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我有成千上万的镶木地板文件需要处理。在处理文件之前，我尝试使用 parquet 元数据获取有关文件的各种信息，例如每个分区中的行数、最小值、最大值等。

我尝试使用 dask.delayed 读取元数据，希望在我的集群中分发元数据收集任务，但这似乎会导致 Dask 不稳定。请参阅下面的示例代码片段和节点超时错误。

有没有办法从 Dask 读取镶木地板元数据？我知道 Dask 的“read_parquet”函数有一个“gather_statistics”选项，您可以将其设置为 false 以加快文件读取速度。但是，如果设置为 true，我看不到访问所有 parquet 元数据/统计信息的方法。

示例代码：


@dask.delayed
def get_pf(item_to_read):
     pf = fastparquet.ParquetFile(item_to_read)
     row_groups = pf.row_groups.copy()
     all_stats = pf.statistics.copy()
     col = pf.info['columns'].copy()
     return [row_groups, all_stats, col]

stats_arr = get_pf(item_to_read)

示例错误：

2019-10-03 01:43:51,202 - INFO - 192.168.0.167 - distributed.worker - ERROR - Worker stream died during communication: tcp://192.168.0.223:34623

2019-10-03 01:43:51,203 - INFO - 192.168.0.167 - Traceback (most recent call last):

2019-10-03 01:43:51,204 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/distributed/comm/core.py", line 218, in connect

2019-10-03 01:43:51,206 - INFO - 192.168.0.167 -     quiet_exceptions=EnvironmentError,

2019-10-03 01:43:51,207 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/tornado/gen.py", line 729, in run

2019-10-03 01:43:51,210 - INFO - 192.168.0.167 -     value = future.result()

2019-10-03 01:43:51,211 - INFO - 192.168.0.167 - tornado.util.TimeoutError: Timeout

2019-10-03 01:43:51,212 - INFO - 192.168.0.167 -

2019-10-03 01:43:51,213 - INFO - 192.168.0.167 - During handling of the above exception, another exception occurred:

2019-10-03 01:43:51,214 - INFO - 192.168.0.167 -

2019-10-03 01:43:51,215 - INFO - 192.168.0.167 - Traceback (most recent call last):

2019-10-03 01:43:51,217 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/distributed/worker.py", line 1841, in gather_dep

2019-10-03 01:43:51,218 - INFO - 192.168.0.167 -     self.rpc, deps, worker, who=self.address

2019-10-03 01:43:51,219 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/tornado/gen.py", line 729, in run

2019-10-03 01:43:51,220 - INFO - 192.168.0.167 -     value = future.result()

2019-10-03 01:43:51,222 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/tornado/gen.py", line 736, in run

2019-10-03 01:43:51,223 - INFO - 192.168.0.167 -     yielded = self.gen.throw(*exc_info)  # type: ignore

2019-10-03 01:43:51,224 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/distributed/worker.py", line 3029, in get_data_from_worker

2019-10-03 01:43:51,225 - INFO - 192.168.0.167 -     comm = yield rpc.connect(worker)

2019-10-03 01:43:51,640 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/tornado/gen.py", line 729, in run

2019-10-03 01:43:51,641 - INFO - 192.168.0.167 -     value = future.result()

2019-10-03 01:43:51,643 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/tornado/gen.py", line 736, in run

2019-10-03 01:43:51,644 - INFO - 192.168.0.167 -     yielded = self.gen.throw(*exc_info)  # type: ignore

2019-10-03 01:43:51,645 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/distributed/core.py", line 866, in connect

2019-10-03 01:43:51,646 - INFO - 192.168.0.167 -     connection_args=self.connection_args,

2019-10-03 01:43:51,647 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/tornado/gen.py", line 729, in run

2019-10-03 01:43:51,649 - INFO - 192.168.0.167 -     value = future.result()

2019-10-03 01:43:51,650 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/tornado/gen.py", line 736, in run

2019-10-03 01:43:51,651 - INFO - 192.168.0.167 -     yielded = self.gen.throw(*exc_info)  # type: ignore

2019-10-03 01:43:51,652 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/distributed/comm/core.py", line 230, in connect

2019-10-03 01:43:51,653 - INFO - 192.168.0.167 -     _raise(error)

2019-10-03 01:43:51,654 - INFO - 192.168.0.167 -   File "/usr/local/lib/python3.7/dist-packages/distributed/comm/core.py", line 207, in _raise

2019-10-03 01:43:51,656 - INFO - 192.168.0.167 -     raise IOError(msg)

2019-10-03 01:43:51,657 - INFO - 192.168.0.167 - OSError: Timed out trying to connect to 'tcp://192.168.0.223:34623' after 10 s: connect() didn't finish in time
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1 回答 1

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dd.read_parquet需要很长时间吗？如果没有，那么您可以按照其中的任何策略在客户端进行阅读。

如果数据在根目录中有一个_metadata文件，那么您可以简单地使用 fastparquet 打开它，这正是 Dask 会做的。它包含所有数据片段的所有详细信息。

分发元数据读取没有什么特别的原因，但您应该知道，在某些情况下，总元数据项可能会增加相当大的大小。

于 2019-10-03T14:01:03.060 回答