flink sql upsert kafka对于changelogNormalize state解读

这里说一点：

• flink sql - upsert kafka 去重并非在kafka-connector中实现，而是在这个DeduplicateFunctionBase父类中的ValueState进行keyby状态去重的，因此为何upsert-kafka需要在kafka的message中带有key；

/**
 * Base class for deduplicate function.
 *
 * @param  Type of the value in the state.
 * @param  Type of the key.
 * @param  Type of the input elements.
 * @param  Type of the returned elements.
 */
abstract class DeduplicateFunctionBase<T, K, IN, OUT> extends KeyedProcessFunction<K, IN, OUT> {

    private static final long serialVersionUID = 1L;

    // the TypeInformation of the values in the state.
    protected final TypeInformation<T> typeInfo;
    protected final long stateRetentionTime;
    protected final TypeSerializer<OUT> serializer;
    // state stores previous message under the key.
    protected ValueState<T> state;

    public DeduplicateFunctionBase(
            TypeInformation<T> typeInfo, TypeSerializer<OUT> serializer, long stateRetentionTime) {
        this.typeInfo = typeInfo;
        this.stateRetentionTime = stateRetentionTime;
        this.serializer = serializer;
    }

    @Override
    public void open(Configuration configure) throws Exception {
        super.open(configure);
        ValueStateDescriptor<T> stateDesc =
                new ValueStateDescriptor<>("deduplicate-state", typeInfo);
        StateTtlConfig ttlConfig = createTtlConfig(stateRetentionTime);
        if (ttlConfig.isEnabled()) {
            stateDesc.enableTimeToLive(ttlConfig);
        }
        state = getRuntimeContext().getState(stateDesc);
    }
}

state进行deduplicate具体实现：
org.apache.flink.table.runtime.operators.deduplicate.DeduplicateFunctionHelper

 /**
     * Processes element to deduplicate on keys with process time semantic, sends current element as
     * last row, retracts previous element if needed.
     *
     * @param currentRow latest row received by deduplicate function
     * @param generateUpdateBefore whether need to send UPDATE_BEFORE message for updates
     * @param state state of function, null if generateUpdateBefore is false
     * @param out underlying collector
     */
    static void processLastRowOnProcTime(
            RowData currentRow,
            boolean generateUpdateBefore,
            boolean generateInsert,
            ValueState<RowData> state,
            Collector<RowData> out)
            throws Exception {

        checkInsertOnly(currentRow);
        if (generateUpdateBefore || generateInsert) {
            // use state to keep the previous row content if we need to generate UPDATE_BEFORE
            // or use to distinguish the first row, if we need to generate INSERT
            RowData preRow = state.value();
            state.update(currentRow);
            if (preRow == null) {
                // the first row, send INSERT message
                currentRow.setRowKind(RowKind.INSERT);
                out.collect(currentRow);
            } else {
                if (generateUpdateBefore) {
                    preRow.setRowKind(RowKind.UPDATE_BEFORE);
                    out.collect(preRow);
                }
                currentRow.setRowKind(RowKind.UPDATE_AFTER);
                out.collect(currentRow);
            }
        } else {
            // always send UPDATE_AFTER if INSERT is not needed
            currentRow.setRowKind(RowKind.UPDATE_AFTER);
            out.collect(currentRow);
        }
    }