Question

在BigQuery中，我们试图运行：

SELECT day, AVG(value)/(1024*1024) FROM ( 
    SELECT value, UTC_USEC_TO_DAY(timestamp) as day, 
         PERCENTILE_RANK() OVER (PARTITION BY day ORDER BY value ASC) as rank 
    FROM [Datastore.PerformanceDatum]
    WHERE type = "MemoryPerf"
) WHERE rank >= 0.9 AND rank <= 0.91 
GROUP BY day 
ORDER BY day desc;

返回相对少量的数据。但我们收到了消息：

Error: Resources exceeded during query execution. The query contained a GROUP BY operator, consider using GROUP EACH BY instead. For more details, please see https://developers.google.com/bigquery/docs/query-reference#groupby

是什么让这个查询失败，子查询的大小？我们可以做一些等效的查询来避免这个问题吗？

编辑以响应注释：如果我添加GROUP EACH BY（并删除外部ORDER BY），则查询失败，声称GROUP EACH BY在这里不可并行化。

Answer 1

我写了一个适合我的等效查询：

SELECT day, AVG(value)/(1024*1024) FROM (
SELECT data value, UTC_USEC_TO_DAY(dtimestamp) as day, 
         PERCENTILE_RANK() OVER (PARTITION BY day ORDER BY value ASC) as rank 
    FROM [io_sensor_data.moscone_io13]
    WHERE sensortype = "humidity"
) WHERE rank >= 0.9 AND rank <= 0.91 
GROUP BY day 
ORDER BY day desc;

如果我只运行内部查询，我得到3,660,624个结果。你的数据集是否大于那个？

外部选择在按天分组时仅给出4个结果。我会尝试不同的分组，看看我是否能达到极限：

SELECT day, AVG(value)/(1024*1024) FROM (
SELECT data value, dtimestamp / 1000 as day, 
         PERCENTILE_RANK() OVER (PARTITION BY day ORDER BY value ASC) as rank 
    FROM [io_sensor_data.moscone_io13]
    WHERE sensortype = "humidity"
) WHERE rank >= 0.9 AND rank <= 0.91 
GROUP BY day 
ORDER BY day desc;

运行，现在有57662个不同的组。

我尝试了不同的组合来获得相同的错误。我能够得到与初始数据量翻倍相同的错误。将数据量翻倍的简单“黑客”正在发生变化：

    FROM [io_sensor_data.moscone_io13]

要：

    FROM [io_sensor_data.moscone_io13], [io_sensor_data.moscone_io13]

然后我得到同样的错误。你有多少数据？你可以申请额外的过滤器吗？由于您已经在白天对percentile_rank进行了分区，您是否可以添加其他查询以仅分析一小部分天（例如，仅在上个月）？

如何使此查询高效运行？

1 个答案: