I am trying to read a table from a Google spanner database, and write it to a text file to do a backup, using google dataflow with the python sdk. I have written the following script:
from __future__ import absolute_import
import argparse
import itertools
import logging
import re
import time
import datetime as dt
import logging
import apache_beam as beam
from apache_beam.io import iobase
from apache_beam.io import WriteToText
from apache_beam.io.range_trackers import OffsetRangeTracker, UnsplittableRangeTracker
from apache_beam.metrics import Metrics
from apache_beam.options.pipeline_options import PipelineOptions
from apache_beam.options.pipeline_options import StandardOptions, SetupOptions
from apache_beam.options.pipeline_options import GoogleCloudOptions
from google.cloud.spanner.client import Client
from google.cloud.spanner.keyset import KeySet
BUCKET_URL = 'gs://my_bucket'
OUTPUT = '%s/output/' % BUCKET_URL
PROJECT_ID = 'my_project'
INSTANCE_ID = 'my_instance'
DATABASE_ID = 'my_db'
JOB_NAME = 'spanner-backup'
TABLE = 'my_table'
class SpannerSource(iobase.BoundedSource):
def __init__(self):
logging.info('Enter __init__')
self.spannerOptions = {
"id": PROJECT_ID,
"instance": INSTANCE_ID,
"database": DATABASE_ID
}
self.SpannerClient = Client
def estimate_size(self):
logging.info('Enter estimate_size')
return 1
def get_range_tracker(self, start_position=None, stop_position=None):
logging.info('Enter get_range_tracker')
if start_position is None:
start_position = 0
if stop_position is None:
stop_position = OffsetRangeTracker.OFFSET_INFINITY
range_tracker = OffsetRangeTracker(start_position, stop_position)
return UnsplittableRangeTracker(range_tracker)
def read(self, range_tracker): # This is not called when using the dataflowRunner !
logging.info('Enter read')
# instantiate spanner client
spanner_client = self.SpannerClient(self.spannerOptions["id"])
instance = spanner_client.instance(self.spannerOptions["instance"])
database = instance.database(self.spannerOptions["database"])
# read from table
table_fields = database.execute_sql("SELECT t.column_name FROM information_schema.columns AS t WHERE t.table_name = '%s'" % TABLE)
table_fields.consume_all()
self.columns = [x[0] for x in table_fields]
keyset = KeySet(all_=True)
results = database.read(table=TABLE, columns=self.columns, keyset=keyset)
# iterator over rows
results.consume_all()
for row in results:
JSON_row = {
self.columns[i]: row[i] for i in range(len(self.columns))
}
yield JSON_row
def split(self, start_position=None, stop_position=None):
# this should not be called since the source is unspittable
logging.info('Enter split')
if start_position is None:
start_position = 0
if stop_position is None:
stop_position = 1
# Because the source is unsplittable (for now), only a single source is returned
yield iobase.SourceBundle(
weight=1,
source=self,
start_position=start_position,
stop_position=stop_position)
def run(argv=None):
"""Main entry point"""
pipeline_options = PipelineOptions()
google_cloud_options = pipeline_options.view_as(GoogleCloudOptions)
google_cloud_options.project = PROJECT_ID
google_cloud_options.job_name = JOB_NAME
google_cloud_options.staging_location = '%s/staging' % BUCKET_URL
google_cloud_options.temp_location = '%s/tmp' % BUCKET_URL
#pipeline_options.view_as(StandardOptions).runner = 'DirectRunner'
pipeline_options.view_as(StandardOptions).runner = 'DataflowRunner'
p = beam.Pipeline(options=pipeline_options)
output = p | 'Get Rows from Spanner' >> beam.io.Read(SpannerSource())
iso_datetime = dt.datetime.now().replace(microsecond=0).isoformat()
output | 'Store in GCS' >> WriteToText(file_path_prefix=OUTPUT + iso_datetime + '-' + TABLE, file_name_suffix='') # if this line is commented, job completes but does not do anything
result = p.run()
result.wait_until_finish()
if __name__ == '__main__':
logging.getLogger().setLevel(logging.INFO)
run()
However, this script runs correctly only on the DirectRunner: when I let it run on the DataflowRunner, it runs for a while without any output, before exiting with an error:
"Executing failure step failure14 [...] Workflow failed. Causes: [...] The worker lost contact with the service."
Sometimes, it just goes on forever, without creating an output.
Moreover, if I comment the line 'output = ...', the job completes, but without actually reading the data.
It also appears that the dataflowRunner calls the function 'estimate_size' of the source, but not the functions 'read' or 'get_range_tracker'.
Does anyone have any ideas about what may cause this ? I know there is a (more complete) java SDK with an experimental spanner source/sink available, but if possible I'd rather stick with python.
Thanks