Pandas Segfault when reading Parquet data

[mrocklin]

I'm playing with the criteo data and am getting an odd segfault from within Pandas even when on a single thread

>>> import dask.dataframe as dd
>>> import dask
>>> dask.set_options(get=dask.async.get_sync)
<dask.context.set_options object at 0x7ffff6474be0>
>>> df = dd.read_parquet('day-0.parquet')
>>> df.head()

Program received signal SIGBUS, Bus error.
0x00007fffec39f443 in __pyx_f_6pandas_5algos_take_1d_object_object_memview (
    __pyx_optional_args=<synthetic pointer>, __pyx_v_values=..., __pyx_v_indexer=..., __pyx_v_out=...)
   from /home/mrocklin/Software/anaconda/lib/python3.6/site-packages/pandas/algos.cpython-36m-x86_64-linux-gnu.so
(gdb) up
#1  __pyx_pf_6pandas_5algos_380take_1d_object_object (__pyx_self=<optimized out>, 
    __pyx_v_fill_value=0x7ffff7f61fa8, __pyx_v_out=..., __pyx_v_indexer=..., __pyx_v_values=<optimized out>)
    at pandas/algos.c:2818
2818	pandas/algos.c: No such file or directory.
(gdb) up
#2  __pyx_pw_6pandas_5algos_381take_1d_object_object (__pyx_self=<optimized out>, __pyx_args=<optimized out>, 
    __pyx_kwds=<optimized out>) at pandas/algos.c:2741
2741	in pandas/algos.c
(gdb) up
#3  0x00007ffff7994902 in _PyCFunction_FastCallDict (func_obj=0x7fffec2d53a8, args=0x1550960, 
    nargs=<optimized out>, kwargs=0x0) at Objects/methodobject.c:231
231	Objects/methodobject.c: No such file or directory.
(gdb) up
#4  0x00007ffff7a19f4c in call_function (pp_stack=0x7fffffffac58, oparg=<optimized out>, kwnames=0x0)
    at Python/ceval.c:4788
4788	Python/ceval.c: No such file or directory.

cc @jreback @martindurant

[mrocklin]

Working to narrow this down. It doesn't occur when targetting one of the parquet files rather than the entire directory. It does occur on this dask graph:

{('get-partition-0-read-parquet-f55c83a03e199bcdcf32bbc567242dcf',
  0): ('read-parquet-f55c83a03e199bcdcf32bbc567242dcf', 0),
 ('read-parquet-f55c83a03e199bcdcf32bbc567242dcf',
  0): (<function dask.dataframe.io.parquet._read_parquet_row_group>,
  <dask.bytes.core.OpenFileCreator at 0x7f8270a01160>,
  'day-0.parquet/part.0.parquet',
  None,
  ('click',
   'numeric_0',
   'numeric_1',
   'numeric_2',
   'numeric_3',
   'numeric_4',
   'numeric_5',
   'numeric_6',
   'numeric_7',
   'numeric_8',
   'numeric_9',
   'numeric_10',
   'numeric_11',
   'numeric_12',
   'category_0',
   'category_1',
   'category_2',
   'category_3',
   'category_4',
   'category_5',
   'category_6',
   'category_7',
   'category_8',
   'category_9',
   'category_10',
   'category_11',
   'category_12',
   'category_13',
   'category_14',
   'category_15',
   'category_16',
   'category_17',
   'category_18',
   'category_19',
   'category_20',
   'category_21',
   'category_22',
   'category_23',
   'category_24',
   'category_25'),
  <class 'parquet_thrift.RowGroup'>
  columns: [<class 'parquet_thrift.ColumnChunk'>
  file_offset: 2028397
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 4
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['click']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: �
      min: 
      null_count: 0
  
    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 2
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 4056866
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 2028473
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_0']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      min: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      null_count: 0
  
    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 5
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 6085342
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 4056949
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_1']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      min: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      null_count: 0
  
    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 5
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 8113818
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 6085425
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_2']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      min: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      null_count: 0
  
    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 5
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 10142294
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 8113901
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_3']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      min: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      null_count: 0
  
    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 5
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 12170770
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 10142377
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_4']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      min: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      null_count: 0
  
    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 5
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 14199246
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 12170853
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_5']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      min: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      null_count: 0
  
    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 5
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 16227722
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 14199329
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_6']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      min: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      null_count: 0
  
    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 5
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 18256198
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 16227805
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_7']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: �L
      min: b'\xff\xff\xff\xff\xff\xff\xff\xff'
      null_count: 0
  
    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 2
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 20284674
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 18256281
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_8']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: A
      min: 
      null_count: 0
  
    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 2
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 22313150
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 20284757
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_9']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      min: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      null_count: 0
  
    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 5
  
  , <class 'parquet_thrift.ColumnChunk'>
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  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
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    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_10']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      min: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
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    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
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  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 26370103
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
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    data_page_offset: 24341710
    dictionary_page_offset: None
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_11']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
      min: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
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    total_compressed_size: 2028393
    total_uncompressed_size: 2028393
    type: 5
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 28398580
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
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    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['numeric_12']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
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    total_compressed_size: 2028393
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  file_offset: 30071583
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  meta_data: <class 'parquet_thrift.ColumnMetaData'>
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    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
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  , <class 'parquet_thrift.PageEncodingStats'>
  count: 1
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  page_type: 2
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['category_0']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: None
      min: None
      null_count: 7830
  
    total_compressed_size: 1014596
    total_uncompressed_size: 1014596
    type: 6
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 30675249
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 30168116
    dictionary_page_offset: 30071658
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  , <class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 2
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['category_1']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: None
      min: None
      null_count: 0
  
    total_compressed_size: 507133
    total_uncompressed_size: 507133
    type: 6
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 31294947
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
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    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
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  count: 1
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    index_page_offset: None
    key_value_metadata: []
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    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: None
      min: None
      null_count: 0
  
    total_compressed_size: 507133
    total_uncompressed_size: 507133
    type: 6
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 31836428
  file_path: part.0.parquet
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    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
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  , <class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 2
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['category_3']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: None
      min: None
      null_count: 0
  
    total_compressed_size: 507133
    total_uncompressed_size: 507133
    type: 6
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 32427829
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
    codec: 0
    data_page_offset: 31920696
    dictionary_page_offset: 31836502
    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 0
  , <class 'parquet_thrift.PageEncodingStats'>
  count: 1
  encoding: 0
  page_type: 2
  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['category_4']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: None
      min: None
      null_count: 0
  
    total_compressed_size: 507133
    total_uncompressed_size: 507133
    type: 6
  
  , <class 'parquet_thrift.ColumnChunk'>
  file_offset: 32681548
  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
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    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
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  count: 1
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  page_type: 2
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    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['category_5']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: None
      min: None
      null_count: 0
  
    total_compressed_size: 253588
    total_uncompressed_size: 253588
    type: 6
  
  , <class 'parquet_thrift.ColumnChunk'>
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  file_path: part.0.parquet
  meta_data: <class 'parquet_thrift.ColumnMetaData'>
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    encoding_stats: [<class 'parquet_thrift.PageEncodingStats'>
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  ]
    encodings: [3, 4, 0]
    index_page_offset: None
    key_value_metadata: []
    num_values: 253545
    path_in_schema: ['category_6']
    statistics: <class 'parquet_thrift.Statistics'>
      distinct_count: None
      max: None
      min: None
      null_count: 0
  
    total_compressed_size: 507133
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    type: 6
  
  , <class 'parquet_thrift.ColumnChunk'>
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    statistics: <class 'parquet_thrift.Statistics'>
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      max: None
      min: None
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    total_compressed_size: 507133
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    type: 6
  
  , <class 'parquet_thrift.ColumnChunk'>
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  False,
  {'category_0': 1,
   'category_1': 1,
   'category_10': 1,
   'category_11': 1,
   'category_12': 1,
   'category_13': 1,
   'category_14': 1,
   'category_15': 1,
   'category_16': 1,
   'category_17': 1,
   'category_18': 1,
   'category_19': 1,
   'category_2': 1,
   'category_20': 1,
   'category_21': 1,
   'category_22': 1,
   'category_23': 1,
   'category_24': 1,
   'category_25': 1,
   'category_3': 1,
   'category_4': 1,
   'category_5': 1,
   'category_6': 1,
   'category_7': 1,
   'category_8': 1,
   'category_9': 1},
  <Parquet Schema with 41 entries>,
  {},
  {'category_0': 'category',
   'category_1': 'category',
   'category_10': 'category',
   'category_11': 'category',
   'category_12': 'category',
   'category_13': 'category',
   'category_14': 'category',
   'category_15': 'category',
   'category_16': 'category',
   'category_17': 'category',
   'category_18': 'category',
   'category_19': 'category',
   'category_2': 'category',
   'category_20': 'category',
   'category_21': 'category',
   'category_22': 'category',
   'category_23': 'category',
   'category_24': 'category',
   'category_25': 'category',
   'category_3': 'category',
   'category_4': 'category',
   'category_5': 'category',
   'category_6': 'category',
   'category_7': 'category',
   'category_8': 'category',
   'category_9': 'category',
   'click': dtype('int64'),
   'numeric_0': dtype('float64'),
   'numeric_1': dtype('float64'),
   'numeric_10': dtype('float64'),
   'numeric_11': dtype('float64'),
   'numeric_12': dtype('float64'),
   'numeric_2': dtype('float64'),
   'numeric_3': dtype('float64'),
   'numeric_4': dtype('float64'),
   'numeric_5': dtype('float64'),
   'numeric_6': dtype('float64'),
   'numeric_7': dtype('int64'),
   'numeric_8': dtype('int64'),
   'numeric_9': dtype('float64')})}

[martindurant]

To be sure: you get the error when you read the file via dask using this graph, which only loads one file, having only one row-group, but you don't get the error when you read 'day-0.parquet/part.0.parquet' directly?
I wonder how a memoryview operation in pandas could need a file.

Suspicions:

• to check the number of category labels for each column: ParquetFile.categories should list the assumed counts. The int dtype assigned to store the labels is based on these counts. Even if it was wrong, though, I think you'd only get a segfault when accessing accessing the relavant row)
• the open files logic changed recently specifically for parquet, but the code loads data into bytes, makes numpy arrays (using memoryview) and then assigns into numpy arrays within the pandas dataframe. I don't see scope for "no such file" in the context of a memoryview within pandas.

[mrocklin]

To be sure: you get the error when you read the file via dask using this graph, which only loads one file, having only one row-group, but you don't get the error when you read 'day-0.parquet/part.0.parquet' directly?

Correct

to check the number of category labels for each column: ParquetFile.categories should list the assumed counts. The int dtype assigned to store the labels is based on these counts. Even if it was wrong, though, I think you'd only get a segfault when accessing accessing the relavant row)

I'm not sure exactly what I'm looking for here, but here are is some output in case it's helpful:

In [2]: pf = fastparquet.ParquetFile('day-0.parquet/')

In [3]: pf.categories
Out[3]: 
{'category_0': 1,
 'category_1': 1,
 'category_10': 1,
 'category_11': 1,
 'category_12': 1,
 'category_13': 1,
 'category_14': 1,
 'category_15': 1,
 'category_16': 1,
 'category_17': 1,
 'category_18': 1,
 'category_19': 1,
 'category_2': 1,
 'category_20': 1,
 'category_21': 1,
 'category_22': 1,
 'category_23': 1,
 'category_24': 1,
 'category_25': 1,
 'category_3': 1,
 'category_4': 1,
 'category_5': 1,
 'category_6': 1,
 'category_7': 1,
 'category_8': 1,
 'category_9': 1}

In [4]: pf = fastparquet.ParquetFile('day-0.parquet/part.0.parquet')

In [5]: pf.categories
Out[5]: {}

In [6]: pf
Out[6]: <Parquet File: {'name': 'day-0.parquet/part.0.parquet', 'columns': ['click', 'numeric_0', 'numeric_1', 'numeric_2', 'numeric_3', 'numeric_4', 'numeric_5', 'numeric_6', 'numeric_7', 'numeric_8', 'numeric_9', 'numeric_10', 'numeric_11', 'numeric_12', 'category_0', 'category_1', 'category_2', 'category_3', 'category_4', 'category_5', 'category_6', 'category_7', 'category_8', 'category_9', 'category_10', 'category_11', 'category_12', 'category_13', 'category_14', 'category_15', 'category_16', 'category_17', 'category_18', 'category_19', 'category_20', 'category_21', 'category_22', 'category_23', 'category_24', 'category_25'], 'partitions': [], 'rows': 253545}>

[martindurant]

Are there more than one values per categorical column?
We see that the categories metadata is not being written to the component files, so this is quite possibly the problem.

[mrocklin]

There are. I'm writing dask.dataframes with categories-per-partition but for which we don't know the full set of categories.

import dask.dataframe as dd
from dask.distributed import Client
client = Client()

columns = ['click'] + ['numeric_%d' % i for i in range(13)] + ['category_%d' %  i for i in range(26)]
dtypes = {'category_%d' % i: 'category' for i in range(26)}
df = dd.read_csv('day_0', sep='\t', names=columns, header=None, dtype=dtypes)
df.to_parquet('day-0.parquet')

This is likely to be a decently common case, finding the full set of categories can be expensive. Is it possible to store categoricals efficiently without knowing the global set?

[mrocklin]

Also it looks like the individual files don't know that they should be categoricals. Though I suppose that this makes sense if we're depending on the metadata file:

In [1]: import fastparquet

In [2]: pf = fastparquet.ParquetFile('day-0.parquet/part.0.parquet')

In [3]: pf.to_pandas().dtypes
Out[3]: 
click            int64
numeric_0      float64
numeric_1      float64
numeric_2      float64
numeric_3      float64
numeric_4      float64
numeric_5      float64
numeric_6      float64
numeric_7        int64
numeric_8        int64
numeric_9      float64
numeric_10     float64
numeric_11     float64
numeric_12     float64
category_0      object
category_1      object
category_2      object
category_3      object
category_4      object
category_5      object
category_6      object
category_7      object
category_8      object
category_9      object
category_10     object
category_11     object
category_12     object
category_13     object
category_14     object
category_15     object
category_16     object
category_17     object
category_18     object
category_19     object
category_20     object
category_21     object
category_22     object
category_23     object
category_24     object
category_25     object
dtype: object

[martindurant]

This was written before dask allowed different category labels per partition...
It would be possible to store the metadata now only written at the global level for each row-group.
"don't know that they should be categoricals" - yes, this is truly a bug.

[martindurant]

Note that to test if this is indeed the cause, try passing the categories= to read_parquet as before, either as a list of column names (which assumes 2**15 labels per category) or as {col: num...} is you have a conservative guess at the number of labels.

[mrocklin]

In [1]: import dask.dataframe as dd

In [2]: df = dd.read_parquet('day-0.parquet/part.0.parquet', index=False, categories=['category_%d' % i for i in ra
   ...: nge(26)])

In [3]: df.head()
Out[3]: Segmentation fault (core dumped)

In [1]: import dask.dataframe as dd

In [2]: df = dd.read_parquet('day-0.parquet', index=False, categories=['category_%d' % i for i in range(26)])

In [3]: df.head()
Out[3]: Bus error (core dumped)

[martindurant]

Do you mind going through the columns to see if it's one particular one?

[mrocklin]

Individually they seem to be ok?

In [1]: import dask.dataframe as dd

In [2]: df = dd.read_parquet('day-0.parquet/part.0.parquet', index=False, categories=['category_%d' % i for i in range(26)])

In [3]: for i in range(26):
   ...:     print(i)
   ...:     df['category_%d' % i].head()
   ...:     
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

In [4]: df = dd.read_parquet('day-0.parquet', index=False, categories=['category_%d' % i for i in range(26)])

In [5]: for i in range(26):
   ...:     print(i)
   ...:     df['category_%d' % i].head()
   ...:     
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

[martindurant]

The number of labels in day-1 (just downloaded) is: category_8 30
category_9 43791
category_5 3
category_10 15434
category_23 6498
category_21 50357
category_6 5278
category_14 3933
category_22 13816
category_13 1474
category_1 8129
category_4 8722
category_15 51
category_18 14
category_12 9
category_17 528
category_16 3
category_11 19985
category_20 29481
category_7 1019
category_0 53586
category_25 33
category_24 47
category_2 9656
category_3 3549
category_19 55626
dtype: int64

Some of these are certainly more than 2**15. Does increasing the label count like the following avoid the error: categories={'category_%d' % i: 2**31 for i in range(26)} ?

So we can fix this to make sure the category prescription is in every row-group (this will be JSON text, so easy to decode). However, having different prescriptions per row-group would and should make the data-set unreadable by fastparquet as categorical (would require recoding each categories set to a union of cat labels).

[mrocklin]

Huzzah

In [1]: import dask.dataframe as dd

In [2]: df = dd.read_parquet('day-0.parquet', index=False, categories={'category
   ...: _%d' % i: 2**31 for i in range(26)})

In [3]: df.head()
Out[3]: 
   click  numeric_0  numeric_1  numeric_2  numeric_3  numeric_4  numeric_5  \
0      1        5.0      110.0        NaN       16.0        NaN        1.0   
1      0       32.0        3.0        5.0        NaN        1.0        0.0   
2      0        NaN      233.0        1.0      146.0        1.0        0.0   
3      0        NaN       24.0        NaN       11.0       24.0        NaN   
4      0       60.0      223.0        6.0       15.0        5.0        0.0   

   numeric_6  numeric_7  numeric_8     ...      category_16  category_17  \
0        0.0         14          7     ...         d20856aa     b8170bba   
1        0.0         61          5     ...         d20856aa     a1eb1511   
2        0.0         99          7     ...         d20856aa     628f1b8d   
3        0.0         56          3     ...         1f7fc70b     a1eb1511   
4        0.0          1          8     ...         d20856aa     d9f758ff   

   category_18  category_19 category_20 category_21 category_22 category_23  \
0     9512c20b     c38e2f28    14f65a5d    25b1b089    d7c1fc0b    7caf609c   
1     9512c20b     febfd863    a3323ca1    c8e1ee56    1752e9e8    75350c8a   
2     9512c20b     c38e2f28    14f65a5d    25b1b089    d7c1fc0b    34a9b905   
3     9512c20b          NaN         NaN         NaN    dc209cd3    b8a81fb0   
4     9512c20b     c709ec07    2b07677e    a89a92a5    aa137169    e619743b   

  category_24 category_25  
0    30436bfc    ed10571d  
1    991321ea    b757e957  
2    ff654802    ed10571d  
3    30436bfc    b757e957  
4    cdc3217e    ed10571d  

[5 rows x 40 columns]

[jcrist]

What is the status of this?

[martindurant]

Including the categories= keyword is the current workaround.
There will be no definitive solution until the pandas and arrow people have agreed with me on a prescription for metadata to put into the parquet header.