils.generateUpdateBefore(this)
  new StreamExecChangelogNormalize(
    unwrapTableConfig(this),
    uniqueKeys,
    generateUpdateBefore,
    InputProperty.DEFAULT,
    FlinkTypeFactory.toLogicalRowType(getRowType),
    getRelDetailedDescription)
}
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0103 StreamPhysicalTableSourceScanRule

StreamPhysicalChangelogNormalize是在优化规则StreamPhysicalTableSourceScanRule当中创建的，如下流式的FlinkLogicalTableSourceScan会应用该规则

class StreamPhysicalTableSourceScanRule
  extends ConverterRule(
    classOf[FlinkLogicalTableSourceScan],
    FlinkConventions.LOGICAL,
    FlinkConventions.STREAM_PHYSICAL,
    "StreamPhysicalTableSourceScanRule") {
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创建StreamPhysicalChangelogNormalize，也就是转为changelog的条件如下

if (
  isUpsertSource(resolvedSchema, table.tableSource) ||
  isSourceChangeEventsDuplicate(resolvedSchema, table.tableSource, config)
) {
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isUpsertSource判断是否为upsert流，判断逻辑如下

public static boolean isUpsertSource(
        ResolvedSchema resolvedSchema, DynamicTableSource tableSource) {
    if (!(tableSource instanceof ScanTableSource)) {
        return false;
    }
    ChangelogMode mode = ((ScanTableSource) tableSource).getChangelogMode();
    boolean isUpsertMode =
            mode.contains(RowKind.UPDATE_AFTER) && !mode.contains(RowKind.UPDATE_BEFORE);
    boolean hasPrimaryKey = resolvedSchema.getPrimaryKey().isPresent();
    return isUpsertMode && hasPrimaryKey;
}
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其中ChangelogMode在各自数据源实现类的getChangelogMode接口中定义，如JDBC只支持insert

@Override
public ChangelogMode getChangelogMode() {
    return ChangelogMode.insertOnly();
}
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isSourceChangeEventsDuplicate判断不是upsert的更改流，判断逻辑如下

public static boolean isSourceChangeEventsDuplicate(
        ResolvedSchema resolvedSchema,
        DynamicTableSource tableSource,
        TableConfig tableConfig) {
    if (!(tableSource instanceof ScanTableSource)) {
        return false;
    }
    ChangelogMode mode = ((ScanTableSource) tableSource).getChangelogMode();
    boolean isCDCSource =
            !mode.containsOnly(RowKind.INSERT) && !isUpsertSource(resolvedSchema, tableSource);
    boolean changeEventsDuplicate =
            tableConfig.get(ExecutionConfigOptions.TABLE_EXEC_SOURCE_CDC_EVENTS_DUPLICATE);
    boolean hasPrimaryKey = resolvedSchema.getPrimaryKey().isPresent();
    return isCDCSource && changeEventsDuplicate && hasPrimaryKey;
}
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综合来说要走StreamPhysicalChangelogNormalize这一条调用链，就不能是insertOnly的数据源，但目前大部分Flink实现的数据源包括Iceberg都是insertOnly的

0104 更新模式

Flink相关的更新模式类有如下几个：RowKind、ChangelogMode、UpdateKind

• RowKind

RowKind是定义更新流每条数据的类型，其中对于更新有；两条数据，一条删除旧数据，一条插入新数据

/** Insertion operation. */
INSERT("+I", (byte) 0),

/**
 * Update operation with the previous content of the updated row.
 *
 * 
This kind SHOULD occur together with {@link #UPDATE_AFTER} for modelling an update that
 * needs to retract the previous row first. It is useful in cases of a non-idempotent update,
 * i.e., an update of a row that is not uniquely identifiable by a key.
 */
UPDATE_BEFORE("-U", (byte) 1),

/**
 * Update operation with new content of the updated row.
 *
 * 
This kind CAN occur together with {@link #UPDATE_BEFORE} for modelling an update that
 * needs to retract the previous row first. OR it describes an idempotent update, i.e., an
 * update of a row that is uniquely identifiable by a key.
 */
UPDATE_AFTER("+U", (byte) 2),

/** Deletion operation. */
DELETE("-D", (byte) 3);
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• ChangelogMode

ChangelogMode定义数据源的更新模式，主要三种，就是包含不同的RowKind的类型

private static final ChangelogMode INSERT_ONLY =
        ChangelogMode.newBuilder().addContainedKind(RowKind.INSERT).build();

private static final ChangelogMode UPSERT =
        ChangelogMode.newBuilder()
                .addContainedKind(RowKind.INSERT)
                .addContainedKind(RowKind.UPDATE_AFTER)
                .addContainedKind(RowKind.DELETE)
                .build();

private static final ChangelogMode ALL =
        ChangelogMode.newBuilder()
                .addContainedKind(RowKind.INSERT)
                .addContainedKind(RowKind.UPDATE_BEFORE)
                .addContainedKind(RowKind.UPDATE_AFTER)
                .addContainedKind(RowKind.DELETE)
                .build();
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• UpdateKind

UpdateKind是针对update这种更新类型细分

/** NONE doesn't represent any kind of update operation. */
NONE,

/**
 * This kind indicates that operators should emit update changes just as a row of {@code
 * RowKind#UPDATE_AFTER}.
 */
ONLY_UPDATE_AFTER,

/**
 * This kind indicates that operators should emit update changes in the way that a row of {@code
 * RowKind#UPDATE_BEFORE} and a row of {@code RowKind#UPDATE_AFTER} together.
 */
BEFORE_AND_AFTER
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02 StreamExecChangelogNormalize

StreamExecChangelogNormalize的处理流程中根据是否启用table.exec.mini-batch.enabled分为微批处理和单数据的流处理

微批处理使用ProcTimeMiniBatchDeduplicateKeepLastRowFunction，流式使用ProcTimeDeduplicateKeepLastRowFunction，两者的核心差别就是微批会缓存数据使用一个for循环处理

这两个函数除了StreamPhysicalChangelogNormalize这一条链路外，还有StreamExecDeduplicate这一条链路，对应StreamPhysicalRankRule，是一个排序的东西

for (Map.Entry<RowData, RowData> entry : buffer.entrySet()) {
    RowData currentKey = entry.getKey();
    RowData currentRow = entry.getValue();
    ctx.setCurrentKey(currentKey);
    if (inputInsertOnly) {
        processLastRowOnProcTime(
                currentRow,
                generateUpdateBefore,
                generateInsert,
                state,
                out,
                isStateTtlEnabled,
                equaliser);
    } else {
        processLastRowOnChangelog(
                currentRow, generateUpdateBefore, state, out, isStateTtlEnabled, equaliser);
    }
}
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• processLastRowOnProcTime

对数据按照时间语义进行去重，将当前数据作为最新，这个函数只针对insert only的数据

static void checkInsertOnly(RowData currentRow) {
    Preconditions.checkArgument(currentRow.getRowKind() == RowKind.INSERT);
}
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整套处理逻辑就是对数据根据场景修改数据的RowKind类型

} else {
    if (generateUpdateBefore) {
        preRow.setRowKind(RowKind.UPDATE_BEFORE);
        out.collect(preRow);
    }
    currentRow.setRowKind(RowKind.UPDATE_AFTER);
    out.collect(currentRow);
}
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• processLastRowOnChangelog

这个函数就是按Key去重，本质上也是针对数据修改RowKind

核心的一块功能就是更新的时候要将前一个数据修改为UPDATE_BEFORE

} else {
    if (generateUpdateBefore) {
        preRow.setRowKind(RowKind.UPDATE_BEFORE);
        out.collect(preRow);
    }
    currentRow.setRowKind(RowKind.UPDATE_AFTER);
    out.collect(currentRow);
}
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函数整体借用的是Flink的state功能，从状态中获取前面的数据，所以对状态缓存由要求；另外针对非删除型的数据，如果TTL没有开的话，就不会更新前面的数据

if (!isStateTtlEnabled && equaliser.equals(preRow, currentRow)) {
    // currentRow is the same as preRow and state cleaning is not enabled.
    // We do not emit retraction and update message.
    // If state cleaning is enabled, we have to emit messages to prevent too early
    // state eviction of downstream operators.
    return;
}
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03 初始RowKind来源

前面的流程里，在进行changelog转换的时候，数据是已经存在一个RowKind的值了，这一章追踪初始RowKind的来源

基于Flink-27的设计，Kafka数据源处理任务有一个KafkaRecordEmitter，emitRecord当中做数据的反序列化

deserializationSchema.deserialize(consumerRecord, sourceOutputWrapper);
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最终走到DeserializationSchema.deserialize完成最终的反序列化

default void deserialize(byte[] message, Collector<T> out) throws IOException {
    T deserialize = deserialize(message);
    if (deserialize != null) {
        out.collect(deserialize);
    }
}
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这里message是一个二进制数组，实际是Kafka的数据类型ConsumerRecord。根据SQL当中的配置，value反序列化使用的是csv，所以走到CsvRowDataDeserializationSchema当中处理

final JsonNode root = objectReader.readValue(message);
return (RowData) runtimeConverter.convert(root);
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这里读出来的root是数据的key，convert的转化的实现类是CsvToRowDataConverters，其createRowConverter接口当中创建了转化函数，函数中将数据转化为了Flink的数据类型GenericRowData

GenericRowData row = new GenericRowData(arity);
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GenericRowData的定义当中，有初始化RowKind，就是insert

public GenericRowData(int arity) {
    this.fields = new Object[arity];
    this.kind = RowKind.INSERT; // INSERT as default
}
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04 补充

0401 delete

按照官方说法，发送一个空消息就会产生delete

 Also, null values are interpreted in a special way: a record with a null value represents a “DELETE”.
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使用kafka producer控制台发送空消息无法解析

[ERROR] Could not execute SQL statement. Reason:
org.apache.flink.shaded.jackson2.com.fasterxml.jackson.databind.exc.MismatchedInputException: No content to map due to end-of-input
 at [Source: UNKNOWN; byte offset: #UNKNOWN]
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官方说法是kafka的控制台版本对 null的支持问题，需要3.2以上版本
https://issues.apache.org/jira/browse/FLINK-27663?jql=project%20%3D%20FLINK%20AND%20text%20~%20%22upsert-kafka%22

空值处理逻辑在DynamicKafkaDeserializationSchema.deserialize当中
这里根据输入的数据是否空值进行分支处理；非空值时走的就是前三章的逻辑，也就是这里是前三章逻辑的入口

if (record.value() == null && upsertMode) {
    // collect tombstone messages in upsert mode by hand
    outputCollector.collect(null);
} else {
    valueDeserialization.deserialize(record.value(), outputCollector);
}
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空值时走到OutputProjectionCollector.emitRow，这里会设置初始类型为DELETE

if (physicalValueRow == null) {
    if (upsertMode) {
        rowKind = RowKind.DELETE;
    } else {
        throw new DeserializationException(
                "Invalid null value received in non-upsert mode. Could not to set row kind for output record.");
    }
} else {
    rowKind = physicalValueRow.getRowKind();
}
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