java - 将 Kafka 与 Apache Calcite 集成

Question

我正在尝试将方解石与 Kafka 集成，我引用了 CsvStreamableTable。

每个 ConsumerRecord 都使用下面的代码转换为 Object[]:

static class ArrayRowConverter extends RowConverter<Object[]> {
    private List<Schema.Field> fields;

    public ArrayRowConverter(List<Schema.Field> fields) {
        this.fields = fields;
    }

    @Override
    Object[] convertRow(ConsumerRecord<String, GenericRecord> consumerRecord) {
        Object[] objects = new Object[fields.size()+1];
        int i = 0 ;
        objects[i++] = consumerRecord.timestamp();
        for(Schema.Field field : this.fields) {
            Object obj = consumerRecord.value().get(field.name());
            if( obj instanceof Utf8 ){
                objects[i ++] = obj.toString();
            }else {
                objects[i ++] = obj;
            }
        }
        return objects;
    }
}

Enumerator的实现如下，一个线程不断地从kafka轮询记录并将它们放入队列中，getRecord()方法从该队列轮询:

public E current() {
    return current;
}

public boolean moveNext() {
for(;;) {
    if(cancelFlag.get()) {
        return false;
    }
    ConsumerRecord<String, GenericRecord> record = getRecord();
    if(record ==  null) {
        try {
            Thread.sleep(200L);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        continue;
    }
    current = rowConvert.convertRow(record);
    return true;
    }
}

我测试了SELECT STREAM * FROM Kafka.clicks，它工作正常。rowtime是显式添加的第一列，值为Kafka的记录时间戳。

但是当我尝试

SELECT STREAM FLOOR(rowtime TO HOUR) 
AS rowtime,ip,COUNT(*) AS c FROM KAFKA.clicks  GROUP BY FLOOR(rowtime TO HOUR), ip

抛出异常

java.sql.SQLException: Error while executing SQL "SELECT STREAM FLOOR(rowtime TO HOUR) AS rowtime,ip,COUNT(*) AS c FROM KAFKA.clicks  GROUP BY FLOOR(rowtime TO HOUR), ip": From line 1, column 85 to line 1, column 119: Streaming aggregation requires at least one monotonic expression in GROUP BY clause
    at org.apache.calcite.avatica.Helper.createException(Helper.java:56)
    at org.apache.calcite.avatica.Helper.createException(Helper.java:41)

Answer 1

您需要声明“ROWTIME”列是单调的。在 MockCatalogReader 中，请注意如何在“ORDERS”和“SHIPMENTS”流中将“ROWTIME”声明为单调的。这就是为什么 SqlValidatorTest.testStreamGroupBy() 中的某些查询有效而其他查询无效的原因。 validator 依赖的关键方法是SqlValidatorTable.getMonotonicity(String columnName)。