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# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
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# http://www.apache.org/licenses/LICENSE-2.0
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# distributed under the License is distributed on an "AS IS" BASIS,
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"""``PTransforms`` for reading from and writing to Parquet files.
Provides two read ``PTransform``\\s, ``ReadFromParquet`` and
``ReadAllFromParquet``, that produces a ``PCollection`` of records.
Each record of this ``PCollection`` will contain a single record read from
a Parquet file. Records that are of simple types will be mapped into
corresponding Python types. The actual parquet file operations are done by
pyarrow. Source splitting is supported at row group granularity.
Additionally, this module provides a write ``PTransform`` ``WriteToParquet``
that can be used to write a given ``PCollection`` of Python objects to a
Parquet file.
"""
from __future__ import absolute_import
from functools import partial
from apache_beam.io import filebasedsink
from apache_beam.io import filebasedsource
from apache_beam.io.filesystem import CompressionTypes
from apache_beam.io.iobase import RangeTracker
from apache_beam.io.iobase import Read
from apache_beam.io.iobase import Write
from apache_beam.transforms import DoFn
from apache_beam.transforms import ParDo
from apache_beam.transforms import PTransform
try:
import pyarrow as pa
import pyarrow.parquet as pq
except ImportError:
pa = None
pq = None
__all__ = ['ReadFromParquet', 'ReadAllFromParquet', 'ReadFromParquetBatched',
'ReadAllFromParquetBatched', 'WriteToParquet']
class _ArrowTableToRowDictionaries(DoFn):
""" A DoFn that consumes an Arrow table and yields a python dictionary for
each row in the table."""
def process(self, table):
num_rows = table.num_rows
data_items = table.to_pydict().items()
for n in range(num_rows):
row = {}
for column, values in data_items:
row[column] = values[n]
yield row
[docs]class ReadFromParquetBatched(PTransform):
"""A :class:`~apache_beam.transforms.ptransform.PTransform` for reading
Parquet files as a `PCollection` of `pyarrow.Table`. This `PTransform` is
currently experimental. No backward-compatibility guarantees."""
def __init__(self, file_pattern=None, min_bundle_size=0,
validate=True, columns=None):
""" Initializes :class:`~ReadFromParquetBatched`
An alternative to :class:`~ReadFromParquet` that yields each row group from
the Parquet file as a `pyarrow.Table`. These Table instances can be
processed directly, or converted to a pandas DataFrame for processing. For
more information on supported types and schema, please see the pyarrow
documentation.
.. testcode::
with beam.Pipeline() as p:
dataframes = p \\
| 'Read' >> beam.io.ReadFromParquetBatched('/mypath/mypqfiles*') \\
| 'Convert to pandas' >> beam.Map(lambda table: table.to_pandas())
.. NOTE: We're not actually interested in this error; but if we get here,
it means that the way of calling this transform hasn't changed.
.. testoutput::
:hide:
Traceback (most recent call last):
...
IOError: No files found based on the file pattern
See also: :class:`~ReadFromParquet`.
Args:
file_pattern (str): the file glob to read
min_bundle_size (int): the minimum size in bytes, to be considered when
splitting the input into bundles.
validate (bool): flag to verify that the files exist during the pipeline
creation time.
columns (List[str]): list of columns that will be read from files.
A column name may be a prefix of a nested field, e.g. 'a' will select
'a.b', 'a.c', and 'a.d.e'
"""
super(ReadFromParquetBatched, self).__init__()
self._source = _create_parquet_source(
file_pattern,
min_bundle_size,
validate=validate,
columns=columns,
)
[docs] def expand(self, pvalue):
return pvalue.pipeline | Read(self._source)
[docs] def display_data(self):
return {'source_dd': self._source}
[docs]class ReadFromParquet(PTransform):
"""A :class:`~apache_beam.transforms.ptransform.PTransform` for reading
Parquet files as a `PCollection` of dictionaries. This `PTransform` is
currently experimental. No backward-compatibility guarantees."""
def __init__(self, file_pattern=None, min_bundle_size=0,
validate=True, columns=None):
"""Initializes :class:`ReadFromParquet`.
Uses source ``_ParquetSource`` to read a set of Parquet files defined by
a given file pattern.
If ``/mypath/myparquetfiles*`` is a file-pattern that points to a set of
Parquet files, a :class:`~apache_beam.pvalue.PCollection` for the records in
these Parquet files can be created in the following manner.
.. testcode::
with beam.Pipeline() as p:
records = p | 'Read' >> beam.io.ReadFromParquet('/mypath/mypqfiles*')
.. NOTE: We're not actually interested in this error; but if we get here,
it means that the way of calling this transform hasn't changed.
.. testoutput::
:hide:
Traceback (most recent call last):
...
IOError: No files found based on the file pattern
Each element of this :class:`~apache_beam.pvalue.PCollection` will contain
a Python dictionary representing a single record. The keys will be of type
:class:`str` and named after their corresponding column names. The values
will be of the type defined in the corresponding Parquet schema. Records
that are of simple types will be mapped into corresponding Python types.
Records that are of complex types like list and struct will be mapped to
Python list and dictionary respectively. For more information on supported
types and schema, please see the pyarrow documentation.
See also: :class:`~ReadFromParquetBatched`.
Args:
file_pattern (str): the file glob to read
min_bundle_size (int): the minimum size in bytes, to be considered when
splitting the input into bundles.
validate (bool): flag to verify that the files exist during the pipeline
creation time.
columns (List[str]): list of columns that will be read from files.
A column name may be a prefix of a nested field, e.g. 'a' will select
'a.b', 'a.c', and 'a.d.e'
"""
super(ReadFromParquet, self).__init__()
self._source = _create_parquet_source(
file_pattern,
min_bundle_size,
validate=validate,
columns=columns,
)
[docs] def expand(self, pvalue):
return pvalue | Read(self._source) | ParDo(_ArrowTableToRowDictionaries())
[docs] def display_data(self):
return {'source_dd': self._source}
[docs]class ReadAllFromParquetBatched(PTransform):
"""A ``PTransform`` for reading ``PCollection`` of Parquet files.
Uses source ``_ParquetSource`` to read a ``PCollection`` of Parquet files or
file patterns and produce a ``PCollection`` of ``pyarrow.Table``, one for
each Parquet file row group. This ``PTransform`` is currently experimental.
No backward-compatibility guarantees.
"""
DEFAULT_DESIRED_BUNDLE_SIZE = 64 * 1024 * 1024 # 64MB
def __init__(self, min_bundle_size=0,
desired_bundle_size=DEFAULT_DESIRED_BUNDLE_SIZE,
columns=None,
label='ReadAllFiles'):
"""Initializes ``ReadAllFromParquet``.
Args:
min_bundle_size: the minimum size in bytes, to be considered when
splitting the input into bundles.
desired_bundle_size: the desired size in bytes, to be considered when
splitting the input into bundles.
columns: list of columns that will be read from files. A column name
may be a prefix of a nested field, e.g. 'a' will select
'a.b', 'a.c', and 'a.d.e'
"""
super(ReadAllFromParquetBatched, self).__init__()
source_from_file = partial(
_create_parquet_source,
min_bundle_size=min_bundle_size,
columns=columns
)
self._read_all_files = filebasedsource.ReadAllFiles(
True, CompressionTypes.UNCOMPRESSED, desired_bundle_size,
min_bundle_size, source_from_file)
self.label = label
[docs] def expand(self, pvalue):
return pvalue | self.label >> self._read_all_files
[docs]class ReadAllFromParquet(PTransform):
def __init__(self, **kwargs):
self._read_batches = ReadAllFromParquetBatched(**kwargs)
[docs] def expand(self, pvalue):
return pvalue | self._read_batches | ParDo(_ArrowTableToRowDictionaries())
def _create_parquet_source(file_pattern=None,
min_bundle_size=0,
validate=False,
columns=None):
return \
_ParquetSource(
file_pattern=file_pattern,
min_bundle_size=min_bundle_size,
validate=validate,
columns=columns,
)
class _ParquetUtils(object):
@staticmethod
def find_first_row_group_index(pf, start_offset):
for i in range(_ParquetUtils.get_number_of_row_groups(pf)):
row_group_start_offset = _ParquetUtils.get_offset(pf, i)
if row_group_start_offset >= start_offset:
return i
return -1
@staticmethod
def get_offset(pf, row_group_index):
first_column_metadata =\
pf.metadata.row_group(row_group_index).column(0)
if first_column_metadata.has_dictionary_page:
return first_column_metadata.dictionary_page_offset
else:
return first_column_metadata.data_page_offset
@staticmethod
def get_number_of_row_groups(pf):
return pf.metadata.num_row_groups
class _ParquetSource(filebasedsource.FileBasedSource):
"""A source for reading Parquet files.
"""
def __init__(self, file_pattern, min_bundle_size, validate, columns):
super(_ParquetSource, self).__init__(
file_pattern=file_pattern,
min_bundle_size=min_bundle_size,
validate=validate
)
self._columns = columns
def read_records(self, file_name, range_tracker):
next_block_start = -1
def split_points_unclaimed(stop_position):
if next_block_start >= stop_position:
# Next block starts at or after the suggested stop position. Hence
# there will not be split points to be claimed for the range ending at
# suggested stop position.
return 0
return RangeTracker.SPLIT_POINTS_UNKNOWN
range_tracker.set_split_points_unclaimed_callback(split_points_unclaimed)
start_offset = range_tracker.start_position()
if start_offset is None:
start_offset = 0
with self.open_file(file_name) as f:
pf = pq.ParquetFile(f)
# find the first dictionary page (or data page if there's no dictionary
# page available) offset after the given start_offset. This offset is also
# the starting offset of any row group since the Parquet specification
# describes that the data pages always come first before the meta data in
# each row group.
index = _ParquetUtils.find_first_row_group_index(pf, start_offset)
if index != -1:
next_block_start = _ParquetUtils.get_offset(pf, index)
else:
next_block_start = range_tracker.stop_position()
number_of_row_groups = _ParquetUtils.get_number_of_row_groups(pf)
while range_tracker.try_claim(next_block_start):
table = pf.read_row_group(index, self._columns)
if index + 1 < number_of_row_groups:
index = index + 1
next_block_start = _ParquetUtils.get_offset(pf, index)
else:
next_block_start = range_tracker.stop_position()
yield table
[docs]class WriteToParquet(PTransform):
"""A ``PTransform`` for writing parquet files.
This ``PTransform`` is currently experimental. No backward-compatibility
guarantees.
"""
def __init__(self,
file_path_prefix,
schema,
row_group_buffer_size=64*1024*1024,
record_batch_size=1000,
codec='none',
use_deprecated_int96_timestamps=False,
file_name_suffix='',
num_shards=0,
shard_name_template=None,
mime_type='application/x-parquet'):
"""Initialize a WriteToParquet transform.
Writes parquet files from a :class:`~apache_beam.pvalue.PCollection` of
records. Each record is a dictionary with keys of a string type that
represent column names. Schema must be specified like the example below.
.. testsetup::
from tempfile import NamedTemporaryFile
import glob
import os
import pyarrow
filename = NamedTemporaryFile(delete=False).name
.. testcode::
with beam.Pipeline() as p:
records = p | 'Read' >> beam.Create(
[{'name': 'foo', 'age': 10}, {'name': 'bar', 'age': 20}]
)
_ = records | 'Write' >> beam.io.WriteToParquet(filename,
pyarrow.schema(
[('name', pyarrow.binary()), ('age', pyarrow.int64())]
)
)
.. testcleanup::
for output in glob.glob('{}*'.format(filename)):
os.remove(output)
For more information on supported types and schema, please see the pyarrow
document.
Args:
file_path_prefix: The file path to write to. The files written will begin
with this prefix, followed by a shard identifier (see num_shards), and
end in a common extension, if given by file_name_suffix. In most cases,
only this argument is specified and num_shards, shard_name_template, and
file_name_suffix use default values.
schema: The schema to use, as type of ``pyarrow.Schema``.
row_group_buffer_size: The byte size of the row group buffer. Note that
this size is for uncompressed data on the memory and normally much
bigger than the actual row group size written to a file.
record_batch_size: The number of records in each record batch. Record
batch is a basic unit used for storing data in the row group buffer.
A higher record batch size implies low granularity on a row group buffer
size. For configuring a row group size based on the number of records,
set ``row_group_buffer_size`` to 1 and use ``record_batch_size`` to
adjust the value.
codec: The codec to use for block-level compression. Any string supported
by the pyarrow specification is accepted.
use_deprecated_int96_timestamps: Write nanosecond resolution timestamps to
INT96 Parquet format. Defaults to False.
file_name_suffix: Suffix for the files written.
num_shards: The number of files (shards) used for output. If not set, the
service will decide on the optimal number of shards.
Constraining the number of shards is likely to reduce
the performance of a pipeline. Setting this value is not recommended
unless you require a specific number of output files.
shard_name_template: A template string containing placeholders for
the shard number and shard count. When constructing a filename for a
particular shard number, the upper-case letters 'S' and 'N' are
replaced with the 0-padded shard number and shard count respectively.
This argument can be '' in which case it behaves as if num_shards was
set to 1 and only one file will be generated. The default pattern used
is '-SSSSS-of-NNNNN' if None is passed as the shard_name_template.
mime_type: The MIME type to use for the produced files, if the filesystem
supports specifying MIME types.
Returns:
A WriteToParquet transform usable for writing.
"""
super(WriteToParquet, self).__init__()
self._sink = \
_create_parquet_sink(
file_path_prefix,
schema,
codec,
row_group_buffer_size,
record_batch_size,
use_deprecated_int96_timestamps,
file_name_suffix,
num_shards,
shard_name_template,
mime_type
)
[docs] def expand(self, pcoll):
return pcoll | Write(self._sink)
[docs] def display_data(self):
return {'sink_dd': self._sink}
def _create_parquet_sink(file_path_prefix,
schema,
codec,
row_group_buffer_size,
record_batch_size,
use_deprecated_int96_timestamps,
file_name_suffix,
num_shards,
shard_name_template,
mime_type):
return \
_ParquetSink(
file_path_prefix,
schema,
codec,
row_group_buffer_size,
record_batch_size,
use_deprecated_int96_timestamps,
file_name_suffix,
num_shards,
shard_name_template,
mime_type
)
class _ParquetSink(filebasedsink.FileBasedSink):
"""A sink for parquet files."""
def __init__(self,
file_path_prefix,
schema,
codec,
row_group_buffer_size,
record_batch_size,
use_deprecated_int96_timestamps,
file_name_suffix,
num_shards,
shard_name_template,
mime_type):
super(_ParquetSink, self).__init__(
file_path_prefix,
file_name_suffix=file_name_suffix,
num_shards=num_shards,
shard_name_template=shard_name_template,
coder=None,
mime_type=mime_type,
# Compression happens at the block level using the supplied codec, and
# not at the file level.
compression_type=CompressionTypes.UNCOMPRESSED)
self._schema = schema
self._codec = codec
self._row_group_buffer_size = row_group_buffer_size
self._use_deprecated_int96_timestamps = use_deprecated_int96_timestamps
self._buffer = [[] for _ in range(len(schema.names))]
self._buffer_size = record_batch_size
self._record_batches = []
self._record_batches_byte_size = 0
self._file_handle = None
def open(self, temp_path):
self._file_handle = super(_ParquetSink, self).open(temp_path)
return pq.ParquetWriter(
self._file_handle, self._schema, compression=self._codec,
use_deprecated_int96_timestamps=self._use_deprecated_int96_timestamps
)
def write_record(self, writer, value):
if len(self._buffer[0]) >= self._buffer_size:
self._flush_buffer()
if self._record_batches_byte_size >= self._row_group_buffer_size:
self._write_batches(writer)
# reorder the data in columnar format.
for i, n in enumerate(self._schema.names):
self._buffer[i].append(value[n])
def close(self, writer):
if len(self._buffer[0]) > 0:
self._flush_buffer()
if self._record_batches_byte_size > 0:
self._write_batches(writer)
writer.close()
if self._file_handle:
self._file_handle.close()
self._file_handle = None
def display_data(self):
res = super(_ParquetSink, self).display_data()
res['codec'] = str(self._codec)
res['schema'] = str(self._schema)
res['row_group_buffer_size'] = str(self._row_group_buffer_size)
return res
def _write_batches(self, writer):
table = pa.Table.from_batches(self._record_batches)
self._record_batches = []
self._record_batches_byte_size = 0
writer.write_table(table)
def _flush_buffer(self):
arrays = [[] for _ in range(len(self._schema.names))]
for x, y in enumerate(self._buffer):
arrays[x] = pa.array(y, type=self._schema.types[x])
self._buffer[x] = []
rb = pa.RecordBatch.from_arrays(arrays, self._schema.names)
self._record_batches.append(rb)
size = 0
for x in arrays:
for b in x.buffers():
size = size + b.size
self._record_batches_byte_size = self._record_batches_byte_size + size