Exception: ValueError('buffer source array is read-only')

[astrojuanlu]

(Comes from #1978 (comment))

What happened:

$ ipython
Python 3.8.3 (default, May 20 2020, 12:50:54) 
Type 'copyright', 'credits' or 'license' for more information
IPython 7.15.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: # coding: utf-8 
   ...: from dask import dataframe as dd 
   ...: import pandas as pd 
   ...: from distributed import Client 
   ...: client = Client() 
   ...: df = dd.read_csv("../data/yellow_tripdata_2019-*.csv", parse_dates=["tpep_pickup_datetime", "tpep_dropoff_datetime"]) 
   ...: payment_types = { 
   ...:     1: "Credit Card", 
   ...:     2: "Cash", 
   ...:     3: "No Charge", 
   ...:     4: "Dispute", 
   ...:     5: "Unknown", 
   ...:     6: "Voided trip" 
   ...: } 
   ...: payment_names = pd.Series( 
   ...:     payment_types, name="payment_name" 
   ...: ).to_frame() 
   ...: df2 = df.merge( 
   ...:     payment_names, left_on="payment_type", right_index=True 
   ...: ) 
   ...: op = df2.groupby("payment_name")["tip_amount"].mean() 
   ...: client.compute(op) 
   ...:                                                                                                                                                                                                                                       
Out[1]: <Future: pending, key: finalize-85edcc1f23785545f628c932abd19768>

In [2]: distributed.worker - WARNING -  Compute Failed                                                                                                                                                                                        
Function:  _apply_chunk
args:      (        VendorID tpep_pickup_datetime tpep_dropoff_datetime  passenger_count  trip_distance  RatecodeID store_and_fwd_flag  ...  mta_tax  tip_amount  tolls_amount  improvement_surcharge  total_amount  congestion_surcharge  payment_name
0              1  2019-01-04 14:08:46   2019-01-04 14:18:10                1           1.70           1                  N  ...      0.5         0.0          0.00                    0.3          9.30                   NaN          Cash
1              1  2019-01-04 14:20:33   2019-01-04 14:25:10                1           0.90           1                  N  ...      0.5         0.0          0.00                    0.3          6.30                   NaN          Cash
13             2  2019-01-04 14:14:45   2019-01-04 14:26:00                5           1.63           1                  N  ...      0.5         0.0          0.00                    0.3          9.80                   NaN          Cash
15             2  2019-01-04 14:49:45   2019-01-04 15:0
kwargs:    {'chunk': <methodcaller: sum>, 'columns': 'tip_amount'}
Exception: ValueError('buffer source array is read-only')

In [2]:                                                                                                                                                                                                                                       

In [2]: client                                                                                                                                                                                                                                
Out[2]: <Client: 'tcp://127.0.0.1:33689' processes=4 threads=4, memory=16.70 GB>

In [3]: _1                                                                                                                                                                                                                                    
Out[3]: <Future: error, key: finalize-85edcc1f23785545f628c932abd19768>

What you expected to happen: The operation finishes without error.

Minimal Complete Verifiable Example:

# coding: utf-8
from dask import dataframe as dd
import pandas as pd
from distributed import Client
client = Client()
df = dd.read_csv("../data/yellow_tripdata_2019-*.csv", parse_dates=["tpep_pickup_datetime", "tpep_dropoff_datetime"])
payment_types = {
    1: "Credit Card",
    2: "Cash",
    3: "No Charge",
    4: "Dispute",
    5: "Unknown",
    6: "Voided trip"
}
payment_names = pd.Series(
    payment_types, name="payment_name"
).to_frame()
df2 = df.merge(
    payment_names, left_on="payment_type", right_index=True
)
op = df2.groupby("payment_name")["tip_amount"].mean()
client.compute(op)

Data:

https://s3.amazonaws.com/nyc-tlc/trip+data/yellow_tripdata_2019-01.csv
https://s3.amazonaws.com/nyc-tlc/trip+data/yellow_tripdata_2019-02.csv
https://s3.amazonaws.com/nyc-tlc/trip+data/yellow_tripdata_2019-03.csv
https://s3.amazonaws.com/nyc-tlc/trip+data/yellow_tripdata_2019-04.csv

Anything else we need to know?: I managed to avoid this error by reducing the number of files, but then it hit me again at a later point. I expect this behavior to be dependent on the available RAM.

Environment:

• Dask version: 2.18.1
• Python version: 3.8.3
• Operating System: Linux Mint 19.3
• Install method (conda, pip, source): pip

[jakirkham]

Is it possible to reproduce this without the Taxi data? Would some randomly generated data work as well?

[astrojuanlu]

Perhaps, although it will take me more time to narrow down the example. I managed to reproduce the problem with these URLs (stripped out some files with mixed dtypes) and without the intermediate merge:

yellow_tripdata_2019-01.csv
yellow_tripdata_2019-02.csv
yellow_tripdata_2019-03.csv
yellow_tripdata_2019-04.csv
yellow_tripdata_2019-05.csv
yellow_tripdata_2019-06.csv
yellow_tripdata_2019-12.csv

# coding: utf-8
from dask import dataframe as dd
from distributed import Client

client = Client()

df = dd.read_csv("../data/yellow_tripdata_2019-*.csv", parse_dates=["tpep_pickup_datetime", "tpep_dropoff_datetime"])

op = df.groupby("payment_type")["tip_amount"].mean()
client.compute(op)

However, removing one file resulted in the operation executing successfully. I'll try to see if this can be simplified further.

[jakirkham]

Thanks Juan! 😀

[quasiben]

When I ran this I got the mismatched dtype error:

In [7]: /Users/bzaitlen/Documents/GitHub/distributed/distributed/worker.py:3312: DtypeWarning: Columns (6) have mixed types.Specify dtype option on import or set low_memory=False.
  return func(*map(execute_task, args))
distributed.worker - WARNING -  Compute Failed
Function:  execute_task
args:      ((<function check_meta at 0x1132a88c0>, (<function apply at 0x100dd8b00>, <function pandas_read_text at 0x113380dd0>, [<function _make_parser_function.<locals>.parser_f at 0x114baf710>, (<function read_block_from_file at 0x114b2c830>, <OpenFile '/Users/bzaitlen/Downloads/yellow_tripdata_2019-12.csv'>, 576000000, 64000000, b'\n'), b'VendorID,tpep_pickup_datetime,tpep_dropoff_datetime,passenger_count,trip_distance,RatecodeID,store_and_fwd_flag,PULocationID,DOLocationID,payment_type,fare_amount,extra,mta_tax,tip_amount,tolls_amount,improvement_surcharge,total_amount,congestion_surcharge\r\n', (<class 'dict'>, [['parse_dates', ['tpep_pickup_datetime', 'tpep_dropoff_datetime']]]), (<class 'dict'>, [['VendorID', dtype('int64')], ['tpep_pickup_datetime', dtype('<M8[ns]')], ['tpep_dropoff_datetime', dtype('<M8[ns]')], ['passenger_count', dtype('int64')], ['trip_distance', dtype('float64')], ['RatecodeID', dtype('int64')], ['store_and_fwd_flag', dtype('O')], ['PULocationID', dtype('int64')], ['
kwargs:    {}
Exception: ValueError("Mismatched dtypes found in `pd.read_csv`/`pd.read_table`.\n\n+-----------------+---------+----------+\n| Column          | Found   | Expected |\n+-----------------+---------+----------+\n| RatecodeID      | float64 | int64    |\n| VendorID        | float64 | int64    |\n| passenger_count | float64 | int64    |\n| payment_type    | float64 | int64    |\n+-----------------+---------+----------+\n\nUsually this is due to dask's dtype inference failing, and\n*may* be fixed by specifying dtypes manually by adding:\n\ndtype={'RatecodeID': 'float64',\n       'VendorID': 'float64',\n       'passenger_count': 'float64',\n       'payment_type': 'float64'}\n\nto the call to `read_csv`/`read_table`.\n\nAlternatively, provide `assume_missing=True` to interpret\nall unspecified integer columns as floats.")

[jakirkham]

FWIW I tried to ensure that we always create bytearrays in merge_frames (part of the serialization/deserialization pipeline) with PR ( #3918 ). That would ensure all the buffers backing data is writeable. It seems to work on a trivial NumPy test include in that PR. Maybe that helps? Would you be able to try it @astrojuanlu?

[astrojuanlu]

I confirm that #3918 fixed the issue with the same data:

In [1]: from dask import dataframe as dd 
   ...: from distributed import Client 
   ...:  
   ...: client = Client() 
   ...:  
   ...: df = dd.read_csv("../data/yellow_tripdata_2019-*.csv", parse_dates=["tpep_pickup_datetime", "tpep_dropoff_datetime"]) 
   ...:  
   ...: op = df.groupby("payment_type")["tip_amount"].mean() 
   ...: client.compute(op)                                                                                                                                                                                                                    
Out[1]: <Future: pending, key: finalize-d2d79ddf9a418b1c0ed76bfa1c20daf6>

In [2]: _1                                                                                                                                                                                                                                    
Out[2]: <Future: finished, type: pandas.Series, key: finalize-d2d79ddf9a418b1c0ed76bfa1c20daf6>

In [3]: _1.result()                                                                                                                                                                                                                           
Out[3]: 
payment_type
1    2.976392
2    0.000326
3    0.625695
4   -0.010395
5    0.000000
Name: tip_amount, dtype: float64

[jakirkham]

Thanks Juan! 😀

Will look at cleaning it up and adding some more tests.

[jakirkham]

Adding a test for a Pandas Series as well in PR ( #3995 ).